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PubMed2006

[Myopia and genetics].

The physiological manifestation of myopia is error of refraction. The incidence of myopia in Asian population is increasing much more rapidly compared with several decades ago. Most of the people in the relatively developed Chinese cities are developing or have developed myopia. Recently, researches reported six loci related to myopia. Viewing from the modern civilization and development of China, the sharp increase of the size of the population with myopia and the unbalanced change could not be explained only by gene mutation or any model of Mendelian inheritance. The comparison of the disparity of the economic and educational levels between in urban and rural areas showed that the onset of myopia might be influenced by both environmental and genetic factors. Special attention should be paid to myopia now to prevent severe physical problem in the Chinese urban population.

China↗
PubMed2006

The association of single nucleotide polymorphisms in the 5'-regulatory region of the lumican gene with susceptibility to high myopia in Taiwan.

PURPOSE: To study the relationships between single nucleotide polymorphisms (SNPs) of lumican, decorin, and DSPG3 genes and high myopia. METHODS: One hundred and twenty adult patients with high myopia (< -10.0 D) and 137 controls were used to study the relationships between the decorin, lumican, and DSPG genes and high myopia. All subjects were free of ocular diseases, other than myopia, as well as of other systemic genetic diseases. Genotyping was performed by direct sequencing after PCR amplification of chromosomal DNA. Allele frequencies were tested for Hardy-Weinberg disequilibrium. The chi(2) or Fisher test was conducted to investigate the genotypic and allelic distribution between the high myopia and control groups. RESULTS: The genotyping success rate was 100%. Univariate analysis revealed significant differences between patients and control subjects with respect to one of the SNPs (rs3759223, C->T) of the lumican gene, with a p value of 0.000283. There was no significant relationship between other SNPs of lumican, decorin, and DSPG genes and high myopia. CONCLUSIONS: Our results indicate that an SNP (rs3759223), which is located in the promoter region of the lumican gene, may be worth further investigation to determine its association with development of high myopia.

5' Flanking Region↗
PubMed1991

[Myopia--a disease or a physiological defect?].

Many investigations have been carried out during the last 150 years to detect factors which cause nearsightedness (myopia). A factor that has been awarded particular attention in addition to hereditary factors is the influence of the environment, especially the amount of close work on the refractive state of the eye. The increasing prevalence of myopia among children and young people revealed in some populations has been related to stressing educational systems, which are suspected of enhancing the changes in the growth of the eye leading to myopia. However, the direct etiological relationship between the myopia and prolonged accommodation during the close work has still to be established. The prevalence of myopia in Norway is not known, but relatively high prevalence was found in a recent study among medical students and physicians. At the present time, increasing interest is being shown for keratorefractive surgery to correct myopia. Both radial keratotomy and excimer laser photorefractive keratomileusis have become available in Norway, and a few hundred patients have been operated. The purpose of this article is to elucidate some important aspects in understanding the etiology, development and correction of myopia.

Eye↗
PubMed1994

Progression of myopia in different ethnic groups in Malaysia.

A cross-sectional study on a normal clinical myopic population reveals that there is a difference in the pattern of myopic progression between Malays and Chinese in Malaysia. It shows that while myopia in Malays stays relatively constant throughout 10 to 50 years of age, myopia in Chinese progresses rapidly from 10 to 20 years of age, after which it starts to show hyperopic shift, reaching a level of myopia similar to that of Malays at around 35 years of age. In view of the above finding it is postulated that the difference in myopia between the two races may be due to excessive accommodation in Chinese, causing a temporary increase in crystalline lens power and hence an increase in myopia. Because the magnitude of myopia for both races for 10 +/- 1 years age group is relatively high, i.e. about -2.00 D, it is postulated that myopia in these ethnic groups may start much earlier than 10 years of age.

Adolescent↗
PubMed1993

Race, culture and Myopia in 110,236 young Singaporean males.

Computerised data of 110,236 Singaporean males aged 15 to 25 (mean 17.75) years who underwent compulsory medical examination from April 1987 to January 1992 was used to estimate the prevalence of myopia among young Chinese, Malay, Indian and Eurasian Singaporean males. The prevalence of myopia amongst the different racial groups was compared after they had been matched for important known confounding factors such as age, sex, educational attainment and degree of urbanization of place of residence. The estimated myopia prevalence was 48.5% in Chinese, 34.7% in Eurasians, 30.4% in Indians and 24.5% in Malays. The overall myopia prevalence rate for all races combined was 44.2%. Within each educational group, the Chinese generally had the highest myopia prevalence whilst the Malays generally had the lowest. Myopia prevalence among the Indians tended to be between that of the Chinese and the Malays. Having matched the various racial groups for age, sex, educational attainment and degree of residential urbanization, it would appear that racial and cultural differences are major influences responsible for the difference in myopia prevalence observed amongst the different races.

