Dissertations / Theses on the topic 'Orthokeratology'

This research aimed to develop and validate a new method for calculating anterior and posterior corneal topography. The novel calculation method was then used to evaluate the influence of orthokeratology (OK) lens wear and overnight edema on posterior corneal shape, and to develop a physical model for anterior and posterior corneal shape changes during myopic overnight OK. The new method uses anterior corneal topographic data derived from the Medmont E300 corneal topographer, and total corneal thickness data measured along the horizontal corneal meridian using the Holden-Payor optical pachometer. The data are then entered into an Interactive Data Language computer program, which calculates the anterior and posterior corneal apical radii of curvature and Q (asphericity) based on the calculated anterior ellipsoid curve, the locations of corneal pachometry measurements, direction of thickness measurements, and the local radius of curvature. Pachometry data were optimised based on the local radius of anterior corneal curvature and an exact solution for the relationship between real and apparent thickness. The newly developed method was validated using a range of test surfaces and repeatability was also investigated with five adult subjects. Eighteen young adult subjects wore BE OK lenses overnight only in both eyes for 14 days. Ten young adult subjects participated as a control group, wearing J-Contour RGP lenses in one eye only for one night. OK subjects were assessed on days 1, 4, 7, and 14, and control group subjects on day 1, in the morning and evening. Subjective refraction, visual acuity, corneal topography and corneal thickness were measured. Most change in refractive error occurred within the first 7 nights of overnight OK. This rapid reduction in myopia was associated with improvement in unaided VA, and flattening of anterior corneal curvature. There were no changes in posterior corneal apical radius but an increase towards an oblate posterior corneal Q was found during 14 days of overnight OK, at both morning and evening measurements. Fixed anterior corneal points were determined at 8.13mm and 5.30mm chords at morning and evening measurements in the OK group. The points of maximum increase in anterior corneal elevation at evening and morning measurements were at 6.90mm and 7.00mm chords respectively. In the OK group, significant backwards movement of anterior and posterior corneal apices was found relative to the fixed anterior corneal points at the morning measurement. Backwards movement of the anterior corneal apex remained during the day whereas the posterior corneal apex recovered to baseline. In conclusion, our results support the theory that the OK refractive effect is achieved through remodelling of anterior corneal layers, without overall corneal bending. Central corneal thinning in the evening after overnight OK lens wear is primarily due to to posterior movement in space of the anterior corneal apex. The posterior direction of overnight corneal edema across the cornea in OK lens wear is consistent with previous models that predict that the cornea swells in a posterior direction during edema.

Orthokeratology (OK) is the reduction, modification or elimination of myopia through application of contact lenses. With the development of high Dk/t lens materials, overnight therapy has become the modality of choice for OK. Overnight OK lens wear has been previously investigated in terms of its efficacy to reduce myopia. However, the underlying effects of overnight OK lens wear on the human cornea have received less attention. As well as the clinical efficacy of overnight OK, this study investigated the effects of overnight OK on topographical corneal thickness and the overnight corneal edema response, and corneal tissue changes with overnight OK. Eighteen subjects participated as the OK lens-wearing group, wearing BE lenses (UltraVision, Brisbane, Queensland) in both eyes. A further ten subjects participated as control subjects, wearing conventional rigid lenses (J-Contour, UltraVision) in the right eye (RE) only. The left eye (LE) acted as a non-lens-wearing control. Both groups wore lenses overnight only, with no lens wear during the day. Measurements were conducted at baseline then on day 1, 4, 10, 30, 60, and 90 for the OK lens-wearing eyes; and up to day 30 for the control group, in the morning (after overnight lens wear) and in the evening (after 8-10 hours of lens removal). Variables measured included best vision sphere (BVS), unaided logMAR visual acuity (VA), refractive astigmatism, apical corneal power (ACP), simulated K readings (Medmont E300 corneal topographer), topographical corneal thickness (Holden-Payor optical pachometer), and keratocyte and endothelial cell densities (ConfoScan2 confocal microscope). Approximately 75% of myopia was corrected after the first night of OK lens wear and the changes in refractive error stabilised by day 10. By day 90, myopia reduction averaged 2.54 ?? 0.63 D. This was associated with significant improvement in unaided VA of about 82% after the first night of lens wear. There was no change in refractive astigmatism over the 3-month period. There was significant reduction in ACP in the OK lens-wearing eyes after the first night of lens wear, which accounted for more than 70% of the total ACP change over the 3-month period (RE: -2.16 ?? 0.53 D; LE: -2.11 ?? 0.86 D). There was significant central epithelial thinning (about 30%) and significant thickening (about 3%) in the mid-peripheral stroma in the OK lens-wearing eyes. Significant central epithelial thinning was found after the first night of lens wear while thickening in the mid-peripheral stroma reached statistical significance by day 4. Further analysis suggests that topographical corneal thickness changes account for the refractive error changes with overnight OK lens wear, rather than corneal bending. The central overnight stromal edema response was significantly reduced in the OK lens-wearing eyes (1.2 ?? 0.5%) to a level lower than in the conventional RGP (6.2 ?? 1.2%) and non-lens-wearing eyes (2.5 ?? 0.9%) in the control group. Mid-peripheral and peripheral stromal edema responses showed similar levels to those predicted based on lens Dk/t. A single overnight wear of BE and Paragon Corneal Refractive Therapy (CRT) lenses showed that the edema response to BE lens wear is significantly less than in the CRT lens-wearing eyes (BE: 2.5 ?? 0.7%; CRT 3.5 ?? 1.3%) immediately on eye opening. No significant changes were found in either central stromal keratocyte or endothelial cell densities in either OK or control groups over the study period. In conclusion, overnight OK lens wear induces significant reductions in myopia after the first night of lens wear associated with improvement in unaided VA. Overnight OK lens wear causes significant thinning in the central epithelium and significant mid-peripheral stromal thickening which results in flattening of the central cornea and steepening in the mid-periphery. Although there were no significant changes in central stromal keratocyte and endothelial cell densities, thinning of the central epithelial layer raises concerns regarding the safety of the procedure, especially with the alarming number of corneal infections reported recently in the literature.

