Experimental animal myopia models are applicable to human juvenile-onset myopia

Diurnal retinal and choroidal gene expression patterns support a role for circadian biology in myopia pathogenesis

The prevalence of myopia (nearsightedness) is increasing to alarming levels, but its etiology remains poorly understood. Because both laboratory and clinical findings suggest an etiologic role for circadian rhythms in myopia development, we assayed gene expression by RNA-Seq in retina and choroid at the onset of unilateral experimental myopia in chick, isolating tissues every 4 h during a single 24-h period from myopic and contralateral control eyes. Occluded versus open eye gene expression differences varied considerably over the 24-h sampling period, with some occurring at multiple times of day but with others showing differences at only a single investigated timepoint. Some of the genes identified in retina or choroid of chick myopia were previously identified as candidate genes for common human myopia. Like differentially expressed genes, pathways identified by Gene Set Enrichment Analysis also varied dramatically by sampling time. Considered with other laboratory data, human genetic and epidemiology data, these findings further implicate circadian events in myopia pathogenesis. The present results emphasize a need to include time of day in mechanistic studies of myopia and to assess circadian biology directly in trying to understand better the origin of myopia and to develop more effective therapies.

Clinical and Genetic Landscape of Ectopia Lentis Based on a Cohort of Patients From 156 Families

Purpose

To extend the mutation spectrum and explore the characteristics of genotypes and ocular phenotypes in ectopia lentis (EL).

Methods

Variants in all 14 reported EL-associated genes were selected from in-house data sets as well as literature review, and available clinical data were analyzed.

Results

Likely pathogenic variants in three genes were identified in 156 unrelated families with EL from the in-house cohort, of which 97.4% resulted from variants in FBN1, whereas the remaining were caused by variants in ADAMTSL4 (1.3%) and LTBP2 (1.3%). A comparative analysis of the in-house data and literature review suggested several characteristics: (1) a higher proportion of cysteine involvement variants in FBN1, either variants introducing or eliminating cysteine, and an earlier diagnosis age were presented in our cohort than in published literature; (2) the axial length (AL) and refractive error increased more rapidly with age in preschool EL children than normal children, and the increased rate of AL was slower in patients with surgery than those without surgery; (3) aberrant astigmatism was common in EL; and (4) worse vision and earlier onset age were observed in patients with non-FBN1 variants (all P < 0.05).

Conclusions

Variants in FBN1 are the predominant cause of EL, with the most common cysteine involvement variants. Early-stage EL manifests refractive error but gradually converts to axial myopia through defocus introduced by lens dislocation. Aberrant astigmatism is a suggestive sign of EL. Non-FBN1 variants cause early-onset and severe phenotypes. These results provide evidence for early diagnosis as well as timely treatment for EL.

Optical biometry and influence of media opacity due to cataract on development of axial length in NorthEast Indian paediatric patients- A prospective study

AIM

To study the influence of media opacity due to cataract on the development of axial length in paediatric patients from North-East India, using optical biometry.

METHOD

This is a prospective, observational study, including consecutive patients attending the paediatric ophthalmology clinic, over a period of 1 year. Patients with other ocular and systemic diseases, unfit for optical biometry measurements due to dense cataract, nystagmus and strabismus were excluded and rest divided into three groups after proper age matching - 1. Group A (Bilateral cataract) 2. Group B (Unilateral cataract) 3. Group C (Bilateral normal). The axial length of the various groups was analysed using independent sample test (for bilateral cataract group) and paired t-test (for unilateral cataract group). Linear regression analysis between age and axial length was done.

RESULTS

A total of 177 patients were included.80 cases in Group A (bilateral cataract), 18 cases in Group B (unilateral cataract) and 79 in Group C (bilateral normal) The mean age of the patients in all the groups was 8.88 ± 3.51 years (range: 1-17 years). The bivariate analysis and simple linear regression revealed a statistically significant correlation between age and AL in case of cataractous eyes. (Pearson's coefficient: 0.341, p < 0.001). The mean AL was significantly longer (p = 0.013) in the cataractous eyes (mean = 23.38 ± 2.08 mm) of Group A(bilateral cataract) in the 7-12 years age group as compared to the bilaterally normal eyes (mean AL = 22.57 ± 0.70 mm) of patients in the same age group in Group C. The mean AL of cataractous eyes in group B (unilateral cataract) (mean = 22.46 ± 1.73 mm) as compared to the fellow normal eyes, (mean = 21.87 ± 0.97 mm) was not statistically significant.