Adolescent↗
PubMed1993

Biomechanical considerations of high myopia: Part I--Physiological characteristics.

Prior to a discussion of biomechanical considerations in high myopia, a review of anatomical and physiological patterns in high myopia is presented. A scleral pathogenesis or mesodermal hypothesis of the anomaly is presented with the inclusion of supporting evidence. Retinal, choroidal, and vitreous malformations in high myopia also are highlighted. Notable is a pattern consistent with the concept of gradual stretching of the vitreous chamber. The association of high myopia with other diseases is shown, with special attention being given to the concomitant features of high myopia and glaucoma. A discussion of animal deprivation studies examines their relevance to cases of clinical myopia. The dopamine deficit found in the retinas of visually deprived animals appears to be an area that will attract considerable future research. However, there may be no connection of these experimental findings in deprived animals to most cases of high myopia.

Biomechanical Phenomena↗
PubMed1993

[Natural development of myopia in indications for scleroplasty surgery].

The authors submit a report on investigation of progressing myopia in children and adults meeting the criteria for indication of scleroplastic surgery. However, the operation was not performed. In children with myopia gravis (5 eyes) the progression of myopia in the course of six years was 1.1 +/- 1.02 D, in children with myopia progressiva (14 eyes) 2.9 +/- 1.4 D/6 years. In adults with myopia gravis (96 eyes) the progression in 6 years was 1.5 +/- 1.9 D, in adults with myopia progressiva (7 eyes) the progression in 6 years was 1.1 +/- 1.2 D. The difference in the two groups was statistically significant at the 1% level. It is necessary to seek procedures to prevent progression of myopia to higher values.

Adult↗
PubMed1996

The M1 muscarinic antagonist pirenzepine reduces myopia and eye enlargement in the tree shrew.

PURPOSE: To determine the efficacy of the M1-selective muscarinic antagonist, pirenzepine, in preventing experimentally induced myopia in a mammalian model, the tree shrew. METHODS: Tree shrews were monocularly deprived (MD) using translucent goggles or negative lenses for a period of 12 days. In two of the MD groups, tree shrews received daily subconjunctival administration of either pirenzepine (17.7 mumol; n = 9) or vehicle control (n = 6). Control groups (n = 6) were used to assess the effects of MD, injection regimen, and drug effects. RESULTS: In sham-injected and saline-injected MD tree shrews, 12 days of MD produced-13.2 D +/- 0.8 D and -14.1 D +/- 0.5 D of axial myopia, respectively. In pirenzepine-injected MD tree shrews, 12 days of MD induced an axial myopia of only -2.1 D +/- 1.4 D. The significant reduction in myopia in pirenzepine-injected MD tree shrews was caused by significantly less vitreous chamber elongation of the deprived eye (0.05 mm +/- 0.04 mm) relative to the contralateral control eye when compared to sham-injected and saline-injected MD tree shrews (0.24 mm +/- 0.02 mm and 0.29 mm +/- 0.01 mm). Mean equatorial enlargement and increased eye weight were prevented in pirenzepine-injected MD tree shrews (P < 0.01). Pirenzepine also was found to reduce myopia and ocular enlargement in lens defocus-induced myopia. Control experiments demonstrated that pirenzepine did not cause a significant reduction in amplitude of carbachol-induced accommodation. CONCLUSIONS: Findings demonstrate that chronic administration of the M1-selective muscarinic antagonist, pirenzepine, prevents experimentally induced myopia in this mammalian model by a nonaccommodative mechanism.

Accommodation, Ocular↗
PubMed1996

Can bifocals slow myopia progression?

BACKGROUND: Retrospective studies have suggested that in children with near point esophoria, bifocals can slow myopia progression by about 50 percent. A prospective study was conducted to test this hypothesis. METHODS: Thirty-two children, all with near point esophoria, were randomly divided into either correction with single-vision or with bifocal lenses containing a +1.25 D and. Axial length and refraction were measured under cycloplegia every 6 months for 18 months. Twenty-eight children completed the study. RESULTS: Myopia progressed at an equal rate in both groups for the first 12 months. Progression was much faster during the first 6 months, which was during the school year, than during the second 6 months, which included all of the summer vacation (0.64 D/yr vs 0.29 D/yr). During the last 6 months, myopia progressed rapidly for children in single-vision lenses (0.80 D/yr) but slowly for those in bifocals (0.37 D/yr). A repeated-measure analysis of variance showed that season of the year had a significant effect on myopia progression (p > 0.002) and that the effect differed for the two treatment groups (p > 0.043). Over the whole 18-month study, myopia progressed at rate of 0.57 D/yr for those in single-vision lenses and 0.39 D/yr in those in bifocals (p = 0.26). CONCLUSIONS: Bifocals seemed to slow myopia progression in these children with near-point esophoria, although a longer-term study with more subjects is needed to confirm this finding. Myopia progressed more rapidly during the school year than during summer vacation.

