Arthur Ho

Decrease in Rate of Myopia Progression with a Contact Lens Designed to Reduce Relative Peripheral Hyperopia: One-Year Results

PURPOSE To determine whether a novel optical treatment using contact lenses to reduce relative peripheral hyperopia can slow the rate of progress of myopia. METHODS Chinese children, aged 7 to 14 years, with baseline myopia from sphere -0.75 to -3.50 D and cylinder ≤1.00 D, were fitted with novel contact lenses (n = 45) and followed up for 12 months, and their progress was compared with that of a group (n = 40) matched for age, sex, refractive error, axial length, and parental myopia wearing normal, single-vision, spherocylindrical spectacles. RESULTS On adjusting for parental myopia, sex, age, baseline spherical equivalent (SphE) values, and compliance, the estimated progression in SphE at 12 months was 34% less, at -0.57 D, with the novel contact lenses (95% confidence interval [CI], -0.45 -0.69 D) than at -0.86 D, with spectacle lenses (95% CI, -0.74 to -0.99 D). For an average baseline age of 11.2 years, baseline SphE of -2.10 D, a baseline axial length of 24.6 mm, and 320 days of compliant lens wear, the estimated increase in axial length (AL) was 33% less at 0.27 mm (95% CI, 0.22-0.32 mm) than at 0.40 mm (95% CI, 0.35-0.45 mm) for the contact lens and spectacle lens groups, respectively. CONCLUSIONS The 12-month data support the hypothesis that reducing peripheral hyperopia can alter central refractive development and reduce the rate of progress of myopia. (chictr.org number, chiCTR-TRC-00000029 or chiCTR-TRC-00000032.).

Spectacle lenses designed to reduce progression of myopia: 12-month results.

Purpose. To report the results of 12-month wear of three novel spectacle lens designs intended to reduce peripheral hyperopic defocus and one standard design control lens and their effect on the progression of myopia in Chinese children aged 6 to 16 years. Methods. Chinese children (n = 210) with myopia (−0.75 D to −3.50 D sphere, cylinder ≤−1.50 D) were randomized to one of four groups wearing either one of three novel spectacle lens designs (types I, II, or III) or conventional, single-vision spectacle lenses. Data were collected at 6 and 12 months. Primary and secondary outcome measures were the changes in central cycloplegic auto-refraction and eye axial length, respectively. Peripheral refraction along the horizontal meridian (nasal and temporal) was taken at baseline with and without spectacle lenses. Multivariate linear regression was used to adjust analyses for important covariates. Results. Progression in eyes wearing control spectacle lenses at 6 and 12 months was −0.55 D ± 0.35 D and −0.78 ± 0.50 D, respectively. For the entire group, no statistically significant differences were observed in the rates of progression with the novel designs in comparison to control spectacle lenses. However, in younger children (6 to 12 years) with parental history of myopia (n = 100), there was significantly less progression (−0.68 D ± 0.47 D vs. −0.97 D ± 0.48 D) with lens type III compared with control spectacles (mean difference, 0.29 D, std error, 0.11, p = 0.038). Conclusions. There were no statistically significant differences in the rate of progression of myopia between the control and novel lens wearing eyes for the age group 6 to 16 years. The finding of reduced progression of myopia with type III lens design in younger children with parental myopia needs to be validated in a more targeted study.

Ablation profiles for wavefront-guided correction of myopia and primary spherical aberration

Purpose: To calculate ablation profiles for wavefront‐guided correction of ametropia and primary spherical aberration. Setting: Bascom Palmer Eye Institute, University of Miami, Miami, Florida, USA. Methods: The primary spherical aberrations of the ocular surfaces of an aspheric eye model were calculated before and after simulated ablations for correction of myopia ranging from 0 to 10 diopters. The corneal asphericity to correct primary spherical aberration and the corresponding ablation profiles were also calculated. Results: The corneal asphericity factor that produces zero primary spherical aberration ranges from −0.45 to −0.47. The calculated ablation profiles are parabolic in first approximation, and the ablation depth varies linearly with the amount of correction. To control residual primary spherical aberration with a tolerance of one‐quarter wavelength, the precision of the ablation must range from 0.2 to 0.3 &mgr;m. Conclusions: Ocular aberrometry and corneal topography can be used to calculate ablations for the correction of ametropia and primary spherical aberration. Precise control of postoperative spherical aberration appears to be feasible in theory.