This work investigates two key questions: ; how myopia progression control treatments impact accommodation and binocular vision function and if accommodation and binocular vision function prior to myopia control interventions has any association with the efficacy of treatment. The work is made up of four main studies. Study 1 was a review and re-analysis of a previously completed study to investigate whether there are any possible associations between accommodation and binocular vision status prior to lens wear which may impact the myopia control efficacy of orthokeratology lens treatment. The data of 26 children were used. The study involved using an orthokeratology lens in one eye, with the contralateral eye used as a rigid gas permeable lens wearing control. Given the unusual nature of this modality, accommodation and binocular vision status was measured at baseline and monitored throughout the study to ensure that there were no adverse responses to lens wear. In a novel analysis of pre-existing data, the accommodation and binocular vision profiles of those participants that responded the best to orthokeratology lens treatment in terms of inhibiting ocular axial length growth were compared to those that did not respond to treatment. A similar comparison was made between those participants who progressed the most to the least in the control eye. Results from this analysis suggested that accommodation and binocular vision status prior to orthokeratology lens wear may be associated with treatment effect. Orthokeratology lens treatment worked best for myopia control when accommodative facility was higher and closer to population norms, AC/A ratio was lower and closer to population norms and accommodative lag was higher. None of these associations reached statistical significance, however further investigation appeared warranted. Interestingly, baseline near phoria did not appear to have an influence on response to treatment with orthokeratology lens wear. This is different to bifocal spectacle lens wear studies that show that initial near phoria has an impact on the efficacy of myopia control treatment. Study 2 was a review of clinical records of 37 children and young adult patients seen in two private optometric practices in Australia. Accommodation and binocular vision function prior to orthokeratology lens wear was compared to during lens wear in patients who were fitted with orthokeratology lenses between 2010 and 2012. The results of this study showed that there was a statistically significant change in mean near phoria in the exo direction with lens wear. Mean positive relative accommodation increased, mean negative relative accommodation decreased and accommodative facility increased. While the mean distance phoria remained unchanged there was a statistically significant reduction in the standard deviation of this variable. There was a slight reduction in mean lag of accommodation, but it failed to reach statistical significance. The study showed that the binocular vision status including accommodative and vergence measures changed during orthokeratology lens wear. The changes were in a direction closer to population norms. Study 3 was a prospective study of the impact of short-term orthokeratology lens wear on binocular vision in 12 young adults. Measurements of binocular vision status were taken at baseline and after one month of lens wear. The results of this study were similar to Study 2. There was no statistically significant change in mean near phoria. Distance accommodative facility increased. There was a slight, but not statistically significant, change in mean near accommodative facility Again, while there was no change in mean distance phoria, there was a significant reduction in the standard deviation of this variable. Additional variables of interest in this study included stereopsis, which was unchanged, and fixation disparity at distance and near which were unchanged. This short-term study showed that orthokeratology lens wear alters binocular vision status including accommodative and vergence measures. Again, the changes in binocular vision were in a direction closer to population norms. Study 4 was a record review of patients seen in the Myopia Control Clinic at the University of New South Wales, Sydney, Australia. The accommodation and binocular vision function of myopic children treated with orthokeratology lens wear or low dose atropine were reviewed. A total of 9 children treated with orthokeratology were followed for 3 to 6 months. Mean near phoria moved in the exo direction with orthokeratology lens wear and gradient AC/A ratio moved to more normal values with lens wear. There was an association between annualised axial length growth and gradient AC/A ratios and stereopsis, suggesting that baseline accommodation and binocular vision function may influence treatment. A total of 19 children were treated with low dose atropine and data were available from 3 to 6 months of treatment. Low dose atropine led to a small but not statistically significant decrease in amplitude of accommodation. Patients who were the worst responders to low dose atropine had lower baseline amplitude of accommodation compared to the best responders. Although speculative, the reduction in amplitude of accommodation may have a detrimental impact on the accommodation and binocular vision function and increase blur. Alternatively, those patients with high amplitude of accommodation may benefit from a subtle change in the accommodation and vergence relationship Both accommodation and vergence measures of binocular vision status appear to change with orthokeratology lens wear. The changes in binocular vision move in a direction closer to population norms; this is a novel finding of this thesis and is not reported elsewhere. Binocular vision that is abnormal has been associated with onset of myopia and progression. The changes in binocular vision associated with orthokeratology lens wear may contribute to the myopia progression control effect. Close monitoring of accommodation and binocular vision during myopia progression treatment is warranted.

Orthokeratology (OK) is a specialty contact lens procedure that involves the overnight wear of lenses to reshape the corneal tissue resulting in clear vision upon lens removal. Currently it is the only way of achieving clear vision without having to wear spectacles or contact lenses during the day or undergoing refractive surgery. This thesis investigated the effects of this procedure on the corneal epithelium and the potential increase in risk of microbial infection in an animal model. The cat was first established as an appropriate animal model in a pilot study to examine OK epithelial changes. Initial findings of epithelial thickness changes similar to those found with human myopic and hyperopic OK clinical studies led to the further development of this animal model to better mimic human lens wear for the remaining studies undertaken. Histological studies were used to examine epithelial effects of overnight myopic OK lens wear. Repeatable and differential effects on epithelial thickness and morphology across the cornea were found, including thinning of the central and peripheral epithelium and thickening of the mid-peripheral epithelium. Central thinning was attributed to compression of cells and was less in overnight wear compared to continuous wear. Mid-peripheral thickening was due to increased cell layers and peripheral thinning was attributed to cellular compression. Recovery of epithelial morphologic and thickness changes commenced one day after ceasing lens wear and was complete within one week. Minimal changes to keratocyte populations in regions adjacent to epithelial thickness changes were found. Microbiological studies investigated the effect of epithelial changes on corneal susceptibility to bacterial infections by exposing OK-treated corneas to large amounts of Pseudomonas aeruginosa. The hypothesis that OK lenses increased susceptibility to infection (within the time tested) was rejected as no infections were produced in any animals (except the positive scratch control). Length of OK treatment, duration and quantity of bacterial exposure, lens wearing schedule and bacterial strain type did not affect susceptibility to infection. The epithelium is a major contributor to OK-induced corneal changes. These epithelial changes are reversible and do not appear to predispose to infection provided corneal integrity is maintained.

Aim: This study looks at the effect of orthokeratology on a number of biometric parameters and refractive error in an adult population. Method: Forty three myopic subjects were recruited to a twelve month study into the effects of orthokeratology on ocular biometry and refractive error. Two different back surface lens designs were applied right eye) pentacurve and left eye) aspheric. The aspheric design was chosen to more closely mimic the cornea's natural shape. Anterior and posterior apical radii and p-values; corneal thickness and anterior chamber depth were measured using the Orbscan IIz; together with ocular biometry by IOL Master and a standard clinical refraction. All measurements were repeated at one night, one week, one, three, six and twelve months. Refractive changes were analysed against biometric changes. Results: Twenty seven participants completed one month of lens wear. Twelve subjects completed twelve months of lens wear. Subjects with myopia ≤ -4.00DS were successfully treated with orthokeratology. Both anterior and posterior apical radii and p values were altered by orthokeratology. Corneal thickness changes were in agreement with previously published studies. Axial length and anterior chamber depth were unaffected by the treatment. Conclusion: Orthokeratology should be available as an alternative to laser refractive surgery. It is best restricted to myopes of up to -4.00DS with low levels of with the rule corneal astigmatism. The use of an aspheric back design contact lens did not produce a significant benefit over that of a pentacurve.

The purpose of this thesis was to investigate age related variations in anterior ocular characteristics and their effect on the response to short-term (one-hour) open eye orthokeratology (OK) lens wear and overnight hydrogel lens wear. Sixty-three volunteer subjects were divided into three groups comprising children (Group I), young adults (Group II) and older adults (Group III). Anterior ocular characteristics that were measured included corneal topography with the Medmont corneal topographer, total, stromal and epithelial thickness with the Holden-Payor optical pachometer, microscopic cell characteristics with the confocal microscope, corneal aesthesiometry, corneal modulus of elasticity, and tear film, palpebral and eyelid characteristics. The older cornea was found to be more spherical in shape (asphericity Q = -0.24 ?? 0.07 in group III compared to -0.34 ?? 0.09 and -0.32 ?? 0.17 in groups I and II respectively) and showed a tendency from with-the-rule to against-the-rule astigmatism. Older subjects also had a decreased endothelial cell density (2596 ?? 111 cells/mm2 in group III compared to 2793 ?? 138 cells/mm2 in group II) and reduced eyelid tension compared to the younger groups. Children were found to have lower blink rates than adults. It was concluded that these changes might have a significant impact on contact lens wear. The responses to two contact lens based techniques, orthokeratology (OK) and hydrogel overnight wear (ON), were studied. Sixty subjects (20 per group) wore reverse-geometry lenses (BE, Ultravison Aust Pty Ltd) of Boston XO material in one eye under open eye conditions for one hour in one eye only. Changes in unaided visual acuity, corneal curvature, corneal thickness and confocal microscopic variables were measured after OK lens wear. All subject groups showed statistically significant improvements (p < 0.05) in unaided visual acuity, a trend for more positive (less prolate) corneal asphericity, increase in apical corneal radius and decrease in central total corneal thickness, after OK lens wear. When the groups were stratified, statistical significance was obtained between the older group and the other two younger groups for change in apical corneal radius (0.23 ?? 0.01 mm in group I, 0.15 ?? 0.01 mm for group II, 0.06 ?? 0.33 for group III). The change in asphericity also showed significant differences between the older age group (0.10 ?? 0.08 mm) and the young adult group (0.21 ?? 0.13). Central corneal thinning obtained after one hour of OK lens wear revealed significant differences between the older adult group (-1.9 ?? 3.2 ??m) and the other two groups (-5.0 ?? 5.9 ??m in group I, -5.0 ?? 2.0 ??m for group II). Sixty subjects wore hydrogel lenses (One-Day Acuvue, Johnson and Johnson Visioncare Pty Ltd) made of etafilcon A in one eye only overnight during sleep at their home. Changes in unaided visual acuity, corneal curvature, corneal thickness, confocal microscopic variables and slitlamp variables were measured after ON lens wear. All subjects showed significant thickening (p < 0.05) of the cornea with ON wear, more in the lens-wearing eye. This study reported that the edema response induced by Acuvue contact lenses is stromal in origin. The edema response of the older group (33.9 ?? 11.5 ??m) was lower than the other two groups as demonstrated by the difference in the change in central stromal thickness (49.3 ?? 20.3 ??m for group I and 51.0 ?? 20.0 ??m for group II). However, a statistically significant difference in the change in thickness was not reached either for the central total corneal thickness or for other topographic locations. Corneal and visual changes found in this study confirm previous reports of the effects of short term OK and hydrogel ON lens wear. Older lens wearers showed a reduced or delayed response to short-term lens wear. Studies investigating the effects of age with long lens-wearing durations are warranted to quantify these effects further.

