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PubMed1994

Early signs of myopia in Chinese schoolchildren.

We looked for the earliest signs of the onset of myopia in 194 emmetropic (-0.25 to +0.75 D) eyes by following them for 1 to more than 2 years. Visual acuity examination, cycloplegic retinoscopy, and A-scan ultrasonography were performed at intervals of 6 to 12 months. Of the 194 eyes 64 became myopic during the observation time. Our results show that during the progression from emmetropia to myopia the change in visual acuity is not a good indicator of the onset of myopia. When visual acuity decreased to below 6/6 (20/20) cycloplegic retinoscopy showed that most of the 64 eyes had become truly myopic and A-scan ultrasonography revealed a significant increase in vitreous chamber depth and axial length as compared to the non-myopic eyes. In the early stage of myopia development the anteroposterior diameter of the eye elongates. However, changes in anterior chamber depth and lens thickness did not differ between the myopic and non-myopic group. Our results suggest that routine ocular refraction should be conducted in addition to the school vision screening. For those who have visual acuity 6/6 (20/20) and ametropia of -0.25 D or more minus we would like to be able to prevent or at least retard the development of myopia.

Child↗
PubMed1996

Myopia associated with hyperbaric oxygen therapy.

BACKGROUND: Hyperbaric oxygen therapy (HBOT) involves exposing patients to elevated oxygen pressures and concentrations for the treatment of soft tissue degenerative diseases. As side effects, some patients experience cataract development and/or a significant increase in myopia. SUBJECTS: Eight subjects participated in this project. All were receiving HBOT for health problems. METHODS: For all subjects, acuities and refractive error corrections were measured before and after HBOT sessions at the beginning, midpoint, and end of therapy. For four subjects, A-scan ultrasound and corneal curvature measurements were also made before and after selected HBOT sessions. In addition, susceptibility to free radical damage and indicators of actual damage were measured by blood analyses. During the first half of HBOT therapy, four subjects took placebo tablets; during the second half, antioxidant supplements were given. RESULTS: No subject showed significant acuity or refractive error changes produced by single HBOT sessions. Two of the 8 subjects showed significant increases in myopia over the 20 session course of HBOT. No corresponding changes were found in the ultrasound, corneal curvature, or blood analysis data. DISCUSSION: Theoretically, the increases in myopia could have been caused by lenticular refractive index changes resulting from oxidative damage to lens proteins. However, the biochemical assays used in this project did not predict which subjects were susceptible to increased myopia, nor did they demonstrate elevated levels of free radical activity in a subject who did experience an increase in myopia.

Adult↗
PubMed1999

Factors associated with the prevalence of myopia in 6-year-olds.

PURPOSE: To describe the frequency of and risk factors associated with myopia in grade one children. METHODS: Refractive error was measured by static retinoscopy, without cycloplegia, for 10,616 children in the first year of a province-wide vision-screening program. Information on factors that might be associated with myopia was collected from parents or guardians by self-administered questionnaires distributed before the vision screening. These factors were evaluated by a case-control method. RESULTS: The prevalence of myopia, greater than -0.25 D, was 6%. The estimated relative risk of myopia was increased significantly among children whose birth weight was <2500 g and whose mothers had a history of early spectacle use. CONCLUSIONS: Results suggest that the prevalence of myopia in 6-year-old children is associated with both hereditary and nonhereditary factors. In accord with prior work, the results argue that low birth weight has a permanent influence upon eye development.

Age Factors↗
PubMed1999

Progression of myopia in Hong Kong Chinese schoolchildren is slowed by wearing progressive lenses.

