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PubMed2005

Methods for a population-based study of myopia and other eye conditions in school children: the Sydney Myopia Study.

PURPOSE: The Sydney Myopia Study will establish the prevalence of myopia and other eye diseases in a large representative sample of Sydney school children. It will also examine the relationship between myopia and potential modifiable risk factors and will assess potential gene-environment interactions by examining parents and siblings. METHODS: The target population is a stratified random cluster sample of 1750 Year 1 (age 6 years) and 1500 Year 7 (age 12 years) students from Sydney metropolitan schools. Procedures (comprehensive parent-administered questionnaire and examination) involve standardized protocols to allow for comparison with international population-based data. Examinations include a detailed assessment of visual acuity, cover testing for strabismus, identification of amblyopia, slit-lamp examination, non-contact ocular biometry and cycloplegia (cyclopentolate) followed by autorefraction, optical coherence tomography, retinal thickness measurement, digital mydriatic retinal photography and aberrometry. CONCLUSIONS: The Sydney Myopia Study design and methodology will ensure valid findings on ocular development and health in a large representative sample of Sydney school children, for comparison with other population-based refraction data.

Adolescent↗
PubMedDate not supplied

Correction of high myopia with the Worst myopia claw intraocular lens.

BACKGROUND: Phakic anterior chamber lenses is one of the modalities used to correct high myopia. We report the initial results of our prospective study on the Worst myopia claw intraocular lens (IOL) that is fixated to the anterior iris. METHODS: We studied 35 eyes in 18 patients with a preoperative myopia ranging from -6.00 to -28.00 diopters (D). The follow up ranged from 6 months (n = 15) to 12 months (n = 20). RESULTS: In 26 (74.3%) eyes, the postoperative spherical equivalent refractive error was within 1.00 D of emmetropia. The mean refraction was stable between 1 to 2 months and 12 months. The mean spectacle-corrected visual acuity improved from 20/50 to 20/40. The straylight measurements did not show a significant increase postoperatively (p = .64). The mean endothelial cell loss was 5.6% (range, +6.3% to -22.6%) at 6 months, and 8.9% (range, +0.77% to -23.5%) at 12 months. We did not encounter major complications. CONCLUSION: Implanting a Worst myopia claw IOL in high myopic eyes resulted in a stable, reasonably accurate refractive outcome. This group of patients will be followed longer because of concern over ocular complications with this technique.

Adolescent↗
PubMed1998

Effect of parental myopia on the development of myopia in Hong Kong Chinese.

A representative sample of Hong Kong Chinese children was followed from 7 to 12 years of age. Refractive error was measured every year (n = 123 at age 7 years and n = 83 at age 12 years), the axial length of the eye was measured at age 12 years (n = 81) and the refractive status of the parents was also determined. Thirty-one percent of the parents in the sample were myopic and at the age of 12 years 53% of the children were myopic. There was no association between the refractive status of the parents and whether or not a child had myopia. The probability of a 12-year-old child with early-onset myopia having at least one myopic parent was 0.55 and the probability of myopic parents having a myopic child was 0.6. There was no difference in the refractive error or the axial length of 12-year-old children according to whether neither, one or both parents were myopic. The genetic influence on myopia may be different in Caucasian and Chinese children, although it is also possible that non-expression of the genotype in the parents may have confounded the determination of the inheritance pattern of myopia in Hong Kong Chinese children.

Adolescent↗
PubMed1993

[Severe myopia or myopia-disease?].

An increased axial length over 26 mm is one of the characteristics of highly myopic eyes. High myopia represents a marked type of the refraction disorders in which distance vision is impaired and leads to wear glasses in childhood. But this high myopia is also a degenerative myopia due to the distension of the whole envelopes of the ocular bulb mainly at the posterior part of it. Prevalence of high myopia in the general population ranges from 1 to 4%. The disease is usually inherited and transmitted in a dominant fashion. Degenerative myopic eyes are potentially blind eyes due to many complications occurring during lifetime at the choroidal or retinal level. Vision threatening retinal detachments are frequent and severe, and are sometimes related to a macular hole. Other diseases including glaucoma and cataract are more frequently encountered in those eyes but may be managed with higher success. Specific oculo-motor disturbances and strabismus are also encountered. At present, the main risk threatening central vision is macular disease with lacquer cracks and hemorrhages associated with subretinal new vessels growth. Only laser photocoagulation can halt the progression of the disease and avoid or delay severe loss of central vision.

Adolescent↗
PubMed1997

Retinal function with lens-induced myopia compared with form-deprivation myopia in chicks.