Introduction: Quite new on the Swedish market are orthokeratology lenses, used for both correction and myopia control. At the moment there are 22 practitioners in Sweden fitting orthokeratology lenses and 5 of those stands for 75 % of all fittings. Measuring the intraocular pressure in the eye is an important part of an eye- examination, because high intraocular pressure can result in glaucomatous changes. When using the orthokeratology lenses the corneal thickness changes, it decreases in the central epithelium and increases in the midperipheral stroma. The corneal thickness is affecting the intraocular pressure value.

Aim: The aim of the study was to evaluate how the intraocular pressure, measured with a non-contact tonometer, changes when using orthokeratology lenses.

Method: 7 people were fitted with orthokeratology lenses. The intraocular pressure was measured before using the lenses, after the first night, after the third night and after the seventh night. 12 eyes were measured after the tenth night, because of drop- out of two eyes.

Result: Already after the first night a significant decrease in the intraocular pressure occurred with 1, 34 mm Hg (p= 0,049). Day ten the intraocular pressure had an average decrease of 2, 67 ± 2, 14 mm Hg, which was a significant change (p= 0, 002 ).

Discussion: This study shows when wearing orthokeratology lenses a decrease in 2, 67 ± 2, 14 mm Hg at day 10 can be expected.

Although there is considerable published research on the efficacy and corneal response to orthokeratology (OK) lenses that flatten corneal curvature to correct myopia, the effects of OK lenses that attempt to steepen corneal curvature to correct hyperopia are poorly understood. This project investigated the effects of hyperopic OK lens wear on corneal shape, refraction and vision. Open-eye and closed-eye overnight studies were conducted with proprietary hyperopic OK lenses, and these led to the development of an experimental hyperopic OK lens design which allowed manipulation of individual lens design parameters. Changes to refraction and best corrected visual acuity (BCVA), corneal topography (Medmont E300), and the profile of total and stromal corneal thickness (Holden-Payor optical pachometer) were measured over periods up to one week of overnight lens wear. Most refractive change occurred after the first night of wear, with increasing effect towards one week. Retention of effect at the end of the day increased with more nights of lens wear. BCVA decreased with longer periods of lens wear. Greater inter-subject variability in effect was found with higher refractive targets. The central cornea steepened and para-central cornea flattened producing a central steepening zone (CSZ) surrounded by a para-central annular flattened zone. CSZ diameter reduced with longer periods of lens wear, and this was significantly associated with decreases in high and low contrast BCVA. There was no change in central corneal thickness beyond the normal overnight lens induced hypoxic edema response. Once edema had resolved thinning of the para-central corneal epithelium was found which resulted in an overall thinning of the para-central cornea. Although central lens fenestrations did not affect the hyperopic OK response, a stronger relationship between changes to apical corneal curvature and refraction resulted. This supports the conclusion that the hyperopic OK effect is due to molding of the corneal surface towards alignment with the lens back surface. Similarities to the pattern of clinical change in myopic OK suggest that a similar corneal molding mechanism occurs in myopic OK. BCVA loss prevented longer term studies and needs to be resolved if hyperopic OK is to become established as a viable clinical technique.

Orthokeratology (OK) contact lenses have shown propensity for slowing down the worsening of myopia in children and young adults, with only some understanding of the mechanism. This thesis examined eye muscle coordination and focussing in OK contact lens wear; outcomes were consistent with a lower myopia progression risk and improved visual comfort compared to standard spectacles and soft contact lenses. These findings have relevance for patient acceptance, clinical management protocols and understanding OK's optical impact on the visual system of the young myope.

This thesis has investigated nearwork-induced transient myopia and accommodation responses in relation to refractive stability, multichromatic stimuli and orthokeratology. Five individual studies have been carried out. Initially an investigation into the temporal and dioptric aspects of nearwork-induced transient myopia was undertaken, suggesting that increased task duration does not increase the level, or slow the regression of post-task NITM, however an increase in the dioptric demand of the task does. In the second study, a longitudinal myopia progression study, these findings were related to short term myopia progression. The third investigation demonstrates the feasibility of measuring the biometric correlates of nearwork-induced transient myopia using a low coherence reflectometry device (LenStar, Haag Streit Koeniz, Switzerland). Fourthly, a comparison of the differences between static and dynamic accommodative responses, microfluctuations and nearwork-induced transient myopia produced when viewing a black/white target as oppose to a red/blue target has suggested the possibility of four accommodative responses to this multichromatic stimulus. Further investigation will be necessary to investigate if any of these response types are related to myopia progression. 2 The final study investigates the effect of two different designs of orthokeratology contact lenses (C5 and polynomial) on visual function. It appears to be the case that although the polynomial lens design has a larger refractive effect than the C5 lens it reduces both high and low contrast corrected visual acuity to a greater extent. The higher the baseline mean spherical equivalent refractive error the larger the detrimental effect.
College of Optometrists

Purposes: To use optical coherence tomography (OCT) to image and quantify the effect of various corneal conditions, in terms of corneal, stromal and epithelial thickness, and light backscatter. To assess the changes caused by overnight orthokeratology (Corneal Refractive Therapy; CRT^TM) lens wear, keratoconus and laser in-situ keratomileusis (LASIK) refractive surgery, each of which may lead to topographical alterations in corneal thickness either by temporary moulding, degeneration, or permanent laser ablation, respectively.

Methods: Topographical thickness of the cornea was measured using OCT in all studies. The CRT^TM studies investigated myopic and hyperopic treatment, throughout the day. The myopic studies followed lens wear over a 4 week period, which was extended to 12 months, and investigated the thickness changes produced by two lenses of different oxygen transmissibility. CRT^TM for hyperopia (CRTH^TM) was evaluated after a single night of lens wear.

In the investigation of keratoconus, OCT corneal thickness values were compared to those obtained from Orbscan II (ORB) and ultrasound pachymetry (UP). A new fixation device was constructed to aid in the measurement of topographical corneal and epithelial thickness along 8 directions of gaze. Pachymetry maps were produced for the normal non-lens wearing cornea, and compared with the rigid gas permeable (RGP) lens wearing cornea and the keratoconic cornea.

Thickness changes prior to, and following LASIK were measured and monitored throughout six months. Myopic and hyperopic correction was investigated individually, as the laser ablation profiles differ for each type of procedure. The LASIK flap interface was also evaluated by using light backscatter data to monitor healing.