CONCLUSION

Cataractous eyes have an abnormal axial length development. The influence of media opacity due to cataract on development of axial length in paediatric eyes in the North-East Indian population is variable, in line with global data on the same. Although there is some influence of media opacity, the exact nature is not clearly understood and may have a crucial interaction with genetic and other environmental factors. Genetic testing integrated with biometric analysis is recommended for further understanding of the ocular growth and development.

The Willingness of Patients to Participate in an Eye Donation Registry for Research

INTRODUCTION

For ophthalmologic research, the systematic correlation of clinical data with data obtained from postmortem tissue donation is of great benefit. In this respect, the establishment of an eye donation registry represents a prerequisite for the acquisition of such data.

METHODS

A total of 300 patients were interviewed at a tertiary referral center in Germany by means of a standardized questionnaire. Binary questions were evaluated by percentage; Likert-scaled questions (1 = does apply; 5 = does not apply) were analyzed by the median and 25th (Q25) and 75th (Q75) percentiles.

RESULTS

The majority of patients (77.0%) would agree to donate their eyes for research purposes. When asked about reasons against an eye donation, 60.9% of all patients only stated reasons in the category "addressable" (e.g., not enough awareness of the topic). The vast majority of patients considered it appropriate for an ophthalmologist to approach them on the issue of postmortem eye donation (median 1, Q25 1, Q75 1).

CONCLUSION

Overall, patients had a positive attitude towards postmortem eye donation for research purposes. Importantly, reasons given against postmortem eye donation were often related to misconceptions and were potentially addressable. These results underline the fundamental willingness of ophthalmological patients in Germany to donate their eyes postmortem for research purposes.

The relationship between image degradation and myopia in the mammalian eye

BACKGROUND

In all species studied, myopia develops if the eye is deprived of detailed vision during development (form deprivation myopia). However, different degrees of spatial image deprivation produce different effects and have not been described in the mammalian eye. Therefore, the effect of image degradation on guinea pig emmetropisation was investigated.

METHODS

Eighty-one guinea pigs wore a treatment on one eye from 6 to 13 days of age. There were four treatments: a translucent diffuser (no lines or edges were visible through the diffuser); one of five Bangerter foils (BF: 0.8, 0.6, 0.4, 0.2, light perception only), which differed in their cut-off spatial frequencies; a 'ring mount' control with no filter; or one of two neutral density filters that reduced luminance only (ND, optical density grades 0.1 and 0.6). Refractive error and ocular elongation were measured after seven days of treatment.

RESULTS

The extent of induced myopia and ocular growth were related to the amount of image degradation (mean difference between the treated and untreated eyes changed in a graded manner -7.0 D to -0.2 D and from 85 µm to seven µm respectively, for spatial frequency cut-offs between zero and 24 cycles per degree). Corresponding reductions in luminance from ND filters did not increase eye growth and caused significantly less myopia than the BFs that caused a similar luminance decrement. The greatest myopia occurred when no or limited spatial information was available to the eye, but moderate myopia still occurred with spatial frequency cut-offs of six and 12 cycles per degree, well beyond the visual acuity range of guinea pigs.

CONCLUSION

Excessive ocular growth and myopia are most robust when induced by spatial frequency reductions within the visual acuity range but can also be induced beyond this. Either the mechanism of ocular growth can detect supra-threshold spatial frequencies, possibly due to aliasing, or it is sensitive to small amounts of contrast degradation.

The progression of corrected myopia

PURPOSE

This study seeks to demonstrate the existence of a feedback loop controlling myopia by comparing the prediction of a feedback model to the actual progression of corrected myopia. In addition to theoretical results, confirming clinical data are presented.