Adolescent↗
PubMed2006

Characteristics of peripapillary detachment in pathologic myopia.

OBJECTIVE: To evaluate the prevalence and clinical features of a newly recognized peripapillary lesion specific to high myopia, peripapillary detachment in pathologic myopia (PDPM), in a large series of patients with high myopia. METHODS: Three hundred twenty-four patients (632 eyes) with high myopia were enrolled in this study. We examined the prevalence, range, fluorescein and indocyanine green angiographic findings, and optical coherence tomography findings of PDPM for these patients. Visual field testing (Goldmann kinetic perimetry and the Humphrey 30-2 program) was also performed in the patients with PDPM. RESULTS: Peripapillary detachment in pathologic myopia was identified in 31 of 632 highly myopic eyes (4.9%). The optical coherence tomographic scan across the PDPM lesion revealed a localized detachment of retinal pigment epithelium adjacent to the optic nerve. Although PDPM was always situated adjacent to the inferior edge of the optic disc, in some patients it surrounded almost the entire optic disc. There was a steep excavation of the inferior myopic conus adjacent to the PDPM, and the inferotemporal retinal vein was markedly bent at the transition from the PDPM to the excavated myopic conus. Glaucomatous visual field defects were frequently detected in eyes with PDPM (71.0%). CONCLUSIONS: The findings of this study indicate that PDPM is not uncommon among highly myopic eyes. Although its pathogenesis and pathologic significance require further classification, PDPM might be another indicator of visual field defects in high myopia.

Adolescent↗
PubMed1993

The correction of high myopia using the excimer laser.

OBJECTIVE: To determine the safety and efficacy of excimer laser photoablation as a treatment to correct high myopia that is defined as a spherical equivalent refractive error greater than -8.00 diopters (D). DESIGN: Using a multizone (4.0-, 5.0-, and 6.0-mm) photorefractive keratectomy protocol for correction of high myopia, 23 eyes in 18 patients were treated at one clinical center with an excimer laser (VISX Inc, Santa Clara, Calif). Preoperative spherical equivalent refractions ranged from -8.00 to -19.50 D (mean +/- SD, -11.83 +/- 2.92 D); the mean attempted ablation depth was 93.0 +/- 20.2 microns. RESULTS: At the last postoperative examination (mean +/- SD, 7.5 +/- 3.7 months), the mean +/- SD spherical equivalent refraction was -1.09 +/- 2.08 D, including results from two repeated procedures; visual acuity in 52% of the eyes was 20/40 or better uncorrected; 65% of the eyes improved or did not change best corrected acuity, whereas two eyes lost 2 Snellen lines; 39% of the eyes were +/- 1.00 D; and 65% were +/- 2.00 D of attempted correction. Corneal haze (corneal clarity score of > or = 1.5) was observed in 47% of the eyes at some time postoperatively. CONCLUSIONS: Photorefractive keratectomy for high myopia was found to be not nearly as efficient or predictable as it is for low myopia. A greater incidence of regression of refractive effect and corneal haze were noted in these cases compared with reported studies of low to moderate myopia. A multizone approach to reduce ablation depth during photorefractive keratectomy for myopia that is greater than 8.00 D does not appear to prevent subsequent haze or refractive regression.

Adult↗
PubMed1990

Myopia in humans: can progression be arrested?

The multiplicity of theories regarding the aetiology of myopia has led to numerous and partly contradictory methods of therapy. Interest has been focused on accommodation because of the established association between myopia and close work. In studies of drug treatment of myopia, the treatment is often reported to be effective but the lack of randomization and high drop-out rates make the results questionable. In the Soviet Union, scleral reinforcement is said to be highly successful. Bifocal spectacle lenses reduce the accommodative demand, but studies on the effect of bifocal lenses have shown widely varying results. Whether contact lenses are effective in the control of myopia is still uncertain. In a Danish prospective study on the effect of treatment with bifocal lenses and beta-blocker eye drops a lower rate of progression was found among children wearing bifocal lenses but the difference from the control group was too small to warrant the use of such lenses in every myopic child. The progression rate in the group treated with the beta-blocker timolol maleate was not different from that in the control group. There thus seems to be no simple way of stopping or reducing the progression of myopia. Epidemiological data indicate that the maximum incidences of myopia are associated with educational systems in which the demands on the ability of the child to learn are stringent. One might introduce the term 'ocular stress' but this is clearly difficult to define and even more difficult to measure.