BACKGROUND: The retina is known to be involved in the development of form-deprivation myopia (FDM); however, it is not clear whether the retinal changes that lead to lens-induced myopia (LIM) are the same as those involved in FDM. To gain insight into the retinal mechanism(s) that cause myopia, we investigated differences in the results of electroretinography (ERG) in eyes with FDM and LIM. METHODS: LIM or FDM was induced in chick eyes by placing various powers of spectacles or an occluder over the left eyes of 6-day-old chicks. After 6 days, the spectacles or occluder was removed, refraction and axial length were measured and ERG was performed. Results for eyes treated with spectacles and those treated with occluders were compared. RESULTS: Refraction and axial length changed concomitant with the power of the lens used, but components of the ERG of eyes with LIM were not related to the power of lens added. Refraction and axial lengths of eyes covered with a -16 D lens did not differ from these values in eyes covered with an occluder. The a- and b-waves were also similar for the two groups. However, oscillatory potentials decreased significantly in the chicks with FDM. CONCLUSIONS: Retinal function differs in LIM and FDM, as indicated by differences in the oscillatory potentials. This difference may stem from the fact that in FDM the retinal image is continuously defocused, whereas images are ultimately focused on the retina in LIM.

Animals↗
PubMed1997

[Outcome of cataract operation with reduction of myopia in myopia magna].

UNLABELLED: Patients with high myopia represent a risk group in cataract surgery. They are suspected of having a higher incidence of retina problems after cataract surgery. In addition, IOL calculations may be difficult. METHOD: In a retrospective study data of 97 eyes of 60 high myopic patients were analyzed. The inclusion criterion was an axial length of > 26 mm. All eyes underwent cataract extraction and PC IOL implantation between 1991 and 1995. Evaluation focused on visual outcome, precision of the IOL power calculation and the rate of complications. RESULTS: Visual acuity increased from 0.18 to 0.46 postoperatively. On average, myopia was reduced from -13.6 D to -3.0 D;66% of the patients were +/-1 D;86% were +/-2 D within the predicted calculation of postoperative refraction. During a follow-up period of 14.8 months no retinal detachment occurred. CONCLUSION: Cataract extraction and IOL implantation showed good functional results, and prediction of postoperative refraction was satisfactory. Our data support the studies reporting a low incidence of retinal problems in patients with high myopia.

Aged↗
PubMed1999

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

Landmark explorations by Hubel and Wiesel investigating the importance of visual impressions in postnatal development of the visual system demonstrated that neural connections and eye growth can be affected by the absence of a clear retinal image during a critical period of postnatal development. Fundamental theories on neural plasticity and deprivation have recently been established that presume that a reduced quality of the retinal image during infancy and early childhood triggers an elongation of the posterior chamber of the eye, a so-called form deprivation myopia (FDM). In a retrospective multicenter study of 187 patients who suffered from phlyctenular keratitis with corneal opacification since early childhood, we reviewed data on gender, year and age at onset of the disease, refraction, and ultrasound biometry. Compared with the average refraction of +0.5 diopter (D) found in the general population, the mean refraction of -4.43 D that we found in our study demonstrated a marked shift toward myopia of almost 5 D. Patients with an early onset of phlyctenular keratitis had considerably higher myopia (-6.68 D) than those with a late onset (-1.67 D). Additionally, an axial elongation was confirmed by ultrasound biometry. Our average, axial length was 26.53 mm, compared with the epidemiologic mean of 24.00 mm. This myopic shift of 2.53 mm was caused mainly by an enlarged vitreous cavity. These results support the finding that blur can affect eye growth and lead to FDM not only in animal experiments but also in human beings.

Age of Onset↗
PubMed1980

[Documents on the origins of myopia. 2. The genetic factor in the origin of myopia (author's transl)].

The study reported confirms that the inheritance of myopia may be autosomal-dominant as well as autosomal recessive. The recessive type starts earlier and is more serious in its course. The genes which determine myopia were found to be of low expressivity and penetrance, with some modifying factors which influence its origin. The length of the ocular axis, refractive power of the cornea, general refraction and refractive power of the lens are, in the order stated, consecutively less heritable. No genetically determined parameters of dynbamic refraction were found. The genetic factor is much more active in hypermetropia than in myopia.

Adolescent↗
PubMed2002

Nearwork induced transient myopia during myopia progression.

