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.

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.

The increasing prevalence of myopia over the past few decades and its association with potential ocular complications make myopia an important research topic. The present work is concerned with the structural and functional characteristics of a group of myopic and emmetropic individuals. The technical experiments in this work investigated firstly the effect of instrument alignment on peripheral refraction measurements and revealed that the corneal vertex was an acceptable alignment position of the Shin-Nippon NVision-K 5001 autorefractor, allowing consistent alignment with other instruments used in this research. Secondly, spectacles could be used to provide comparable vision to contact lenses in the visual performance studies. In the main experimental parts of this work, visual performance and multiple aspects of ocular structure were assessed across a wide range of eccentricities along the horizontal and vertical meridians within the same eyes. The structural properties of the myopic eye were measured through central and peripheral autorefraction, and through cornea to retina dimensions using non-contact biometry. In addition, the central and peripheral resolution acuities of myopic and emmetropic eyes for high and low contrast levels were investigated. Our structural and functional measurements revealed relatively prolate myopic eyes with reduced high contrast resolution acuity, compared to emmetropic eyes. Moreover, multiple regression analyses were performed at the fovea and outermost retinal eccentricities common to all core experiments but revealed no strong relationship between the structure and function of the myopic eye. Finally, regarding asymmetry, the nasal and superior retinae were found to be longer and to perform better in comparison to the temporal and superior retinae respectively.

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.

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

The increasing prevalence of myopia over the past few decades and its association with potential ocular complications make myopia an important research topic. The present work is concerned with the structural and functional characteristics of a group of myopic and emmetropic individuals. The technical experiments in this work investigated firstly the effect of instrument alignment on peripheral refraction measurements and revealed that the corneal vertex was an acceptable alignment position of the Shin-Nippon NVision-K 5001 autorefractor, allowing consistent alignment with other instruments used in this research. Secondly, spectacles could be used to provide comparable vision to contact lenses in the visual performance studies. In the main experimental parts of this work, visual performance and multiple aspects of ocular structure were assessed across a wide range of eccentricities along the horizontal and vertical meridians within the same eyes. The structural properties of the myopic eye were measured through central and peripheral autorefraction, and through cornea to retina dimensions using non-contact biometry. In addition, the central and peripheral resolution acuities of myopic and emmetropic eyes for high and low contrast levels were investigated. Our structural and functional measurements revealed relatively prolate myopic eyes with reduced high contrast resolution acuity, compared to emmetropic eyes. Moreover, multiple regression analyses were performed at the fovea and outermost retinal eccentricities common to all core experiments but revealed no strong relationship between the structure and function of the myopic eye. Finally, regarding asymmetry, the nasal and superior retinae were found to be longer and to perform better in comparison to the temporal and superior retinae respectively.

Yes / Background A recent Genome-wide association meta-analysis (GWAS) of refractive error reported shared genetics with anthropometric traits such as height, BMI and obesity. To explore a potential relationship with refractive error and ocular structure we performed a life-course analysis including both maternal and child characteristics using data from the Avon Longitudinal Study of Parents and Children cohort. Methods Measures collected across the life-course were analysed to explore the association of height, weight, and BMI with refractive error and ocular biometric measures at age 15 years from 1613children. The outcome measures were the mean spherical equivalent (MSE) of refractive error (dioptres), axial length (AXL; mm), and radius of corneal curvature (RCC; mm). Potential confounding variables; maternal age at conception, maternal education level, parental socio-economic status, gestational age, breast-feeding, and gender were adjusted for within each multi-variable model. Results Maternal height was positively associated with teenage AXL (0.010 mm; 95% CI: 0.003, 0.017) and RCC (0.005 mm; 95% CI: 0.003, 0.007), increased maternal weight was positively associated with AXL (0.004 mm; 95% CI: 0.0001, 0.008). Birth length was associated with an increase in teenage AXL (0.067 mm; 95% CI: 0.032, 0.10) and flatter RCC (0.023 mm; 95% CI: 0.013, 0.034) and increasing birth weight was associated with flatter RCC (0.005 mm; 95% CI: 0.0003, 0.009). An increase in teenage height was associated with a lower MSE (− 0.007 D; 95% CI: − 0.013, − 0.001), an increase in AXL (0.021 mm; 95% CI: 0.015, 0.028) and flatter RCC (0.008 mm; 95% CI: 0.006, 0.010). Weight at 15 years was associated with an increase in AXL (0.005 mm; 95% CI: 0.001, 0.009). Conclusions At each life stage (pre-natal, birth, and teenage) height and weight, but not BMI, demonstrate an association with AXL and RCC measured at age 15 years. However, the negative association between refractive error and an increase in height was only present at the teenage life stage. Further research into the growth pattern of ocular structures and the development of refractive error over the life-course is required, particularly at the time of puberty.