PURPOSE: In Chinese societies, primary and secondary schoolchildren perform large amounts of reading and homework and thus spend long periods performing near work during their growth years. Progressive lenses, which can permit a focused retinal image at distance, intermediate, and near, without accommodation, may slow the development of myopia. This paper reports results of a 2-year longitudinal study to examine the effects of progressive lenses on myopia progression in myopic Chinese children; these children were aged between 9 and 12 years at the beginning of the study. METHODS: Prestudy vision screening tests and five examinations, which included noncycloplegic refraction, were conducted at half-yearly intervals. Of those who completed the study, 32 children wore single vision (SV) lenses (the SV group) and 36 wore progressive lenses; of the latter, 22 wore a +1.50 D addition (the P1 group) and 14 wore a +2.00 D addition (the P2 group). Refractive error, corneal curvature, axial length, vitreous depth, and intraocular pressure were measured at every examination. Height was measured as an index of general growth. RESULTS: Progressive lenses significantly retarded the progression of the myopia in these children. Initially, the mean refractive error of the SV group was -3.67 D, of the P1 group was -3.73 D, and of the P2 group was -3.67 D. The mean myopic progressions over the 2 years of the study were -1.23, -0.76, and -0.66 D for the SV, P1, and P2 groups, respectively. CONCLUSION: Progressive lenses reduce the progression of myopia. It may be that the interaction of the progressive lenses with the accommodation system is the cause of this reduction in myopia progression because the +2.00 D addition appeared more effective than the +1.50 D addition in slowing the progression.

Child↗
PubMed2000

A randomized trial of the effect of single-vision vs. bifocal lenses on myopia progression in children with esophoria.

BACKGROUND: Bifocals have long been thought to reduce progression of childhood myopia. However, this hypothesis has not been definitively evaluated. METHODS: We conducted a randomized clinical trial to test the hypothesis that bifocals slow myopia progression in children with near-point esophoria. Eighty-two myopic children were randomized to single-vision glasses (n = 40) or to bifocals with a +1.50 D add (n = 42) and were followed for 30 months. Refraction was measured by an automated refractor after cycloplegia. The primary outcome was myopia progression defined as the difference between the spherical equivalent at baseline and at the 30-month examination, averaged over both eyes. RESULTS: Follow-up was incomplete for six children in the bifocal group and one child in the single-vision group. Among the children completing the 30 months of follow up, myopia progression (mean spherical equivalent of the two eyes) averaged 0.99 D for bifocals and 1.24 D for single vision (unadjusted, p = 0.106; adjusted for age, p = 0.046). Treatment groups differed in their cumulative distributions (Kolmogorov-Smirnov procedure, p = 0.031). Evidence for a treatment effect on growth in vitreous chamber depth was similar (p = 0.046 by K.S.). CONCLUSION: Use of bifocals, instead of single-vision glasses, by children with near-point esophoria seemed to slow myopia progression to a slight degree.

Aging↗
PubMed2000

Temporal variations in myopia progression in Singaporean children within an academic year.

PURPOSE: Excessive nearwork is believed to be associated with myopia development and progression. To investigate this further, we studied refractive error changes and their correlation with nearwork in a cohort of grade school children in Singapore. METHODS: Cycloplegic autorefraction was performed 5 times over 10 months on 168 children aged 7, 9, and 12 years who were further divided into myopic and nonmyopic subgroups based in their initial refractive errors. Information about nearwork was obtained through diaries filled out over 24 h at the commencement of the study. RESULTS: Myopia progression was high (overall mean: -0.87 D per year) and largely linear throughout the year, but significantly higher rates were seen after the final school examinations in 7-year-old myopes and nonmyopes. Overall, myopic groups exhibited higher progression rates than nonmyopic groups, although 33.6% of subjects from the latter groups had become myopic by the end of the study. Nearwork scores derived from the diaries were generally not well correlated with overall myopia progression. CONCLUSIONS: The tendency for myopia progression rates to increase after the final school examinations in 7-year-olds is interpreted as a delayed effect of the intense nearwork associated with preparing for them. The timing of nearwork-diary data collection at the beginning of the study could be responsible for the poor correlation between these data and overall myopia progression rates.

Child↗
PubMed2002

Seasonal variation in myopia progression and ocular elongation.