PURPOSE: Recent work has shown that differences exist in the accommodation response characteristics of myopes and emmetropes, although the exact nature of the differences has yet to be ascertained. This may in part be due to the classification of the refractive error employed in many studies. Previously it has been suggested that inaccuracies in the accommodation response occur predominantly during the progression of myopia.(1) To test this hypothesis we measure nearwork induced transient myopia (NITM) in progressing myopes (PMs), stable myopes (SMs) and emmetropes (EMMs). METHODS: A total of 41 young (18-27 years) subjects participated in the study (13 PMs, 14 SMs, 14 EMMs). Following a 10 minute near task (4 D) the change in accommodation response back to distance viewing was measured over a two minute time period. RESULTS: Grouped mean data revealed a significant nearwork after-effect in PMs in comparison to SMs and EMMs after 10 seconds (p < 0.01) and 30 seconds (p < 0.01) post-task. Significantly longer time constants were also found in the PMs group. CONCLUSIONS: Our results suggest that NITM is manifest during the progressive phase of myopia development.

Accommodation, Ocular↗
PubMedDate not supplied

Multicenter study of photorefractive keratectomy for myopia of 6.00 to 8.00 diopters. VISX Moderate Myopia Study Group.

PURPOSE: To summarize the initial results of excimer laser photorefractive keratectomy (PRK) on 89 eyes of 80 patients with moderate myopia (myopia of -6.00 to -8.00 diopters [D]; mean -6.98 +/- 0.90 D) at nine investigational sites. METHODS: All treatments used an argon fluoride excimer laser (VISX, Inc, Santa Clara, Calif) using standard settings. Sixty eyes received single-zone 6.0-millimeter ablations and 29 eyes received two-zone ablations. Follow up ranged from 1 month (n = 89) to 6 months (n = 46). RESULTS: At 3 months, uncorrected visual acuity measured 20/40 or better in 75% and 20/20 or better in 18%; 78% were within +/- 1.00 D of intended correction, 38% were within +/- 0.50 D, and 9% lost two or more lines of spectacle-corrected visual acuity. At 6 months, uncorrected visual acuity measured 20/40 or better in 74% and 20/20 or better in 17%; 67% were within 1.00 D of intended correction, 38% within 0.50 D, and 2% (1/46) lost two lines of spectacle-corrected visual acuity. CONCLUSIONS: PRK for moderate myopia with large diameter ablation zones appears safe and more predictable than that done using smaller ablation zone diameters. Longer follow up is needed to better define stability, the effects of postoperative corticosteroids, and the use of single-versus double-zone ablations.

Adult↗
PubMed1992

Myopia produced in young chicks by intermittent minimal form visual deprivation--can spectacles cause myopia?

Spectacle use has been postulated to aggravate or cause human myopia. Form visual deprivation, by complete full-time occlusion or refractive lenses, has been demonstrated to cause axial myopia in animals. We raised young chicks in conditions which closely approximate plano spectacle wear in humans. In addition, we sought to achieve more physiological conditions of form deprivation. Nine newborn chicks were raised with intermittent monocular visual deprivation and their eye growth and refraction monitored by retinoscopy, ultrasonic A-scan biometry and with a travelling microscope. After hatching, the nictitating membranes were sutured for 3-4 days. This was followed by a transparent plano plastic cover over the same eye for 3-4 days per week. After 3 weeks, the manipulated eyes were more myopic (mean refraction -0.72 D, axial length 13.11 mm) than fellow eyes (+0.83 D, 11.99 mm) (p < 0.05 and p < 0.01 respectively). These results suggest that the chick eye is exquisitely sensitive to disturbances in the visual environment; intermittent minimal manipulation by conditions simulating spectacle wear in man was myopiagenic. It is postulated that spectacles can cause form visual deprivation of foveal and nonfoveal neurons (and hence myopia) by reducing luminance and contrast, chromatic and spherical aberration (in nonfoveal neurons) and restriction and distortion from the frame.

Accommodation, Ocular↗
PubMed2007

Heritability and shared environment estimates for myopia and associated ocular biometric traits: the Genes in Myopia (GEM) family study.

To examine the familial correlations, heritability (h(2)) and common environmental components (c(2)) of myopia and ocular biometric traits (all treated as continuous outcomes) in families collected through the Genes in Myopia (GEM) family study in Australia. A total of 132 pedigrees (723 participants) were recruited for this study. All individuals completed a risk factor questionnaire and underwent a detailed eye examination including spherical equivalent (SphE) and ocular biometric measurements of axial length (AL), anterior chamber depth (ACD) and corneal curvature (CC). Familial correlations were calculated and h(2) and c(2) were estimated using a variance component model that assumes a multivariate t distribution within each pedigree. Two definitions of common environments (c(2)) were considered: nuclear family (current) shared environment (Model 1) and sib-ship (childhood) shared environment (Model 2). Population ascertainment adjustment was performed using the Blue Mountains eye study dataset. The trends observed for familial correlations suggested that SphE is influenced by both environmental and genetic factors whereas AL, ACD and CC are predominantly genetically determined. This was largely confirmed by variance components modelling. Heritability estimates (adjusted for age, sex and years of education) from the best fitting ACE model (Model 2, childhood shared environment) were 0.50 +/- 0.05 for SphE, 0.73 +/- 0.04 for AL, 0.78 +/- 0.04 for ACD and 0.16 +/- 0.06 for CC. Childhood environmental effects were significant with c(2) estimated to be 0.33 +/- 0.04 for SphE, 0.06 +/- 0.03 for AL, 0.22 +/- 0.04 for ACD and 0.10 +/- 0.05 for CC. Age was associated with SphE, total years of education was associated with AL and sex was associated with all traits studied. We used a novel and conservative approach to account for and estimate common environmental effects by specifying either nuclear family or sib-ship environment when estimating heritability estimates and showed that all traits examined (SphE, AL, ACD and CC) are heritable, thus reflecting a genetic component. These traits therefore all represent candidates for quantitative trait linkage analyses.