METHODS

The refraction of 13 continuously corrected myopic eyes was collected over a period of time ranging from 4 to 9 years from the time of their first correction. Refractive data was collected in an optometry office from myopic young subjects from the general population in Boston. Subjects were myopes, ages 2 to 22 at the time of first correction selected randomly from a larger population. All individuals were fully corrected with lenses; new lenses were prescribed every time that their myopia increased by 0.25 diopters or more. Subjects wore their spectacle lenses during the followed period.

RESULTS

Subjects exhibit a linear time course of myopia progression when corrected with lenses. The observed rate of myopia increase is 0.2 to 1.0 diopters/year, with a mean correlation coefficient r  = -0.971, p < 0.005.

CONCLUSIONS

This report establishes that feedback control theory applies to the clinical phenomenon of progressive myopia. Continuous correction of myopia results in a linear progression that increases myopia. The Laplace transformation of temporal refractive data to the s-domain simplifies the study of myopia and emmetropia. The feedback transfer function predicts that continuous correction of myopia results in a linear progression because continuous correction opens the feedback loop. This prediction is confirmed with all subjects.

Human parallels to experimental myopia? A literature review on visual deprivation

Raviola and Wiesel's monkey eyelid suture studies of the 1970s laid the cornerstone for the experimental myopia science undertaken since then. The aim has been to clarify the basic humoral and neuronal mechanisms behind induced myopization, its eye tissue transmitters in particular. Besides acquiring new and basic knowledge, the practical object of the research is to reduce the burden of human myopia around the world. Acquisition and cost of optical correction is one issue, but associated morbidity counts more, with its global load of myopia-associated visual loss and blindness. The object of the present PubMed literature-based review is to evaluate apparent similarities between experience from disturbed imaging in experimental laboratory science and varieties within the spectrum of childhood human myopia. So far, the main impression is that macroscopical optical deprivation appears absent in the prevalent types of human myopia, nor is myopia a regular sequel where early eye pathology has led to poor imaging and optical deprivation. Optical aberrations of a higher order are a relatively new issue in myopia research, and microstructural deprivation is only marginally dealt within the survey. Links between experimental and human myopia appear mainly occasional, and with only few examples in humans where factual parallels appear credible. Clinical and epidemiological data on refraction remain important, in particular with a view to life style and environmental factors. Such knowledge may further serve as inspiration to the laboratory research, which aims at solving the basic enigmas on a tissue level.

Rapid, accurate, and non-invasive measurement of zebrafish axial length and other eye dimensions using SD-OCT allows longitudinal analysis of myopia and emmetropization

Refractive errors in vision can be caused by aberrant axial length of the eye, irregular corneal shape, or lens abnormalities. Causes of eye length overgrowth include multiple genetic loci, and visual parameters. We evaluate zebrafish as a potential animal model for studies of the genetic, cellular, and signaling basis of emmetropization and myopia. Axial length and other eye dimensions of zebrafish were measured using spectral domain-optical coherence tomography (SD-OCT). We used ocular lens and body metrics to normalize and compare eye size and relative refractive error (difference between observed retinal radial length and controls) in wild-type and lrp2 zebrafish. Zebrafish were dark-reared to assess effects of visual deprivation on eye size. Two relative measurements, ocular axial length to body length and axial length to lens diameter, were found to accurately normalize comparisons of eye sizes between different sized fish (R2=0.9548, R2=0.9921). Ray-traced focal lengths of wild-type zebrafish lenses were equal to their retinal radii, while lrp2 eyes had longer retinal radii than focal lengths. Both genetic mutation (lrp2) and environmental manipulation (dark-rearing) caused elongated eye axes. lrp2 mutants had relative refractive errors of -0.327 compared to wild-types, and dark-reared wild-type fish had relative refractive errors of -0.132 compared to light-reared siblings. Therefore, zebrafish eye anatomy (axial length, lens radius, retinal radius) can be rapidly and accurately measured by SD-OCT, facilitating longitudinal studies of regulated eye growth and emmetropization. Specifically, genes homologous to human myopia candidates may be modified, inactivated or overexpressed in zebrafish, and myopia-sensitizing conditions used to probe gene-environment interactions. Our studies provide foundation for such investigations into genetic contributions that control eye size and impact refractive errors.

Is myopia a failure of homeostasis?