Results: Following immediate lens removal after myopic CRT^TM, the central cornea swelled less than the periphery, with corneal swelling recovering to baseline levels within 3 hours. The central epithelium decreased and mid-peripheral epithelium increased in thickness, with a more gradual recovery throughout the day. There also seemed to be an adaptation effect on the cornea and epithelium, showing a reduced amount of change by the end of the 4 week study period. The thickness changes did not alter dramatically during the 12 month extended study. In comparing the two lens materials used for myopic CRT^TM (Dk/t 91 vs. 47), there were differences in stromal swelling, but no differences in the central epithelial thinning caused by lens wear. There was a statistically insignificant asymmetry in mid-peripheral epithelial thickening between eyes, with the lens of lower Dk causing the greater amount of thickening. Hyperopic CRT^TM produced a greater increase in central stromal and central epithelial thickness than the mid-periphery. Once again, the stroma recovered faster than the epithelium, which remained significantly thicker centrally for at least six hours following lens removal.

Global pachymetry measurements of the normal cornea and epithelium found the periphery to be thicker than the centre. The superior cornea and epithelium was thicker than the inferior. In the measurement of the keratoconic cornea, OCT and ORB correlated well in corneal thickness values. UP measured greater values of corneal thickness. The keratoconic epithelium was thinner than normal, and more so over the apex of the cone than at the centre. The location of the cone was most commonly found in the inferior temporal region. Central epithelial thickness was thinner in keratoconics than in RGP lens wearers, which in turn was thinner than in non-lens wearers.

Following LASIK surgery for both myopia and hyperopia, the topographical OCT thickness profiles showed stromal thinning in the areas of ablation. The central myopic cornea showed slight regression at 6 months. During early recovery, epithelial thickness increased centrally in hyperopes and mid-peripherally in myopes. By the end of the 6 month study, mid-peripheral epithelial thickness was greater than the centre in both groups of subjects. The light backscatter profiles after LASIK showed a greater increase in backscatter on the anterior side of the flap interface (nearer the epithelium), than the posterior side (in the mid-stroma) during healing. The flap interface was difficult to locate in the OCT images at 6 months.

Conclusion: All the CRT^TM lenses used in this project produced more corneal swelling than that seen normally overnight without lens wear. In order for these lenses to be worn safely for long periods of time without affecting the health of the cornea, they need to be manufactured from the highest oxygen transmissible material available. The long-term effect of thinning on the epithelium's barrier properties needs to be monitored closely.

Global topographical thickness of the cornea and epithelium was measured using OCT in normal, RGP lens wearing and keratoconic eyes. Corneal and epithelial thickness was not symmetrical across meridians. The epithelium of RGP lens wearers was slightly thinner than normal, but not as thin as in keratoconics, suggesting that the epithelial change seen in keratoconus is mainly due to the condition.

Post-LASIK corneal and epithelial thickness profiles were not the same for myopic and hyperopic subjects, since the ablation patterns vary. Epithelial thickening in the mid-periphery had not recovered by six months in myopes or hyperopes, possibly indicating epithelial hyperplasia. Light backscatter profiles were used to monitor the recovery of the LASIK flap interface, showing the band of light backscatter around the flap interface to decrease as the cornea healed.

This thesis has investigated nearwork-induced transient myopia and accommodation responses in relation to refractive stability, multichromatic stimuli and orthokeratology. Five individual studies have been carried out. Initially an investigation into the temporal and dioptric aspects of nearwork-induced transient myopia was undertaken, suggesting that increased task duration does not increase the level, or slow the regression of post-task NITM, however an increase in the dioptric demand of the task does. In the second study, a longitudinal myopia progression study, these findings were related to short term myopia progression. The third investigation demonstrates the feasibility of measuring the biometric correlates of nearwork-induced transient myopia using a low coherence reflectometry device (LenStar, Haag Streit Koeniz, Switzerland). Fourthly, a comparison of the differences between static and dynamic accommodative responses, microfluctuations and nearwork-induced transient myopia produced when viewing a black/white target as oppose to a red/blue target has suggested the possibility of four accommodative responses to this multichromatic stimulus. Further investigation will be necessary to investigate if any of these response types are related to myopia progression. 2 The final study investigates the effect of two different designs of orthokeratology contact lenses (C5 and polynomial) on visual function. It appears to be the case that although the polynomial lens design has a larger refractive effect than the C5 lens it reduces both high and low contrast corrected visual acuity to a greater extent. The higher the baseline mean spherical equivalent refractive error the larger the detrimental effect.

Aberrations affect image quality of the eye away from the line of sight as well as along it. High amounts of lower order aberrations are found in the peripheral visual field and higher order aberrations change away from the centre of the visual field. Peripheral resolution is poorer than that in central vision, but peripheral vision is important for movement and detection tasks (for example driving) which are adversely affected by poor peripheral image quality. Any physiological process or intervention that affects axial image quality will affect peripheral image quality as well. The aim of this study was to investigate the effects of accommodation, myopia, age, and refractive interventions of orthokeratology, laser in situ keratomileusis and intraocular lens implantation on the peripheral aberrations of the eye. This is the first systematic investigation of peripheral aberrations in a variety of subject groups. Peripheral aberrations can be measured either by rotating a measuring instrument relative to the eye or rotating the eye relative to the instrument. I used the latter as it is much easier to do. To rule out effects of eye rotation on peripheral aberrations, I investigated the effects of eye rotation on axial and peripheral cycloplegic refraction using an open field autorefractor. For axial refraction, the subjects fixated at a target straight ahead, while their heads were rotated by ±30º with a compensatory eye rotation to view the target. For peripheral refraction, the subjects rotated their eyes to fixate on targets out to ±34° along the horizontal visual field, followed by measurements in which they rotated their heads such that the eyes stayed in the primary position relative to the head while fixating at the peripheral targets. Oblique viewing did not affect axial or peripheral refraction. Therefore it is not critical, within the range of viewing angles studied, if axial and peripheral refractions are measured with rotation of the eye relative to the instrument or rotation of the instrument relative to the eye. Peripheral aberrations were measured using a commercial Hartmann-Shack aberrometer. A number of hardware and software changes were made. The 1.4 mm range limiting aperture was replaced by a larger aperture (2.5 mm) to ensure all the light from peripheral parts of the pupil reached the instrument detector even when aberrations were high such as those occur in peripheral vision. The power of the super luminescent diode source was increased to improve detection of spots passing through the peripheral pupil. A beam splitter was placed between the subjects and the aberrometer, through which they viewed an array of targets on a wall or projected on a screen in a 6 row x 7 column matrix of points covering a visual field of 42 x 32. In peripheral vision, the pupil of the eye appears elliptical rather than circular; data were analysed off-line using custom software to determine peripheral aberrations. All analyses in the study were conducted for 5.0 mm pupils. Influence of accommodation on peripheral aberrations was investigated in young emmetropic subjects by presenting fixation targets at 25 cm and 3 m (4.0 D and 0.3 D accommodative demands, respectively). Increase in accommodation did not affect the patterns of any aberrations across the field, but there was overall negative shift in spherical aberration across the visual field of 0.10 ± 0.01m. Subsequent studies were conducted with the targets at a 1.2 m distance. Young emmetropes, young myopes and older emmetropes exhibited similar patterns of astigmatism and coma across the visual field. However, the rate of change of coma across the field was higher in young myopes than young emmetropes and was highest in older emmetropes amongst the three groups. Spherical aberration showed an overall decrease in myopes and increase in older emmetropes across the field, as compared to young emmetropes. Orthokeratology, spherical IOL implantation and LASIK altered peripheral higher order aberrations considerably, especially spherical aberration. Spherical IOL implantation resulted in an overall increase in spherical aberration across the field. Orthokeratology and LASIK reversed the direction of change in coma across the field. Orthokeratology corrected peripheral relative hypermetropia through correcting myopia in the central visual field. Theoretical ray tracing demonstrated that changes in aberrations due to orthokeratology and LASIK can be explained by the induced changes in radius of curvature and asphericity of the cornea. This investigation has shown that peripheral aberrations can be measured with reasonable accuracy with eye rotation relative to the instrument. Peripheral aberrations are affected by accommodation, myopia, age, orthokeratology, spherical intraocular lens implantation and laser in situ keratomileusis. These factors affect the magnitudes and patterns of most aberrations considerably (especially coma and spherical aberration) across the studied visual field. The changes in aberrations across the field may influence peripheral detection and motion perception. However, further research is required to investigate how the changes in aberrations influence peripheral detection and motion perception and consequently peripheral vision task performance.