PURPOSE: To evaluate possible seasonal variations in myopia progression and ocular elongation in school children. METHODS: Seventy-one children who were enrolled in a clinical trial of bifocals were examined every 6 months for 30 months. Three 6-month intervals ("winters") included none of the summer vacation from school, and two intervals ("summers") included all of the summer vacation. Myopia was evaluated, after cycloplegia with 2 drops of 1% tropicamide, by automated refractor, and changes in axial length and in vitreous chamber depth were measured by A-scan ultrasonography. Data from left and right eyes were averaged because there was no evidence of a significant eye-visit interaction. Analysis of variance with a planned contrast was used to evaluate differences between the observed rates of change over the two summers compared with expected rates assuming no seasonal effect. RESULTS: For 37 children in single-vision lenses, myopia progression rates over the two summers averaged 0.15 D compared with 0.32 D over the three winters. For 34 children in bifocal glasses, summer rates averaged 0.07 D compared with 0.30 D for winters. Analysis of variance showed that seasonal effects on myopia progression were significant (p < 0.025) for both groups for the first summer and approached significance for the second summer. Increases in vitreous chamber depth were also slower during the summer, significantly so (p < 0.01) for both summers in the single-vision group and for the second summer only in the bifocal group. Changes in axial length were somewhat slower in the summer, but the effect of season reached statistical significance in that variable only for the second summer in the bifocal group (p = 0.031). CONCLUSION: Myopia progression rates were slower during the 6-month periods that included all of the summer vacation than would be expected assuming no seasonal effect. Ocular growth was also slower in the summer; but that trend, in most cases, was statistically significant only for changes in vitreous chamber depth and not for axial length.

Child↗
PubMed2004

Changes in myopia with low-Dk hydrogel and high-Dk silicone hydrogel extended wear.

PURPOSE: This study compared changes in myopia between wearers of high-oxygen permeability (Dk) silicone hydrogel lenses and low-Dk hydrogel lenses after 1 year of extended wear (EW). METHODS: Ninety-two adult subjects were randomly assigned to a lens type. Subjective refraction and autokeratometry were performed at baseline and at 6 and 12 months. RESULTS: After 6 months of EW, myopia (spherical equivalent) regressed by 0.18 +/- 0.33 D (p < 0.001) in the high-Dk silicone hydrogel group and progressed by -0.23 +/- 0.36 D (p < 0.001) in the low-Dk hydrogel group. There were no further changes after 12 months. Previous lens wear history, baseline refractive error, and age and gender did not have an impact on the change in myopia, and only 35% of the variation could be accounted for by changes in corneal curvature and lens type. CONCLUSION: Soft contact lens type significantly affects the direction of change in myopia during EW. We hypothesize that these changes are driven by pressure-related redistribution of corneal tissue in high-Dk silicone hydrogel lens wearers and by hypoxia-associated corneal thinning in low-Dk hydrogel wearers. More long-term studies are required to confirm whether the effects of high-Dk silicone hydrogel lens wear on myopia are permanent.

Adult↗
PubMed2004

Screening for myopia and refractive errors using LogMAR visual acuity by optometrists and a simplified visual acuity chart by nurses.