This review examines the hypothesis that human myopia is primarily a failure of homeostasis (i.e. regulated growth) and also considers the implications this has for research into refractive errors. There is ample evidence for homeostatic mechanisms in early life. During the first few years of life the eye grows toward emmetropia, a process called emmetropization. The key statistical features of this process are a shift of the mean population refraction toward emmetropia and a reduction in variability. Refractive errors result when either this process fails (primary homeostatic failure) or when an eye that becomes emmetropic fails to remain so during subsequent years (secondary homeostatic failure). A failure of homeostasis should increase variability as well as causing a possible shift in mean refraction. Increased variability is indeed seen in both animal models of myopia such as form deprivation and in human populations from the age of 5 or 6 onwards. Considering ametropia as a homeostatic failure also fits with the growing body of evidence that a wide range of factors and events can influence eye growth and refraction from gestation, through infancy, childhood and into adulthood. It is very important to recognize that the refraction of an eye is not a simple trait like eye colour but the consequence of the complex process of eye growth throughout life. To understand how an eye ends up with a specific refraction it is essential to understand all the factors that may promote the attainment and maintenance of emmetropia. Equally important are the factors that may either disrupt early emmetropization or lead to a loss of emmetropia during later development. Therefore, perhaps the most important single implication of a homeostatic view of myopia is that this condition is likely to have a very wide range of causes. This may allow us to identify subgroups of myopia for which specific environmental influences, genes or treatments can be found, effects that might be lost if all myopes are considered to be equivalent.

Pharmacology of myopia and potential role for intrinsic retinal circadian rhythms

Despite the high prevalence and public health impact of refractive errors, the mechanisms responsible for ametropias are poorly understood. Much evidence now supports the concept that the retina is central to the mechanism(s) regulating emmetropization and underlying refractive errors. Using a variety of pharmacologic methods and well-defined experimental eye growth models in laboratory animals, many retinal neurotransmitters and neuromodulators have been implicated in this process. Nonetheless, an accepted framework for understanding the molecular and/or cellular pathways that govern postnatal eye development is lacking. Here, we review two extensively studied signaling pathways whose general roles in refractive development are supported by both experimental and clinical data: acetylcholine signaling through muscarinic and/or nicotinic acetylcholine receptors and retinal dopamine pharmacology. The muscarinic acetylcholine receptor antagonist atropine was first studied as an anti-myopia drug some two centuries ago, and much subsequent work has continued to connect muscarinic receptors to eye growth regulation. Recent research implicates a potential role of nicotinic acetylcholine receptors; and the refractive effects in population surveys of passive exposure to cigarette smoke, of which nicotine is a constituent, support clinical relevance. Reviewed here, many puzzling results inhibit formulating a mechanistic framework that explains acetylcholine's role in refractive development. How cholinergic receptor mechanisms might be used to develop acceptable approaches to normalize refractive development remains a challenge. Retinal dopamine signaling not only has a putative role in refractive development, its upregulation by light comprises an important component of the retinal clock network and contributes to the regulation of retinal circadian physiology. During postnatal development, the ocular dimensions undergo circadian and/or diurnal fluctuations in magnitude; these rhythms shift in eyes developing experimental ametropia. Long-standing clinical ideas about myopia in particular have postulated a role for ambient lighting, although molecular or cellular mechanisms for these speculations have remained obscure. Experimental myopia induced by the wearing of a concave spectacle lens alters the retinal expression of a significant proportion of intrinsic circadian clock genes, as well as genes encoding a melatonin receptor and the photopigment melanopsin. Together this evidence suggests a hypothesis that the retinal clock and intrinsic retinal circadian rhythms may be fundamental to the mechanism(s) regulating refractive development, and that disruptions in circadian signals may produce refractive errors. Here we review the potential role of biological rhythms in refractive development. While much future research is needed, this hypothesis could unify many of the disparate clinical and laboratory observations addressing the pathogenesis of refractive errors.

Time outdoors and physical activity as predictors of incident myopia in childhood: a prospective cohort study

PURPOSE

Time spent in "sports/outdoor activity" has shown a negative association with incident myopia during childhood. We investigated the association of incident myopia with time spent outdoors and physical activity separately.