The first papers on the fitting of ortho-k lenses in ametropic individuals, treatment that allows them to enjoy good vision without the need to wear glasses or contact lenses, were published almost 60 years ago. Both the reversibility of the treatment when the lenses are discontinued, as well as the slight loss of the effect suffered by users throughout the day have been studied, but there is no paper to date that justifies or foresees diurnal regression based on corneal biomechanical properties provided by the Corvis ST® tonometer. OBJECTIVES: To assess how the corneal and visual parameters vary throughout the day, in the short and medium term, after having slept with orthokeratology lenses, and relate them to the baseline data of visual acuity, refraction, topographic and biomechanical properties, in this way, to help clinicians make a better prognosis in front of a potential orthokeratology treatment. We also wanted to verify whether the parameters related to corneal biomechanics vary after orthokeratology treatment. METHODS: 75 adults with myopia between -0.50 and -5.00 D with a corneal and refractive astigmatism lower than -1.25 D, were recruited to be fitted at the Center Universitari de la Visió (FOOT-UPC) with Seefree® orthokeratology lenses (Conóptica - Hecht Contactlinsen), spherical or toric, as required by each individual. Baseline measurements of LogMAR visual acuity, refraction, corneal tomography (Pentacam®), corneal biomechanics (Corvis ST®) and intraocular pressure (CT-80®) were performed. After starting to sleep with the orthokeratology lenses, the same measurements were repeated after the first night of use, after one week and after three months, twice a day, one in the morning and one in the afternoon, 8 hours apart between both visits. RESULTS: 69 patients reached the weekly control and 49 the quarterly. None of the dropouts responded to severe complications. A mean diurnal regression of 0.25 D was found throughout the day at all moments evaluated. Only a slight statistically significant relationship was found between the baseline refraction and the diurnal refractive regression in the quarterly control (R2=0.099 p=0.015). After ortho-k, the cornea shows greater rigidity in the morning that decreases during the day, while the changes in curvature in both the anterior and posterior cornea throughout the day were similar to those suffered by non-users of orthokeratology. Baseline values of anterior corneal asphericity, corneal biomechanics, pachymetry and intraocular pressure were not predictive of orthokeratology success or diurnal regression. Regarding topography, it was only observed that the smaller the anterior corneal steep radius, the greater the orthokeratology effect (¿=-0.431 p=0.002). The biomechanically adjusted intraocular pressure did not show variations throughout the study. The changes found after orthokeratology in corneal biomechanics seem to be more related to the pachymetry change than due to a modification of corneal stiffness. CONCLUSIONS: The biomechanical parameters provided by Corvis ST® do not predict the corneal response to ortho-k. Smaller anterior steep corneal radii seem to favour the orthokeratology effect. Corneal biomechanics does not seem to be affected by orthokeratology, although some Corvis ST® parameters do change, because they are influenced by pachymetry variations and this is a well-known effect after orthokeratology. Intraocular pressure is not affected by orthokeratology treatment when it is biomechanically compensated. These results provide security to the eye care practitioners in their clinical practice regarding concerns about a possible negative impact of the orthokeratology effect on corneal biomechanics in the short and medium term.
Fa quasi 60 anys de les primeres publicacions sobre l'adaptació de lents d'orto-k en individus ametrops, tractament que els permet gaudir d'una bona visió sense la necessitat de fer servir ulleres o lents de contacte. Hi ha estudis tant sobre la seva reversibilitat refractiva al deixar de fer servir les lents, com de la lleu perduda d'efecte que pateixen els usuaris al llarg del dia, però cap a dia d'avui que justifiqui o prevegi la regressió diürna en funció de les propietats biomecàniques corneals aportades pel tonòmetre Corvis ST®. OBJECTIUS: Avaluar com varien els paràmetres corneals i visuals al llarg del dia, a curt i mitja terme, després d'haver dormit amb lents d'ortoqueratologia i relacionar-los amb les dades de partida d'agudesa visual, refractius, topogràfics i biomecànics, per d'aquesta forma, ajudar als clínics a realitzar un millor pronòstic davant un potencial tractament ortoqueratològic. També es va voler comprovar si els paràmetres relatius a la biomecànica corneal varien després del tractament ortoqueratològic. MÈTODES: 75 adults amb miopies entre -0,50 i -5,00 D i amb un astigmatisme refractiu i corneal inferior a -1,25 D van ser reclutats per ser adaptats al Centre Universitari de la Visió (FOOT-UPC) amb lents d'ortoqueratologia Seefree® (Conóptica Hecht Contactlinsen), esfèriques o tòriques segons requerís cada individu. Es van fer mesures basals d'agudesa visual LogMar, refracció, tomografia corneal (Pentacam®), biomecànica corneal (Corvis ST®) i pressió intraocular (CT-80®). En començar a dormir amb les lents d'ortoqueratologia es van repetir les mateixes mesures després de la primera nit d'us, a la setmana i als tres mesos, dues vegades al dia, una al matí i una altra a la tarda, amb 8 hores de diferència entre ambdues visites. RESULTATS: 69 pacients van arribar al control setmanal i 49 al trimestral. Cap dels abandonaments va respondre a complicacions severes. Es va trobar una regressió diürna mitja de 0,25 D al llarg del dia a tots els moments avaluats. Únicament es va trobar una lleu relació estadísticament significativa entre el valor de la refracció basal i la regressió refractiva diürna al control trimestral (R2=0,099 p=0,015). Després de l'orto-k, pel matí, les còrnies presenten una major rigidesa que va disminuint durant el dia, mentre que els canvis de curvatura tant en cara anterior com posterior corneals, son similars als mostrats per no usuaris d'ortoqueratologia. Els valors basals d'asfericitat corneal anterior, biomecànica corneal, paquimetria i pressió intraocular no van ser predictius de l'èxit ortoqueratològic ni de la regressió diürna. Pel que fa a la topografia, únicament es va observar que quant menor va ser el radi tancat corneal anterior major va ser l'efecte ortoqueratològic (¿=-0,431 p=0,002). La pressió intraocular ajustada biomecànicament no va mostrar variacions al llarg de l'estudi. Els canvis trobats després d'ortoqueratologia a la biomecànica corneal estarien més relacionats amb el canvi paquimètric que no pas amb una afectació de la rigidesa corneal. CONCLUSIONS: Els paràmetres biomecànics aportats per Corvis ST® no prediuen la resposta corneal a l'orto-k. Radis corneals anteriors més tancats semblen afavorir l'efecte ortoqueratològic. La biomecànica corneal no sembla estar afectada per l'ortoqueratologia, encara que alguns paràmetres de Corvis ST® sí ho estan, degut a que, estan influenciats pels canvis paquimètrics, i aquest és un conegut efecte de l'ortoqueratologia. La pressió intraocular no està afectada pel tractament ortoqueratològic quan es compensa biomecànicament. Aquests resultats aporten seguretat als adaptadors a la seva pràctica clínica davant inquietuds vers una possible afectació negativa de l'efecte ortoqueratològic en la biomecànica corneal a curt i mitjà terme.
Hace ya casi 60 años de las primeras publicaciones sobre la adaptación de lentes de orto-k en individuos amétropes, tratamiento que les permite gozar de una buena visión sin la necesidad de usar gafas o lentes de contacto. Hay estudios tanto sobre la reversibilidad refractiva al dejar de usar las lentes, como de la leve pérdida de efecto que sufren los usuarios a lo largo del día, pero ninguno a día de hoy que justifique o prevea la regresión diurna en función de las propiedades biomecánicas corneales aportadas por el tonómetro Corvis ST®. Evaluar cómo varían los parámetros corneales y visuales a lo largo del día, a corto y medio plazo, después de haber dormido con lentes de ortoqueratología, y relacionarlos con los datos de partida de agudeza visual, refractivos, topográficos y biomecánicos, para de esta forma, ayudar a los clínicos a realizar un mejor pronóstico frente un potencial tratamiento ortoqueratológico. También se quiso comprobar si los parámetros relativos a la biomecánica corneal varían tras el tratamiento ortoqueratológico. 75 adultos con miopías entre -0,50 y -5,00 D y con un astigmatismo refractivo y corneal inferior a -1,25 D, fueron reclutados para ser adaptados en el Centre Universitari de la Visió (FOOT-UPC) con lentes de ortoqueratología Seefree® (Conóptica - Hecht Contactlinsen), esféricas o teóricas, según requiriese cada individuo. Se realizaron medidas basales de agudeza visual LogMAR, refracción, tomografía corneal (Pentacam®), biomecánica corneal (Corvis ST®) y presión intraocular (CT-80®). Tras empezar a dormir con las lentes de ortoqueratología se les repitieron las mismas mediciones tras la primera noche de uso, a la semana y a los tres meses, dos veces cada día, una por la mañana y otra por la tarde, con 8 horas de diferencia entre ambas visitas. 69 pacientes llegaron al control semanal y 49 al trimestral. Ninguno de los abandonos respondió a complicaciones severas. Se encontró una regresión diurna media de 0,25 D a lo largo del día en todos los momentos evaluados. Únicamente se encontró una leve relación estadísticamente significativa entre el valor de la refracción basal y la regresión refractiva diurna en el control trimestral (R2=0,099 p=0,015). Tras la orto-k, por la mañana, las córneas presentan una mayor Caracterización de la Regresión Diurna con Ortoqueratología rigidez que va disminuyendo durante el día, mientras que los cambios de curvatura tanto en cara anterior como posterior corneal a lo largo del día, son similares a los que sufren no usuarios de ortoqueratología. Los valores basales de asfericidad corneal anterior, biomecánica corneal, paquimetría, y presión intraocular no fueron predictivos del éxito ortoqueratológico ni de la regresión diurna. En cuanto a la topografía, únicamente se observó que cuanto menor fue el radio cerrado corneal anterior, mayor fue el efecto ortoqueratológico (ρ=-0,431 p=0,002). La presión intraocular ajustada biomecánicamente no mostró variaciones a lo largo del estudio. Los cambios hallados tras ortoqueratología en la biomecánica corneal estarían más relacionados con el cambio paquimétrico que con una afectación a la rigidez corneal. Los parámetros biomecánicos generados por Corvis ST® no predicen la respuesta corneal a la orto-k. Radios corneales anteriores más cerrados parecen favorecer el efecto ortoqueratológico. La biomecánica corneal no parece estar afectada por la ortoqueratología, aunque algunos parámetros de Corvis ST® sí lo están debido a que, están influenciados por los cambios paquimétricos, y este es un efecto conocido de la ortoqueratología. La presión intraocular no está afectada por el tratamiento ortoqueratológico cuando se compensa biomecánicamente. Estos resultados aportan seguridad a los adaptadores en su práctica clínica frente a inquietudes sobre una posible afectación negativa del efecto ortoqueratológico en la biomecánica corneal a corto y medio plazo.
Enginyeria òptica