PURPOSE: To compare the sensitivity and specificity of a widespread method of screening for refractive errors in Singapore schoolchildren using a simplified acuity screening chart with a more rigorous method using the Early Treatment Diabetic Retinopathy Study (ETDRS) chart. A secondary aim is to estimate the best cutoff values for the detection of refractive errors using these two methods. METHODS: This is a population-based study, involving 1779 schoolchildren from three schools in Singapore. Logarithm of the minimum angle of resolution (logMAR) visual acuity was recorded using a modified Bailey-Lovie chart by trained optometrists, and visual acuity measurement was also undertaken using a simplified 7-line visual acuity screening chart by school health nurses. The main outcome measures were the receiver-operating characteristics (ROC's) of logMAR and the simplified screening visual acuity to detect myopia or any refractive errors. The difference between measurements, simplified screening visual acuity--logMAR visual acuity, was calculated. RESULTS: The optimal threshold using the simplified screening visual acuity chart for the detection of myopia or any refractive error was 6/12 or worse. Using logMAR visual acuity, the most efficient threshold for the detection of myopia was 0.26, but this was 0.18 for the detection of any refractive error. The area under the ROC curves was significantly greater in the case of the logMAR visual acuity measurement compared with the simplified screening visual acuity measurement for the detection of myopia or any refractive errors. The 95% limits of agreement for the two methods (simplified screening--logMAR acuity) was -0.219 to +0.339. CONCLUSIONS: Bearing in mind that the visual acuity measurements were performed by two different groups of professionals, visual acuity screening using the ETDRS method appears to be more accurate than the simplified charts for the detection of myopia or any refractive errors in children.

Child↗
PubMed2005

The association of astigmatism and spherical refractive error in a high myopia cohort.

PURPOSE: The purposes of this study were to determine whether the degree of myopia influences the presence and degree of total astigmatism, and to assess risk factors of astigmatism in patients with familial nonsyndromic severe myopia. METHODS: We performed a retrospective study of 217 subjects from families with two or more subjects from successive generations with a myopic spherical refractive error of at least -5 D or greater in one eye. Mean myopic spherical equivalent was -10 D and the mean age of myopia onset was 7 years. Refractive error measurements were obtained and the association between the degree of myopia and cylinder power was examined by correlation analysis. RESULTS: The prevalence of astigmatism (1.0 D of cylinder) was 36.1%. With-the-rule astigmatism was most common (55.8%), and the majority of astigmats had between 1.0 and 2.5 D of cylinder (77.6%). Statistically significant associations were found between the presence of astigmatism and risk factors of age and the age of myopia onset. In those patients with astigmatism, however, there was a moderate correlation between the degree of spherical equivalent and cylinder power (r = -0.34, p < 0.0001). Younger age (<16 years) (p = 0.03) was associated with higher cylinder power. CONCLUSIONS: In severely myopic patients, there is a high prevalence of astigmatism that is predominantly with-the-rule. The degree of myopic spherical refractive error is correlated with astigmatism severity but is not a risk factor for the presence of astigmatism.

Adolescent↗
PubMed2003

Molecular biology of myopia.

Experiments in animal models of myopia have emphasised the importance of visual input in emmetropisation but it is also evident that the development of human myopia is influenced to some degree by genetic factors. Molecular genetic approaches can help to identify both the genes involved in the control of ocular development and the potential targets for pharmacological intervention. This review covers a variety of techniques that are being used to study the molecular biology of myopia. In the first part, we describe techniques used to analyse visually induced changes in gene expression: Northern Blot, polymerase chain reaction (PCR) and real-time PCR to obtain semi-quantitative and quantitative measures of changes in transcription level of a known gene, differential display reverse transcription PCR (DD-RT-PCR) to search for new genes that are controlled by visual input, rapid amplification of 5' cDNA (5'-RACE) to extend the 5' end of sequences that are regulated by visual input, in situ hybridisation to localise the expression of a given gene in a tissue and oligonucleotide microarray assays to simultaneously test visually induced changes in thousands of transcripts in single experiments. In the second part, we describe techniques that are used to localise regions in the genome that contain genes that are involved in the control of eye growth and refractive errors in mice and humans. These include quantitative trait loci (QTL) mapping, exploiting experimental test crosses of mice and transmission disequilibrium tests (TDT) in humans to find chromosomal intervals that harbour genes involved in myopia development. We review several successful applications of this battery of techniques in myopia research.

Animals↗
PubMed2006

Analysis of refractive state ratios and the onset of myopia.

