Academic literature on the topic 'Orthokeratology'

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 &lt 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 &lt 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.

<p>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.</p><p>Aim: The aim of the study was to evaluate how the intraocular pressure, measured with a non-contact tonometer, changes when using orthokeratology lenses.</p><p>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.</p><p>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 ).</p><p>Discussion: This study shows when wearing orthokeratology lenses a decrease in 2, 67 ± 2, 14 mm Hg at day 10 can be expected.</p>

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.