碩士
中臺科技大學
醫學工程暨材料研究所
100
Purpose. Orthokeratology (OK) is a clinical technique that uses specially designed rigid contact lenses to reshape the cornea to temporarily reduce or eliminate refractive error.This study is aimed to evaluate the quality of life post overnight orthokeratology. Methods. Patients were randomly selected from consecutive cases among the clinic population who undergo orthokeratology after one year.All subjects were free from diseases such as keratoconus, glaucoma, diabetes mellitus, and history of previous contact lens wear, ocular surgery, ocular trauma and family history of ocular disease. Questionnaire data will be obtained during treatment after agreeing participates in this study. Data will be analyzed after questionnaire collection. Conclusions. The users who undergo orthokeratology and their parents have high level of quality of life and the correlations between factors of user and their parents are significant.

碩士
中臺科技大學
醫學工程暨材料研究所
104
Purpose. The purpose of this study is discussing orthokeratology trial lens pollution in used over period of time, and to understand the degree of microbial contamination effects by number amount times. Methods. This study collects orthokeratology trial lenses which have been worn for 1 year (N=77). The PBS ( Phosphate buffered saline ) was used to sample the inner surface to collect bacteria. Bacteria solution onto BAP、CAP、SDA incubate at 37 ° C in an atmosphere containing 5% CO2 for 48 hours. Results. Of the 77 samples, 68 (88.3%) were sterile, whereas 9 (11.7%) were contaminated with at least 1 of the isolated microbes. We found CNS, Acinetobacter, Flavobacteriaceae, Rhizobium, Fungi. In 5 (6.5%) were contaminated with 1 microbes, 1 (1.3%) were contaminated with 2 microbes, 3 (3.9%) were contaminated with 4 microbes. In the contamination and tried orthokeratology trial lenses has a number of uses no significant difference (P=0.768). Conclusion. The orthokeratology trial lens of the microbial contamination will not cause by use of high frequency. It depends on whether to comply with the program of the lens care routines, if the omission of the lens care is still cause by microbial contamination is one of the main factor. Key words: orthokeratology、orthokeratology trial lens、trial lens、microbial contamination

碩士
中臺科技大學
視光產業碩士專班
102
The main purpose of this study was to investigate the potential relationship between biomechanical properties of the cornea ( corneal hysteresis and corneal resistance factor) and the visual performance after using orthokeratology correction on young people. The data was collected from Taipei Daan B&B Eye clinic from February to December 2013. 35 juvenile myopia patients (65 eyes, 24 males and 11 females) was recruited and the average age was 12.5 ± 3.3 years old, range from 7.5 to 25.4 years old. The mean spherical equivalent is -3.18 ± 1.50D and the spherical equivalent range from -1.13D to -7.13D. All the participants have not worn any contact lenses before this research and are all free from eye diseases nor contraindications to contact lens wear. The orthoK lens design we used was Dreimlens from Hiline corporation ( DOH Medical device manufacture Zi No. 002921) Before dispensing, corneal characteristics (CH and CRF) were measured with the Reichert Ocular Response Analyzer, Goldmann IOP and corneal compensated IOP. All the data was analyzed with the SPSS 17.0 statistical software. To avoid corneal biomechanical properties between the eyes with a relevant case , we use only the left eye’s data for statistical analysis , P <0.05 was considered statistically significant. The results from this study was shown that there is no statistically significant relationship between biomechanical properties of the cornea and the visual performance after using orthokeratology correction.

碩士
中山醫學大學
生物醫學科學學系碩士班
102
In Taiwan, the percentage of myopia has reached as high as 62%. The current control myopia methods include bifocal spectacle lenses, progressive spectacle lenses, soft bifocal contact lenses, biological agents such as atropine and pirenzepine as well as orthokeratology (Ortho-K).Ortho-K provides clear vision despite of not wearing lenses during daytime. The Ortho-K has been proven to be effective in terms of delaying the development of myopia, but the mechanism behind it still awaits further clarification. The purpose of this study is to evaluate the changes of refractive error in the children who were prescribed with Ortho-K, at the same time to seek for the factors that affect the result of Ortho-K wear. By comparing the refractive values before prescribing Ortho-K and the values 6 years after wearing Ortho-K, find the relationship between the two and then determine the factors that lead to retarding myopia progression of Ortho-K wear. This study analyze52 children of age between 12-18 whom were prescribed with Ortho-K for 6 years, where this selected children have myopia of less than -4.00 D and astigmatism of less than -1.50 D. The data are compared between the basic parameters such as gender, age, spherical equivalent refractive, keratometry and corneal eccentricity with the changes in refractive error. The result shows that after prescription, the females of age 12-18 have better myopic control than the males and the higher the refractive error prior to prescription of Ortho-K, the lesser the change in refractive error after prescription. Age, corneal curvature corneal and eccentricity do not affect the changes in refractive error. According to the result, Ortho-K is more related to factors such as gender, age, initial refractive error and corneal curvature.