METHODS

Participants in the Avon Longitudinal Study of Parents and Children (ALSPAC) were assessed by noncycloplegic autorefraction at ages 7, 10, 11, 12, and 15 years, and classified as myopic (≤-1 diopters) or as emmetropic/hyperopic (≥-0.25 diopters) at each visit (N = 4,837-7,747). Physical activity at age 11 years was measured objectively using an accelerometer, worn for 1 week. Time spent outdoors was assessed via a parental questionnaire administered when children were aged 8-9 years. Variables associated with incident myopia were examined using Cox regression.

RESULTS

In analyses using all available data, both time spent outdoors and physical activity were associated with incident myopia, with time outdoors having the larger effect. The results were similar for analyses restricted to children classified as either nonmyopic or emmetropic/hyperopic at age 11 years. Thus, for children nonmyopic at age 11, the hazard ratio (95% confidence interval, CI) for incident myopia was 0.66 (0.47-0.93) for a high versus low amount of time spent outdoors, and 0.87 (0.76-0.99) per unit standard deviation above average increase in moderate/vigorous physical activity.

CONCLUSION

Time spent outdoors was predictive of incident myopia independently of physical activity level. The greater association observed for time outdoors suggests that the previously reported link between "sports/outdoor activity" and incident myopia is due mainly to its capture of information relating to time outdoors rather than physical activity.

Perspective: how might emmetropization and genetic factors produce myopia in normal eyes?

Substantial evidence has emerged over the past decades for a role of genetics in the development of human refractive error. There is also an emmetropization mechanism that uses visual signals to match the axial length to the focal plane. There has been little discussion of how these two important factors might interact. We explore here ways in which genetic factors driving axial growth may interact with the emmetropization mechanism, mostly to produce emmetropic eyes but often to produce myopia. An important factor may be a normal, yet reduced ability of juvenile eyes to use myopia to restrain genetically driven axial elongation. Reduced ability to respond to myopia by slowing axial elongation may contribute to the development of myopia in cases where genetics alone would make the axial length longer than the focal plane.

Effects of confined space and near vision stimulation on refractive status and vitreous chamber depth in adolescent rhesus monkeys

This study aimed to investigate the effects of sustained near vision stimulation, on the refractive development and elongation of the vitreous chamber in adolescent rhesus monkeys. A total of 12 adolescent rhesus monkeys (1.5-2.0 years old) were randomly assigned to 3 groups. In groups A (n=4) and B (n=4), monkeys were reared in close-vision cages for 8 and 4 h d(-1), respectively; tiny granules were added on the cage floor to avoid visual deprivation and to encourage near gaze. In group C (n=4), monkeys were reared in open-vision cages, with non-granule food as a control. Vitreous chamber depth, refractive status, and corneal refractive power were assessed over 18 months. Paired t-test was used to compare the differences and a P-value<0.05 was considered to be statistically significant. In group A, vitreous chamber depth and optical axis elongated significantly, and refractive error shifted towards myopia during the observation period. In group B, vitreous chambers and optical axis elongated but the refractive power did not show significant changes. In group C, there was no significant elongation in vitreous chambers and optical axis, and the refractive power changed slightly towards hypermetropia. There were no significant changes in corneal refractive power in each group. Sustained near vision can promote vitreous chamber growth and induce myopic shifts in refractive power in adolescent monkeys. Our results demonstrate the potential for a primate model of near-work-related myopia.

Nature and nurture: the complex genetics of myopia and refractive error

The refractive errors, myopia and hyperopia, are optical defects of the visual system that can cause blurred vision. Uncorrected refractive errors are the most common causes of visual impairment worldwide. It is estimated that 2.5 billion people will be affected by myopia alone within the next decade. Experimental, epidemiological and clinical research has shown that refractive development is influenced by both environmental and genetic factors. Animal models have showed that eye growth and refractive maturation during infancy are tightly regulated by visually guided mechanisms. Observational data in human populations provide compelling evidence that environmental influences and individual behavioral factors play crucial roles in myopia susceptibility. Nevertheless, the majority of the variance of refractive error within populations is thought to be because of hereditary factors. Genetic linkage studies have mapped two dozen loci, while association studies have implicated more than 25 different genes in refractive variation. Many of these genes are involved in common biological pathways known to mediate extracellular matrix (ECM) composition and regulate connective tissue remodeling. Other associated genomic regions suggest novel mechanisms in the etiology of human myopia, such as mitochondrial-mediated cell death or photoreceptor-mediated visual signal transmission. Taken together, observational and experimental studies have revealed the complex nature of human refractive variation, which likely involves variants in several genes and functional pathways. Multiway interactions between genes and/or environmental factors may also be important in determining individual risks of myopia, and may help explain the complex pattern of refractive error in human populations.