In vitro dimensions and curvatures of human lenses

The purpose of this study was to determine dimensions and curvatures of excised human lenses using the technique of shadowphotogrammetry. A modified optical comparator and digital camera were used to photograph magnified sagittal and coronal lens profiles. Equatorial diameter, anterior and posterior sagittal thickness, anterior and posterior curvatures, and shape factors were obtained from these images. The data were used to calculate lens volumes, which were compared with the lens weights. Measurements were made on 37 human lenses ranging in age from 20 to 99 years. These showed that lens dimensions and the anterior radius of curvature increase linearly throughout adult life while posterior curvature remains constant. The relative shape (or aspect ratio) of the posterior lens is unchanged through adult life since both equatorial diameter and posterior thickness increase at the same rate. The ratio of anterior thickness to posterior thickness is constant at 0.70. It is suggested that in vivo forces alter the apparent location of the lens equator, that the in vitro lens shape corresponds to the maximally accommodated shape in vivo and that the shapes of the accommodated and unaccommodated lens progressively converge toward each other due to lens growth with age, with a convergence point located near the age of total loss of accommodation (55-60 years). Together, these observations provide additional support for the Helmholtz theory of accommodation.

Optimum Dry Eye Classification Using Questionnaire Responses

For the diagnosis of dry eye, global criteria are required that recognize a commonality among all forms of dry eye, even though they do not necessarily identify a particular etiology.1 A dry eye questionnaire2 can serve as a screening instrument with clinic populations and has been shown to be capable of delivering valid sensitivity and specificity information.3 In dry eye research a questionnaire can be used to define treatment groups according to symptoms.4 The feasibility of dry eye related epidemiological surveys of population-based samples may depend on the use of a self-reporting questionnaire.5 Ideally, classification into dry eye and non-dry eye samples is preferred, but a third group with an equivocal diagnosis is usually present for which the terms questionable6 and marginal7 dry eye have been used. The marginal dry eye classification is appropriate for the common presentation of individuals whose tear function is adequate only in favorable conditions and is otherwise deficient in provocative circumstances of air conditioning, central heating, with use of dehydrating medications, following alcohol consumption, and/or with contact lens wear. This investigation is concerned with how dry eye questionnaire responses should be weighted to achieve optimum classification into dry eye, marginal dry eye, and non-dry eye groups.

Optical Power of the Isolated Human Crystalline Lens

PURPOSE To characterize the age dependence of isolated human crystalline lens power and quantify the contributions of the lens surfaces and refractive index gradient. METHODS Experiments were performed on 100 eyes of 73 donors (average 2.8 +/- 1.6 days postmortem) with an age range of 6 to 94 years. Lens power was measured with a modified commercial lensmeter or with an optical system based on the Scheiner principle. The radius of curvature and asphericity of the isolated lens surfaces were measured by shadow photography. For each lens, the contributions of the surfaces and the refractive index gradient to the measured lens power were calculated by using optical ray-tracing software. The age dependency of these refractive powers was assessed. RESULTS The total refractive power and surface refractive power both showed a biphasic age dependency. The total power decreased at a rate of -0.41 D/y between ages 6 and 58.1, and increased at a rate of 0.33D/y between ages 58.1 and 82. The surface contribution decreased at a rate of -0.13 D/y between ages 6 and 55.2 and increased at a rate of 0.04 D/y between ages 55.2 and 94. The relative contribution of the surfaces increased by 0.17% per year. The equivalent refractive index also showed a biphasic age dependency with a decrease at a rate of -3.9 x 10(-4) per year from ages 6 to 60.4 followed by a plateau. CONCLUSIONS The lens power decreases with age, due mainly to a decrease in the contribution of the gradient. The use of a constant equivalent refractive index value to calculate lens power with the lens maker formula will underestimate the power of young lenses and overestimate the power of older lenses.

Imaging and full-length biometry of the eye during accommodation using spectral domain OCT with an optical switch

Abstract: An optical switch was implemented in the reference arm of an extended depth SD-OCT system to sequentially acquire OCT images at different depths into the eye ranging from the cornea to the retina. A custom-made accommodation module was coupled with the delivery of the OCT system to provide controlled step stimuli of accommodation and disaccommodation that preserve ocular alignment. The changes in the lens shape were imaged and ocular distances were dynamically measured during accommodation and disaccommodation. The system is capable of dynamic in vivo imaging of the entire anterior segment and eye-length measurement during accommodation in real-time.

Myopia progression in Chinese children is slower in summer than in winter.