碩士
嘉南藥理大學
藥學系
107
OrthoKeratology lens, or OrthoK, is an anti-geometric hard contact lens. It is worn before going to bed then can be maintained high quality vision during daytime removal. Therefore, it is a good way to clinically control myopia. The purpose of this retrospective study was to evaluate the effect of wearing OrthoK lenses on corneal curvature, visual acuity, and spherical equivalents. Eighty-five subjects in the experimental group were included routine eyesight examination without any eye disease, myopia was between -0.50 D and -6.50 D, astigmatism was between -0.50 D~-2.00 D, and 7 to 16 years old had OrthoK lenses. Another thirty subjects in the control group were wearing traditional glasses. Comparing the degree of myopia control in the two groups for more than 3 years, after the first day, the first week, the third month, the sixth month, the first year, the third year with wearing lenses, and two weeks after the OrthoK lenses were removed. The changes of corneal curvature, visual acuity and spherical equivalents were analyzed and compared by Pair-T test and ANOVA test. The results showed that compared with the baseline, regardless of the degree of myopia, there was a significant difference in visual acuity, spherical equivalents, and corneal curvature after one day with wearing OrthoK lenses (P<0.05), which indicate that the OrthoK lenses were worn for one day can improve vision. However, after OrthoK lenses treatment for one month, the changed degree of spherical surface of the low-degree myopia was slowly, indicating that the effect of improving vision has stabilized. The height of myopia was changed lowly after 6 months OrthoK treatment (P<0.05), indicating that the height of myopia requires a longer time to stabilize. Therefore, the final measurement of the spherical equivalents has a significant correlation with the initial myopia. Inferred from the results of this retrospective study: wearing OrthoK lenses for the treatment of myopia can significantly reduce the degree of myopia after wearing and corneal curvature changes from the central to the periphery, continuous shaping can provide stable and good naked vision during the day. After two weeks of wearing the OrthoK lenses, there was no significant difference between the corneal curvature and the initial corneal curvature, indicating that the cornea was not irreversible damage due to long-term molding. Therefore, for students with myopia, wearing OrthoK lenses is an option to consider.

碩士
中山醫學大學
生物醫學科學學系碩士班
104
Background: According to the statistics, the prevalence level of myopia has reached over 90% of the population in Taiwan. The methods of control myopia include Atropine, multifocal spectacle, and overnight orthokeratology. Orthokeratology is a temporally non-surgical correction of refractive errors. The special design of orthokeratology lens can offset the patient’s refractive error when patient sleep. Due to the lens design, cornea is reshaped and thickness changed. Cornea reshaping causes the thickness changes in central and peripheral region and thus inducing high order aberration. Purpose: In this study, we will investigate the change of corneal central and peripheral thickness and ocular high order aberration associate with overnight orthokeratology. Methods: This analysis is a retrospective study of patients with myopia who had undergone Ortho-K treatment. Before the treatment, patients would receive a comprehensive ocular-visual examination; it includes the refractive errors, best visual acuity, corneal curvature, corneal eccentricity, topography and Wavefront aberration. Patients were examined before OK treatment,7 days and 30 days post lens wearing. Each examination include slit lamp examination, corneal curvature, lens fitting assessment, fluorescein pattern , refractive errors, best visual acuity, corneal eccentricity, Wavefront aberration, topography and pachymetry. Results: There are 19 subjects, 37 eyes (12 females, 7 males, mean age 11.31 ± 2.27 year-old). Mean spherical equivalent power (SER) is -3.27 ± 1.62 D. Corneal Apex refractive power has significant changed after wearing Ortho-K lens (p < 0.05). Corneal refractive power of nasal 1 mm (N1), temporal 1mm (T1), temporal 2 mm (T2), superior 1 mm (S1) and inferior 1 mm (I1) become significantly flatter after Ortho-K treatment (all p < 0.05). But there are no significant differences in corneal thickness change (p > 0.05). High order aberrations have significantly increased after treatment, especially Spherical aberration (all p < 0.05) and Coma aberration (all p < 0.05). Defocus aberration has significantly decreased after 30 days Ortho-K treatment. The change of Spherical aberration is positively correlated with OK Target Power (p < 0.05), the change of corneal apex refractive power (p < 0.05) and the change of the difference of corneal apex and mid-periphery refractive power (p < 0.05). The change of Coma aberration is significantly correlated with corneal asymmetry (p < 0.05). Conclusion: In this study, it proves ocular high order aberrations will be increased by the corneal reshaping after wearing Ortho-K lens, especially Spherical aberration and Coma aberration. In conclusions, there is a positive correlation between Target Power of orthokeratology and Spherical aberration. Coma aberration is correlated with corneal asymmetry. The more temporal decentration, the more Coma aberration.

碩士
中臺科技大學
醫學工程暨材料研究所
98
Purpose. The ability of resistance to breakage is important for the durability of a contact lens and also the safety of wearer. The aim of this study is to understand the mechanical properties of reverse geometry orthokeratology (OK) lens design when compared with conventional standard (alignment fitted) lens design of the same gas permeable contact lens material. Methods. Reverse geometry orthokeratology and conventional alignment lenses designs with identical back optical zone radius, total diameter, back vertex power, center thickness, edge thickness and lens material were chosen for this comparison study. The flexural strength, flexural deformation at rupture and flexural strength at 30% deformation were measured using the Instron 4301 automated materials testing instrument. Results. The flexural strength at rupture of reverse geometry lenses (369±56 gf) and alignment lenses (339±10 gf) were not significantly different (p=0.465). The flexural deformation at rupture of reverse geometry lenses and alignment lenses were 72±5 % and 73±2 %, respectively, without significant differences as well (p=0.602). However, the flexural strength at 30 % deformation of reverse geometry lenses (121±9 gf) was significantly higher than that of conventional alignment rigid gas permeable lenses (77±3 gf)(p=0.009 ). Conclusions. Reverse geometry orthokeratology lens design showed higher flexural strength at 30 % deformation compared to conventional alignment lens design. This suggest that reverse geometry lens design have less tendency to change its geometric parameters during pressure.

碩士
元培醫事科技大學
生物科技暨製藥技術系碩士班
106
Myopia has been a big problem for the health of Chinese people. High myopia is prone to some complications such as retinal detachment and macular degeneration and glaucoma and cataract. Therefore, it is important to prevent children's myopia from increasing to high myopia. There are two main methods used in Taiwan to slow down and suppress the increase in diopters, namely using mydriatic agent and keratoplasty contact lenses. The mydriatic agent, also known as the ciliary muscle paralysis agents, are parasympathetic blockers. It is to relax the ciliary muscle to slow down the increase of myopia. The orthokeratology lens uses the design of inverse geometric concentric circle to change the shape of the cornea, thereby slowing the progression of myopia. The main purpose of this study was to compare the effectiveness of these two methods in controlling myopia. The project was reviewed and approved by the Human Body Experimental Committee of the Three Military General Hospital. A 5-year backtracking random sampling was use. All the collected datas came from Wanfang Medical Center, Sanjun General Hospital, Banqiao Xinhe Eye Clinic, Danshui Eye Ophthalmology Clinic, and Hsinchu Chen Zhihong Eye Clinic. A total of 1388 eyes were collected, including 738 eyes fitted with Ortho-K lenses (study group) and 650 eyes treated with the Atropine (control group). The age of subjects ranged from 7 to 12 years old. The results showed that the average total myopia and astigmatism increased -0.55D and -0.12D with five years of wearing Ortho-K lenses, and the average increase was -0.11D and -0.02D per year; while the average total myopia and astigmatism increased by -1.75D and -0.38D after five years of using Atropine , with an average annual progression of -0.35D and -0.07D per year. Therefore, The current results indicate either Ortho-K lenses or mydriatic agents can control myopia progression. However, Ortho-K lenses showes better control then Atropine, with the former only 68.58% of the latter。