Adult↗
PubMed1979

[Evidence for the developmental theory of myopia. 1. The role of accommodation in the development of myopia].

The causal part of weakened accommodation in the formation of myopia is linked with the visual activity at near-distance. Feeble accommodation can be caused by a morphological deficiency of the ciliary muscle and its insufficient training, also by a reduced blood-supply of the eye and by the influence of general diseases on the ciliary muscle. For the first time the thought is expressed to prevent myopia and its progression by influencing the accommodative apparatus of the eye.

Accommodation, Ocular↗
PubMedDate not supplied

[Combined method for treating false myopia and preventing axial myopia].

None of the numerous methods for optic and drug treatment of the accommodation cramp effectively arrests it without long tiresome training or atropine, which limits visual working capacity for a long time and therefore, precludes starting the treatment on an outpatient basis immediately. Use of an available, simple, and effective combined method for treating the accommodation cramp helped prevent true myopia in 94.3% of young children in the main group, whereas 38.3% children in the control group developed myopia.

Accommodation, Ocular↗
PubMed1998

[Combined myopia-astigmatism correction. A comparison with pure myopia correction].

BACKGROUND: Myopic PRK up to 6 D is an approved and safe procedure. The efficacy and safety of combined treatment of myopia and astigmatism in compound myopic astigmatism (PARK) have not yet been demonstrated. PATIENTS AND METHODS: In a prospective study in 342 eyes the results of myopic PRK were compared to those of correction of compound myopic astigmatism (PARK). RESULTS: Regarding spherical refraction achieved there was no significant difference between groups. Best corrected visual acuity only improved in the group with high astigmatism; this group also showed the least number of Central Islands. Permanent haze and steroid-induced glaucoma or cataract were not observed after treatment up to 6 D. Average astigmatism of 2.24 D was be reduced to 0.53 D 1 year post-operatively. CONCLUSIONS: Correction of astigmatism resulted in undercorrection of approximately 30%. Our experience with the keracor shows PRK up to 6 D with or without additional correction of astigmatism (PARK) to be comparatively safe in terms of regression and complications and equally accurate in reaching spherical target refraction.

Adult↗
PubMed2004

Expression of pax-6 in rhesus monkey of optical defocus induced myopia and form deprivation myopia.

BACKGROUND: Pax-6 gene plays an important role in the process of eye development. This study was to determine the role of pax-6 in the axial myopia produced by hyperopic optical defocus and form deprivation in infant monkeys. METHODS: Among seven normal infant rhesus monkeys (aged 1 to 1.5 months), five wore -3.00 D spectacle lenses over their right eyes and zero-powered lenses over their left eyes. Monocular form deprivation was produced by eyelid fusion in two monkeys. Ten weeks later, the monkeys were sacrificed by an overdose of barbiturates and their eyes were removed immediately. A 5 mm x 5 mm button of retina and sclera was taken from the posterior poles along with a 4-mm optic nerve. RNA was isolated separately from each of these three types of tissues. After that, reverse transcription polymerase chain reaction (RT-PCR) was used for determining gene expression in the retina, sclera and optic nerve. Semi-quantitative analyses were performed on the PCR products. RESULTS: As expected, the optically induced hyperopic defocus and the form deprivation produced myopic growth. For the lens-treatment monkeys, pax-6 gene expression in the retinas of the defocused eyes was significantly higher than in the retinas of the left eyes (t = 5.703, P = 0.005). However, there were no analogous significant differences between pax-6 expression in the scleras or the optic nerves. For the two form-deprived monkeys, there were no obvious differences in pax-6 gene expression in the retinas or the optic nerves. CONCLUSION: The result that the expression of pax-6 was enhanced by hyperopic defocus in the infant monkey retina suggests that pax-6 may be involved in vision-dependent eye growth and emmetropization.

Animals↗