PURPOSE: To develop formulae for the refractive state ratios, axial length growth and the age of onset (A*) of myopia. Calculated results are compared with measurements. METHODS: Using an image equation, the axial length in the ametropic state (L) is related to the length in the emmetropic state (L*) and refractive error (D) by a rate of change M (D mm(-1)). Three refractive state ratios are defined: C1 = L/r1, C2 = L/L* and C3 = L/H, where r1 and H are the anterior surface radius of the cornea and the transverse dimension of the eye, respectively. The age of onset A* is calculated by the rate of change of refractive error (M) and the axial growth rates N and N* in the ametropic and emmetropic states, respectively. RESULTS: The three ratios C1, C2 and C3 are increasing function of the myopia power, for example, C1 = 3.4, 3.1, 2.9 for D = -8, 0, +4 dioptres, respectively. The calculated C1* (for the emmetropic state) varies between 3.08 and 3.14, depending on corneal shape, and C3 = 0.985, 1.0, 1.04 for D = +3, 0, -3 dioptres: these values are consistent with measured data. For a typical system with effective focal length F = 22.25 mm, L* = 24.2 mm and L = 23.4, 24.9, 25.9 mm for D = +2, -2, -5 dioptres, respectively. The calculated rates of change of refractive error M = 2.3-2.9 D mm(-1) for F = 22-23 mm are also consistent with measured values 2.4-2.7 D mm(-1). The age of onset A* is calculated to be proportional to 1/(M dN), where dN = N-N* is the axial growth rate difference between the ametropic and emmetropic states and may be used as a better predictor for myopia onset than the conventional ratio L/r1. The A* is given by the crossing of L and L* curves, in which myopia onset occurs earlier for larger M dN. CONCLUSION: The theory provides formulae to calculate various refractive state ratios, which are consistent with measurements. By defining two rate functions, M and N, the onset of myopia can be predicted.

Age of Onset↗
PubMed1996

Pre-term delivery and subsequent ocular development. A 7-10 year follow-up of children screened 1982-84 for ROP. 3) Refraction. Myopia of prematurity.

Refractive findings are reported in a follow-up study comprising 88 children aged 7-10 years, who were submitted to regular control for retinopathy of prematurity (ROP) in the first months after their pre-term delivery 1982-84 (mean birthweight 1467 g, mean gestational age 31 weeks). The refractive range was -13 to +6.75 D. In four subjects with fully-blown ROP both eyes were left blind and dysmorphic. Twenty-four had had ROP with regression; myopia of prematurity (MOP) appeared in six (25%). At follow-up the myopia frequency in the remaining 60 without ROP was 5%. Out of the 9 subjects with uni- or bilateral myopia of prematurity three had no evidence of early ROP. With a median corrected acuity of 0.5 only, the eyes with MOP had a lower corrected visual score than in the rest of the material (median monocular acuity 0.9). The latter value is even a little lower than what was previously reported in full-terms of a similar age (median acuity above 1.0). Obviously, as a sequel to the pre-term delivery we are dealing not only with early myopia in some subjects; further, the potential for developing full vision appears influenced and reduced. This applies to the total group of ex-prematures, but in particular it is valid for myopia of prematurity.

Child↗
PubMed1983

Is myopia getting more frequent? A cross-sectional study of 1416 Danes aged 16 years+.

A hospital material considered refractively unselected is made up by adult patients referred for general eye examination from other (non-ophthalmic) departments (n = 1416; 2832 eyes). Thirty per cent of all eyes had negative refractive value. The highest myopia prevalence, about 40%, was seen in the age group 26-45 years. Glass-demanding myopia (of at least -0.75 D) occurred in 14% of the elderly (66 years +) against 27-28% in younger adults. Up to the age of 45, more females were myopic than males. The present prevalences are considerably higher than expected from previous Danish studies. It is discussed to what extent this increase is real. The diabetes of the sample (representing 762 eyes) show a shift towards negative refractive values (37.9% with myopia) as compared to non-diabetics (27.5%). The diabetic surplus is due to low degree myopia cases. The association between myopia and (well-controlled) diabetes seems to be a new observation.