The main experimental work of this thesis has been a cross-sectional study of the prevalence of refractive error and its biometric correlates in Middle Eastern adults. In addition dynamic accommodative responses and twenty-four hour axial length fluctuations were investigated in young myopic adults. The prevalence of myopia in 3000 Middle Eastern adults (age range 17-40 years) was similar to previously reported levels of myopia in the West. Myopia was associated with a higher level of education, occupations with a high nearwork demand and positive family history of myopia; all of which have been identified as risk factors for myopia development and progression Diurnal variations in axial length (AL) of similar magnitude to those previously reported in emmetropes were observed in myopes recruited in the current thesis. However, the pattern of the diurnal variation in AL was significantly different between early-onset myopes (EOMs) and late-onset myopes (LOMs). There were no significant differences between EOMs and LOMs in the dynamic accommodative response to a sinusoidally oscillating target. The accommodative phase lag was increased following 30 minute adaptation to myopic defocus using +2.00 D lens. However, intense prolonged (30 minute) nearwork was found to have no effect on accommodative gain or phase lag. A number of recommendations for further work on the prevalence of refractive error in the Middle East are suggested along with further research on diurnal AL variations and dynamic accommodative responses in EOMs and LOMs.

Background: Cross-sectional survey of ocular biometry and visual function in healthy eyes across the life span of a German population aged 20 to 69 years (n = 218). Subject number in percent per age category reflected the percentage within the respective age band of the population of Leipzig, Germany. Methods: Measurements obtained: subjective and objective refraction, best-corrected visual acuity, accommodation, contrast sensitivity, topography and pachymetry with Scheimpflug camera, axial length with non-contact partial coherence interferometry, and spectral-domain optical coherence tomography of the retina. Pearson correlation coefficients with corresponding p-values were given to present interrelationships between stature, biometric and refractive parameters or their associations with age. Two-sample T-tests were used to calculate gender differences. The area under the logarithmic contrast sensitivity function (AULCSF) was calculated for the analysis of contrast sensitivity as a single figure across a range of spatial frequencies. Results: The results of axial length (AL), anterior chamber depth (ACD) and anterior chamber volume (ACV) differed as a function of the age of the participants (rho (p value): AL −0.19 (0.006), ACD −0.56 (< 0.001), ACV-0.52 (< 0.001)). Longer eyes had deeper ACD (AL:ACD 0.62 (< 0.001), greater ACV (AL:ACV 0.65 (< 0.001) and steeper corneal radii (AL:R1ant; R2ant; R1post; R2post 0.40; 0.35; 0.36; 0.36 (all with (< 0.001)). Spherical equivalent was associated with age (towards hyperopia: 0.34 (< 0.001)), AL (−0.66 (< 0.001)), ACD (−0.52 (< 0.001)) and ACV (−0.46 (< 0.001)). Accommodation was found lower for older subjects (negative association with age, r = −0.82 (< 0.001)) and contrast sensitivity presented with smaller values for older ages (AULCSF −0.38, (< 0.001)), no change of retinal thickness with age. 58 % of the study cohort presented with a change of refractive correction above ±0.50 D in one or both eyes (64 % of these were habitual spectacle wearers), need for improvement was present in the young age-group and for older subjects with increasing age. Conclusion: Biometrical data of healthy German eyes, stratified by age, gender and refractive status, enabled cross-comparison of all parameters, providing an important reference database for future patient-based research and specific in-depth investigations of biometric data in epidemiological research. Trial registration: ClinicalTrials.gov # NCT01173614 July 28, 2010

The main experimental work of this thesis has been a cross-sectional study of the prevalence of refractive error and its biometric correlates in Middle Eastern adults. In addition dynamic accommodative responses and twenty-four hour axial length fluctuations were investigated in young myopic adults. The prevalence of myopia in 3000 Middle Eastern adults (age range 17-40 years) was similar to previously reported levels of myopia in the West. Myopia was associated with a higher level of education, occupations with a high nearwork demand and positive family history of myopia; all of which have been identified as risk factors for myopia development and progression Diurnal variations in axial length (AL) of similar magnitude to those previously reported in emmetropes were observed in myopes recruited in the current thesis. However, the pattern of the diurnal variation in AL was significantly different between early-onset myopes (EOMs) and late-onset myopes (LOMs). There were no significant differences between EOMs and LOMs in the dynamic accommodative response to a sinusoidally oscillating target. The accommodative phase lag was increased following 30 minute adaptation to myopic defocus using +2.00 D lens. However, intense prolonged (30 minute) nearwork was found to have no effect on accommodative gain or phase lag. A number of recommendations for further work on the prevalence of refractive error in the Middle East are suggested along with further research on diurnal AL variations and dynamic accommodative responses in EOMs and LOMs.