The effect of age on compensation for a negative lens and recovery from lens-induced myopia in tree shrews (Tupaia glis belangeri)

We examined in tree shrews the effect of age on the development of, and recovery from, myopia induced with a negative lens. Starting at 11, 16, 24, 35 or 48days after natural eye-opening (days of visual experience [VE]), juvenile tree shrews (n=5 per group) wore a monocular -5D lens for 11days. A long-term lens-wear group (n=6) began treatment at 16days of VE and wore the lens for 30days. A young adult group (n=5) began to wear a -5D lens between 93 and 107days of VE (mean+/-SD, 100+/-6days of VE) and wore the lens for 29-54days (mean+/-SD, 41.8+/-9.8days). The recovery phase in all groups was started by discontinuing -5D lens wear. Contralateral control eyes in the three youngest groups were compared with a group of age-matched normal eyes and showed a small (<1D), transient myopic shift. The amount of myopia that developed during lens wear was measured as the difference between the treated and control eye refractions. After 11days of lens wear, the induced myopia was similar for the four younger groups (near full compensation: 11days, -5.1+/-0.4D; 16days, -4.7+/-0.3D; 24days, -4.9+/-0.4D; 35days, -4.0+/-0.02) and slightly less in the oldest juvenile group (48days, -3.3+/-0.5D). The young adult animals developed -4.8+/-0.3D of myopia after a longer lens-wear period. The rate of compensation (D/day) was high in the 4 youngest groups and decreased in the 48-day and young adult groups. The refractions of the long-term lens-wear juvenile group remained stable after compensating for the -5D lens. During recovery, all animals in the youngest group recovered fully (<1D residual myopia) within 7days. Examples of both rapid (<10days) and slow recovery (>12days) occurred in all age groups except the youngest. Every animal showed more rapid recovery (higher recovery slope) in the first 4days than afterward. One animal showed extremely slow recovery. Based on the time-course of myopia development observed in the youngest age groups, the start of the susceptible period for negative-lens wear is around 11-15days after eye opening; the rate of compensation remains high until approximately 35days of VE and then gradually declines. Compensation is stable with continued lens wear. The emmetropization mechanism, both for lens compensation and recovery, remains active into young adulthood. The time-course of recovery is more variable than that of compensation and seems to vary with age, with the amount of myopia (weakly) and with the individual animal.

Axial Length: A Risk Factor for Cataractogenesis

Introduction: To evaluate whether eyes with longer axial lengths are associated more often with clinically significant cataracts than eyes with shorter axial lengths. Materials and Methods: Charts of consecutive patients who underwent cataract surgery by 4 resident surgeons at Los Angeles County Hospital from July 2001 through May 2002 were retrospectively reviewed. Those patients whose axial lengths were significantly different between the 2 eyes (≥0.30 mm) and who had no pathology (other than cataracts) affecting visual acuity were included in the study. The 2 eyes in each patient were compared for preoperative best-corrected visual acuity and severity of cataracts. Results: Thirty-four of 353 patients had interocular axial length differences of at least 0.3 mm and were included in this study. Thirty-one patients had worse, 1 had equal, and 2 had better preoperative vision in the eye with longer versus the shorter axial length. Fourteen patients had more severe, 11 had the same, and 1 had less severe posterior subcapsular cataract (PSC) in the eye with longer axial length. In 8 patients, PSC severity could not be assessed due to obscuring nuclear sclerosis. Twenty-four patients had more severe, 7 patients had equal, and 3 patients had less severe nuclear sclerosis in the longer eye. Overall, longer axial lengths correlated with worse visual acuity, posterior subcapsular cataracts, and nuclear sclerosis. Diabetic status did not affect the correlation. The correlations were stronger with greater axial length asymmetry. Conclusions: Eyes with longer axial lengths have a higher prevalence of cataracts. Key words: Axial myopia, Cataract formation