Adolescent↗
PubMed1988

Permeability of the blood-retinal barrier in myopia. An analysis employing vitreous fluorophotometry and computer simulation.

Vitreous fluorophotometry was performed in 165 eyes of 93 cases with various degrees of myopia. The age range was 10-39 years. On background of the significant correlation between the refractive diopter value and the length of vitreous cavity, a simulation model for myopia has been established for assessing the permeability of the blood-retinal barrier. Significant negative correlations between the diopter and P-in and the diopter and D-p were found, indicating that by increasing degree of myopia, the functional disorder of the blood-retinal barrier and the liquefaction of the posterior vitreous gel progress. From the comparative study between eyes with slight myopia and eyes with emmetropia, a significant increase in the length of the vitreous cavity and P-in was found in the former, whereas no significant difference was observed in D-p. Therefore, it is suggested that the functional disorder of the blood-retinal barrier in myopia produces the liquefaction of the posterior vitreous gel.

Adolescent↗
PubMed2006

Central corneal thickness and its relationship to myopia in Chinese adults.

AIM: To investigate the association between central corneal thickness (CCT) and the degree of myopia among Chinese. METHODS: In this prospective observational study, 714 consecutive patients were recruited from a refractive surgery clinic. CCT was measured in both eyes of each patient using the Orbscan (Bausch and Lomb, Rochester, New York, USA), and data of the right eye were selected for analysis. CCT was correlated with the degree of myopia in dioptres (D) using Pearson's correlation coefficient and Dunnett's t test with multiple comparisons. RESULTS: The age of the patients ranged from 15 to 59 years. The mean CCT was 534.5 microm, with a standard deviation (SD) of 38.1 (range 305-684) microm. The mean (SD) myopic spherical equivalent was 5.30 (2.74) D, range -17.5--0.625 D. No correlation was found between CCT and the degree of myopia (r = -0.13, p = 0.719). CONCLUSIONS: Among Chinese with myopia, CCT was distributed over a large range but did not correlate with the degree of myopia.

Adolescent↗
PubMed1976

Early and late results of fascia lata transplantation in high myopia.

Transplantation of a strip of fascia lata to strengthen the posterior sclera in high progressive myopia was performed on 184 eyes of 108 patients with myopia ranging from 7 to 39 D. Three weeks after surgery visual acuity with correction had improved by 0-1 to 0-5 in 151 eyes (82 per cent) and refractive power had decreased by 1 to 8 D in 169 eyes (92 per cent). In 105 eyes (67 patients) that were followed-up for periods of from 1 to 9 years myopia increased in six by 0-5 to 3 D. In 29 patients who had an operation on only one eye and were then followed-up for periods of from 1 to 7 years the degree of myopia in the fellow eye increased by 1-5 to 6 D in 24 (83 per cent), and of the eyes that were operated on myopia increased by 0-5 to 3 D in only 5 (17 per cent).

Adolescent↗
PubMed1987

Cataract: the relation between myopia and cataract morphology.

The association between high myopia and cataract is already well established and an association between simple myopia and cataract has been suggested, but it has not been clear to what extent the myopia precedes the cataract or is the result of it. The present study compares the refraction of a group of 100 British patients at the time of first presentation with cataract in whom the refraction was also known four years previously, with a group of matched controls in whom the refraction was also known four years previous to presentation. The study shows that simple myopia does not appear to predispose to cataract. It is the development of the cataract itself, in particular nuclear sclerosis, which causes the refractive change towards myopia. The myopic change precedes the development of cataract, and patients over the age of 55 showing a myopic change in refraction have a very high probability of developing nuclear sclerotic cataract. The healthy aging eye and eyes with cortical cataract or subcapsular cataract, but without nuclear sclerosis, continue to show a gradual hypermetropic change with time.

Adult↗