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.

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.

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.

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.

D.Phil. (Optometry) / Please refer to full text to view abstract

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.

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.

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.

No description available.

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.