Form-deprivation myopia in the guinea pig (Cavia porcellus)

Form deprivation (FD) was induced in 61 guinea pigs with a diffuser worn on one eye. The form-deprived eye elongated and developed myopia within 6 days in animals raised under a 12:12 h light/dark cycle, but not when reared in darkness. After 11 days of FD, the average eye was -6.6 D more myopic and 146 microm longer than its fellow eye. Initially the myopia was mostly from vitreous chamber elongation, but with longer periods of FD, corneal power increases predominated. These effects were confirmed in schematic eyes. After a delay, FD also elongated the vitreous chamber of the non-deprived eye. The myopia rapidly abated once the diffusers were removed (65% within 24 h) due to inhibition of elongation and choroidal thickening. The guinea pig provides a fast mammalian model of FD myopia and corneal curvature regulation.

Anisometropia in Singapore school children

PURPOSE

To report the prevalence rates of anisometropia in a school population and determine the relative contribution of refractive power and axial length to the measured anisometropia.

DESIGN

Population-based cross-sectional study.

METHODS

Autorefraction, keratometry, and ultrasonography studies were made.

SETTING

Three schools, located on the eastern, northern, and western part of Singapore.

STUDY POPULATION

In all, 1,979 children aged 7 to 9 years were recruited for this study. The study sample included Chinese (n = 1,481), Malay (n = 324), and Asian Indian (n = 174) children; 720 subjects have myopia (spherical equivalent <= -0.5 diopters) in at least one eye.

MAIN OUTCOME MEASURE

Anisometropia.

RESULTS

The prevalence rates of anisometropia, in terms of spherical equivalent (SE) difference of at least 1.5 diopters and 2.0 diopters were 1.57% (95% confidence interval [CI]: 1.1, 2.2) and 1.01% (95% CI: 0.6, 1.6), respectively. The prevalence rate of anisometropia (at least 2.0 diopters) among the children with at least one myopic eye was 2.4% (95% CI: 1.4, 3.8), whereas in those without any myopic eyes, the prevalence rate was only 0.2% (95% CI: 0.06, 0.8). The spherical equivalent difference between the right and left eyes was positively correlated with the difference in axial lengths (P <.001). The difference in corneal refractive power is not statistically different between the anisometropic and the nonanisometropic children.

CONCLUSIONS

The anisometropia prevalence rate in a childhood population with a relatively high prevalence of myopia was reported. The origin of the anisometropia is axial, and these results suggest that the differential rate of elongation between the two eyes of nonmyopic subjects results in anisometropia.

Hyperinsulinemic diseases of civilization: more than just Syndrome X

Compensatory hyperinsulinemia stemming from peripheral insulin resistance is a well-recognized metabolic disturbance that is at the root cause of diseases and maladies of Syndrome X (hypertension, type 2 diabetes, dyslipidemia, coronary artery disease, obesity, abnormal glucose tolerance). Abnormalities of fibrinolysis and hyperuricemia also appear to be members of the cluster of illnesses comprising Syndrome X. Insulin is a well-established growth-promoting hormone, and recent evidence indicates that hyperinsulinemia causes a shift in a number of endocrine pathways that may favor unregulated tissue growth leading to additional illnesses. Specifically, hyperinsulinemia elevates serum concentrations of free insulin-like growth factor-1 (IGF-1) and androgens, while simultaneously reducing insulin-like growth factor-binding protein 3 (IGFBP-3) and sex hormone-binding globulin (SHBG). Since IGFBP-3 is a ligand for the nuclear retinoid X receptor alpha, insulin-mediated reductions in IGFBP-3 may also influence transcription of anti-proliferative genes normally activated by the body's endogenous retinoids. These endocrine shifts alter cellular proliferation and growth in a variety of tissues, the clinical course of which may promote acne, early menarche, certain epithelial cell carcinomas, increased stature, myopia, cutaneous papillomas (skin tags), acanthosis nigricans, polycystic ovary syndrome (PCOS) and male vertex balding. Consequently, these illnesses and conditions may, in part, have hyperinsulinemia at their root cause and therefore should be classified among the diseases of Syndrome X.