Purpose. To characterize seasonal variation in the myopic progression of Chinese children. Methods. Myopia progression data are presented for a total of 85 Chinese children, aged 6 to 12 years, with baseline myopia of −0.75 D to −3.50 D sphere and astigmatism ⩽−1.50 D, who wore traditional single-vision spectacles in two clinical trials (trial A: n = 37, trial B: n = 48). Refractive error and axial length data were obtained at 6-month intervals using cycloplegic autorefraction and partial coherence interferometry, respectively. Progression rates for right eyes were defined for the first and second 6 months of the studies and classified in terms of “summer,” “autumn,” “winter,” or “spring” based on the mid-point of the 6-month period between visits. Results. The mean 6-month spherical equivalent progression was −0.31 ± 0.25 D for summer, −0.40 ± 0.27 D for autumn, −0.53 ± 0.29 D for winter, and −0.42 ± 0.20 D for spring (p < 0.001). Mean axial elongation was 0.17 ± 0.10 mm for summer, 0.24 ± 0.09 mm for autumn, 0.24 ± 0.09 mm for winter, and 0.15 ± 0.08 mm for spring (p < 0.001). Post hoc analysis indicated that data for summer and winter were different from each other at p < 0.05 for both myopia progression and axial elongation after adjusting for age. Conclusions. Myopia progression in summer months was approximately 60% of that seen in winter, and axial elongation was likewise significantly less in summer. It is unclear whether more time spent outdoors in summer vs. winter is a contributing factor, or the difference in progression rates is a result of “seasonal” variations in the intensity or amount of close work performed. These results indicate that studies of potential myopia treatment strategies should be at least 12 months in duration to take seasonal variations into account.

Influence of accommodation on off-axis refractive errors in myopic eyes

INTRODUCTION This study aims to understand off-axis refraction during accommodation and to identify whether the relative hyperopia generally observed in myopic eyes changes with accommodation. METHOD Twenty bilateral myopes (18 to 33 years) between -0.50 D and -4.25 D (spherical equivalent) and astigmatism less than 1.25 D participated in this study. A soft contact lens was used to correct refractive error for all measurements. Non-cycloplegic autorefraction was measured at the fovea and 20 degrees, 30 degrees, and 40 degrees eccentricities in the nasal and temporal retina at distances of 2 m, 40 cm, and 30 cm. RESULTS Peripheral refractive error, relative to central refraction, became less hyperopic with increasing eccentricity and with increasing accommodation. Lag of accommodation increased with accommodation (p < 0.001) shifting the image-shell backward relative to the retina. In the farther periphery, there was either no change in refractive error or increased myopic shifts with accommodation. Astigmatism increased with eccentricity and significantly increased in the farther eccentricities with accommodation (p < 0.001). CONCLUSION Myopes display hyperopic shifts in the center and near peripheral field during near-viewing, while the farther periphery either remains unshifted or demonstrates a myopic shift. These results are due to the combined effect of lag of accommodation and an increased curvature of field during accommodation.

Myopia Progression Rates in Urban Children Wearing Single-Vision Spectacles

Purpose. To conduct a meta-analysis on the rates of myopia progression in urban children of Asian and predominately European ethnicities who are corrected with traditional single-vision spectacles. Methods. A search of the National Library of Medicines PubMed literature database for articles on myopia progression was conducted using the terms “myopi*progression” and MeSH terms “myopia” and “disease progression,” and limited to publications from January 1990 and only for articles reporting data for humans <16 years of age. Studies were excluded if they were non-randomized, did not use cycloplegic autorefraction, had a sample size <30 individuals, examined high myopia (worse than −6.0 D) or special subject groups, presented myopia as part of a syndrome or condition, were retrospective, or used controls wearing optical corrections other than spectacles. Results. Of 175 articles identified, 20 remained after applying the exclusion criteria. The estimated myopia progression at a mean age of 9.3 years after 1 year of follow-up was −0.55 D [95% confidence interval (CI), −0.39 to −0.72 D] for populations of predominantly European extraction and −0.82 D (95% CI, −0.71 to −0.93 D) for Asians. The estimated progression rates were dependent on baseline age, with decreasing progression as age increased. The rates also varied with gender. For an average baseline age of 8.8 years, estimated annual progression (combined ethnicities) was −0.80 D/yr for females (95% CI, −0.51 to −1.10), and a significantly slower (p < 0.01) −0.71 D/yr for males (95% CI, −0.42 to −1.00). Conclusions. In children wearing single-vision spectacles, higher myopia progression rates were found in urban Asians compared with urban populations of predominantly European descent. Younger children and females demonstrated greater annual rates of progression of myopia.