碩士
元培醫事科技大學
企業管理系碩士班
107
Discussion on the effect of low concentration long-acting mydriatics on myopia control of school children in orthokeratology Student：Shun-Huan Wang Advisor：Che-Yang Lin, Ph. D. Graduate Institute of Business Administration Yuan-pei University of Medical Technology Abstract The prevalence of nearsightedness among schoolchildren in Taiwan is extremely high and rising; the proportion of people who suffer from the high myopia is also increasing, which poses a great threat to the health of national visual acuity. The most effective method of myopia control is currently recognized as corneal casts. However, this study is to investigate whether the use of orthokeratology double with a low concentration of long-acting mydriatics for myopia treatment is more effective than the traditional use of corneal surgery alone. The safety and efficacy of myopic treatment using mydriatic agents or wearing orthokeratology are retrospectively reviewed, too. In this study, 45 children who met the eligibility criteria were collected in the Liming Eye clinic of Zhubei City. Among them, 19 children were treated with orthokeratology and a low concentration long-acting mydriatic eye drops with or below a concentration 0.125% ; another 26 children were only treated with orthokeratology. The data of the degree of myopia, visual acuity and axial length of the school children were measured by the method of two-year regular tracking every six months after the first wearing. The statistical methods such as narrative statistics and repeated measurement variation analysis were used to produce empirical results. The results of the study showed that the growth of the axial length of the children with the orthokeratology plus the low-concentration long-acting mydriatic was significantly smaller. The corneal thickness was significantly thinner after wearing the orthokeratology, but adding the mydriatic agent was not related to the degree of corneal thinning. Two methods of myopia control, the visual acuity of the corrected children were able to reach 0.9 or more, and the correction effect had no significant difference in visual acuity comparison. The study found that school children wearing orthokeratology plus low concentration of long-acting mydriatics would have better myopia control results. This result can be provided to all relevant hospitals, parents, researchers and other related persons as a reference for the schoolchild's control of myopia. Keywords: myopia control, orthokeratology, low concentration long-acting mydriatics, myopic schoolchildren

Dissertação de mestrado em Optometria Avançada
Nos últimos anos tem sido desenvolvidos vários estudos sobre a miopia, tendo como base a sua progressão e as mudanças oculares a ela associada. Desta forma, são várias as técnicas em estudo para controlar a sua progressão. A ortoqueratologia é caracterizada por ser um dos tratamentos óticos que demonstra de forma sistemática a sua efetividade no controlo da progressão da miopia. No entanto, apesar de ser conhecida a sua eficácia, é necessário continuar a identificar os mecanismos (acomodativos, retinianos ou outros) responsáveis pelo efeito provocado. O presente estudo teve como principal objetivo avaliar através da ortoqueratologia as alterações na função acomodativa e, também analisar a mudança da resposta da atividade eletrofisiológica através de exames como o Pattern ERG (PERG) e dos Potenciais Evocados Visuais (PEV) durante dois meses. Registaram-se também ao longo de dois meses as alterações dos seguintes parâmetros visuais: erro refrativo, acuidade visual de alto e baixo contraste, parâmetros topográficos, distorção luminosa e qualidade ótica. Durante este intervalo, foram realizadas seis visitas: Pré-consulta, Baseline, 1 Noite após, 15 Noites após, 30 Noites após e 60 Noites após o tratamento ortoqueratológico. Na pré-consulta obteve-se o erro refrativo do paciente e os parâmetros topográficos. Nas visitas seguintes, foram analisados todos os parâmetros visuais. Exames como o PERG e PEV foram realizados em todas as visitas exceto na pré-consulta. Para a realização deste estudo foram recrutados 10 pacientes (23,20±3,46 anos) com miopias entre -1,00 D e -2,00 D, com um astigmatismo inferior a 1,00 D e sem nenhuma contraindicação para o uso de lentes de contacto. Registou-se a resposta acomodativa através do Autorrefratómetro de Campo Aberto WAM-5500 (GrandSeiko Co, Ltd.) acoplado ao Sistema de Badal, sendo que a vergência do estímulo variou entre 0,00 D (infinito), 1,00 D (1 metro), 2,00 D (50 cms), 3,00 D (33 cms), 4,00 D (25 cms) e 5,00 D (20 cms). Realizaram-se também medidas de eletrofisiológicas, nomeadamente o Pattern ERG (PERG) e os Potências Evocados Visuais (PEV). Através do presente estudo, verificou-se a existência de um atraso acomodativo para todas as visitas efetuadas. As variações ao nível do equivalente esférico (M) e da componente oblíqua do astigmatismo (J45) demonstraram ser estatisticamente significativas. Concluindo desta forma que clinicamente a ortoqueratologia não afeta a resposta acomodativa de baixos míopes. Já a resposta elétrica da retina através Pattern ERG (PERG) demonstrou ao longo do tempo uma melhoria global da resposta das células ganglionares, contudo só apresentou a existência de diferenças estatisticamente significativas ao longo dos dois meses de estudo para o tempo implícito de P50 e N95. Os Potenciais Visuais Evocados (PEV) sofreram alterações mínimas com o tratamento ortoqueratológico e não apresentaram a existência de diferenças estatisticamente significativas. Assim, através deste trabalho podemos concluir que a ortoqueratologia não altera a resposta acomodativa de míopes baixos e também não afeta a resposta elétrica da retina dos mesmos.
In the last few years, several studies have been developed around myopia, based on its progression and associated eye changes. Thus, several techniques have been studied in order to control the progression. Orthokeratology is characterized to be one of the optical procedures that shows systematic effectiveness in controlling the progression of myopia. However, although its effectiveness it is necessary to identify the mechanisms (accommodative, retinal or otherwise) responsible for the effect. The goal of this study was to evaluate through orthokeratology the changes in accommodative function, and also to analyze the change in the response of electrophysiological activity through tests such as Pattern ERG (PERG) and Visual Evoked Potentials. (VEP) over two months. Changes in the following visual parameters were also recorded over two months: refractive error, high and low contrast visual acuity, topographic parameters, light distortion and optical quality. During this period, six visits were made: Pre-appointment, Baseline, 1 Night After, 15 Nights After, 30 Nights After and 60 Nights After orthokeratological treatment. In the pre-appointment, the patient's refractive error and topographic parameters were obtained. In the following visits, all visual parameters were analyzed. Tests such as PERG and VEP were performed on all visits except pre-appointment. For the study, 10 patients (23.20 ± 3.46 years) were recruited with myopia between -1.00 D and -4.00 D, with an astigmatism lower than 1.00 D and with no contraindication to the use of contact lenses. The accommodative response was recorded through the Autorrefratómetro de Campo Aberto WAM-5500 (GrandSeiko Co, Ltd.) coupled to the Badal System, vergence of the stimulus was changed between 0.00 D (infinity), 1.00 D (1 meter), 2.00 D (50 cm), 3.00 D (33 cms), 4.00 D (25 cms) and 5.00 D (20 cms). Electrophysiology measures were also performed, like the Pattern ERG (PERG) and the Visual Evoked Power (VEP). Through the present study, it was verified the existence of an accommodative lag for all visits. The changes in the spherical equivalent (M) and oblique component of astigmatism (J45) proved to be statistically significant. Concluding that corneal orthokeratology does not affect the accommodative response of low myopes. However, the electrical response of the retina through Pattern ERG (PERG) showed over time an overall improvement in the response of ganglion cells, but only showed statistically significant differences over the two-month study for the P50 and N95 peak. Visual Evoked Power (VEP) had minimal changes with orthokeratological treatment and did not show statistically significant differences Thus, through this work we can conclude that the orthokeratology does not affect the accommodative response of low myopes and also doesn`t affect their electrical retinal response.