Progressive axial myopia in a juvenile patient with traumatic glaucoma

PURPOSE

To report a case of progressive axial myopia associated with traumatic glaucoma in a juvenile patient with no systemic disease.

DESIGN

Interventional case report.

METHODS

In a 15-year-old male, serial ocular examinations, including manifest refraction, tonometry, and axial eye length measurement, were performed over a 6-year period, beginning with blunt trauma, right eye, followed by a series of surgical procedures for traumatic cataract and glaucoma.

RESULTS

A 4-diopter myopic shift (from -1.25 to -5.25) with a 1.5 mm increase in the axial eye length occurred, whereas the intraocular pressure increased from 21 to 46 mm Hg, during a 2-year period. The refraction, axial eye length, and intraocular pressure remained stable during the same period in the fellow, normal eye.

CONCLUSION

Progressive axial myopia associated with traumatic glaucoma is possible in a juvenile patient in his late teens.

Distribution of refractive errors in albinos and persons with idiopathic congenital nystagmus

We compared retrospectively the distribution of refractive errors in a sample of adolescent and adult albinos (n = 19) with that in persons with idiopathic congenital nystagmus (CN) (n = 46), whose eye movements are similar to those of albinos but whose visual acuity is better. The distribution of spherical-equivalent refractive errors is more broadly distributed and slightly less myopic in albinos than in persons with idiopathic CN. On average, albinos also have more astigmatism (primarily with-the-rule), than persons with idiopathic CN. Unlike the leptokurtic distribution of refractive error that characterizes the normal adolescent and adult population, the distributions of refractive error for albinos and for persons with idiopathic CN exhibit no significant kurtosis. Moreover, neither group of subjects exhibits significant kurtosis for refractive errors in the vertical meridian, which corresponds to the retinal-image orientation with the least motion smear during horizontal nystagmus. The absence of significant leptokurtosis in the refractive-error distributions of young-adult albinos and persons with idiopathic CN suggests that the presence of nystagmus may interfere with normal refractive development.

An evolutionary analysis of the aetiology and pathogenesis of juvenile-onset myopia

The available evidence suggests that both genes and environment play a crucial role in the development of juvenile-onset myopia. When the human visual system is examined from an evolutionary perspective, it becomes apparent that humans, living in the original environmental niche for which our species is genetically adapted (as hunter-gatherers), are either slightly hypermetropic or emmetropic and rarely develop myopia. Myopia occurs when novel environmental conditions associated with modern civilization are introduced into the hunter-gatherer lifestyle. The excessive near work of reading is most frequently cited as the main environmental stressor underlying the development of myopia. In this review we point out how a previously unrecognized diet-related malady (chronic hyperinsulinaemia) may play a key role in the pathogenesis of juvenile-onset myopia because of its interaction with hormonal regulation of vitreal chamber growth.

Refraction in juvenile chronic arthritis: a long-term follow-up study, with emphasis on myopia

OBJECTIVE

Assessment of refraction anomalies in juvenile chronic arthritis (JCA) on a long-term follow-up basis.

MATERIAL AND METHODS

Sixty-five adults, 52 females and 13 males, with a history of active JCA had a complete ophthalmic evaluation including subjective refractioning on average 26.4 years after JCA onset. The age range was 22-49 years.

RESULTS

The refraction ranged from -8.12 D to +6.5 D with a mean (SD) of -0.64 (2.16) D. The mean refraction in the JCA group was significantly more towards myopia than that of a coeval adult hospital-based sample used as controls (p = 0.008). Twenty-eight out of the 65 (43%) had a negative refractive value of at least 0.37 D. Myopia onset age ranged from 8 to 31 years. In those able to specify their myopia onset by first purchase of spectacles (n = 25) the JCA onset had preceded the myopia, with a mean (SD) interval of 10.1 (5.4) years.

CONCLUSION

The elevated myopia figure of 43% among JCA patients suggests an association between myopia and JCA. In lack of more precise indicators and in accordance with older literature, an explanation might be a weakening effect of chronic inflammation on scleral connective tissue.