Contact Lenses↗
PubMed1990

Retinal influences on sclera underlie visual deprivation myopia.

Visual deprivation of chicks rapidly induces an increased growth of the vitreous chamber which results in axial myopia, even after a day or so. This experimental myopia provides an opportunity to trace the causal path from altered visual experience to altered eye growth. With respect to the visual factors involved, the gross activity of the retinal neurons seems an important variable. The eyes of animals raised wearing translucent occluders do not become myopic or elongated if stroboscopic illumination is present. Conversely, the eyes do become myopic and elongated if deprived of all form vision, if reared in a featureless environment or if deprived in only part of the visual field. The deprivation must, however, be continuous if myopia is to result; even as little as two hours of normal vision per day almost completely eliminates the effect of 12 hours of deprivation. The control of eye growth by vision seems to take place in local regions of the eye. Deprivation of various parts of the visual field produces myopia and elongation in only the deprived part, even in animals in which the optic nerve has been cut. It seems that at the level of the sclera ocular elongation (and thus myopia) results from local growth, because we find increases in synthesis of DNA and protein as well as more new cells. The protein synthesis increase is also local, in the sense that the posterior sclera grows much more than other parts, explaining why deprivation causes ocular elongation and myopia, rather than simply larger eyes. These results suggest that some factor in part of the retina can influence the growth of the subjacent sclera.

Animals↗
PubMed1999

Interactions of spatial and luminance information in the retina of chickens during myopia development.

Degrading the retinal image by frosted eye occluders produces elongated eyes and 'deprivation myopia' in a variety of animal models. The postulated retinal 'deprivation detector' is quite sensitive to even small changes in image contrast or spatial frequency composition. Because psychophysical experiments have shown that a decline in luminance shifts the contrast sensitivity function to lower spatial frequencies, it is likely that only a reduced spatial frequency range is available for image analysis to control eye growth. It is even possible that the compression might be sufficient to promote deprivation myopia. We have tested this hypothesis, using the animal model of the chicken. (1) At an ambient illumination of 550 lux (about 76 cd m-2), neutral density (ND) filters placed in front of the eye with 0.0, 0.5 or 1.0 log unit attenuation did not change refractive development. However, monocularly or binocularly attached filters with 2 log units attenuation produced 5-7 D of myopia relative to normal eyes. Black occluders were not more effective. Frosted eye occluders with little effect on image brightness (about 0.5 log units attenuation) produced much more myopia (about 16 D compared with the controls). (2) The effects of the ND filters on refractive development could not be reproduced if the ambient illumination was reduced by 2 log units. Probably, minor effects on image quality were introduced by optical imperfections of the ND filters which were more critical at low retinal image brightness. (3) In an optomotor experiment (spatial frequency 0.2 cyc deg-1, stripe speed 57 deg sec-1), it was shown that the chickens' contrast sensitivity was severely reduced when the eyes were covered by 2.0 ND filters. (4) Since there is evidence that changes in dopamine release from the retina may be one of the factors affecting the development of myopia, we have tested how selective these changes were for spatial information. It was found that dopamine release was controlled by both spatial and luminance information and that the inputs of both could be scarcely separated. (5) Because the experiments show that the eye becomes more sensitive to image degradation at low light, the human eye may also be more prone to develop myopia if the light levels are low during extended periods of near work.

Animals↗
PubMed1996

Inward and outward permeability of the blood-retinal barrier in experimental myopia.

BACKGROUND: To investigate the pathophysiology of the retina in myopia, vitreous fluorophotometry was used to evaluate the permeability of the blood-retinal barrier (BRB) in experimentally induced myopia in cynomolgus monkeys. METHODS: Five animals underwent unilateral eyelid suturing. The suture was removed temporarily at 3, 10, 16, 28 and 36 months, and the dioptric power and axial length were measured in both eyes. Vitreous fluorophotometry was performed before and 60 min after intravenous injection of fluorescein-Na. BRB inward permeability (P(in)) was determined by a computer simulation method. At 36 months, fluorescein-Na was injected into the vitreous cavity, and the intraocular fluorescence was measured. BRB outward permeability (P(out)) was determined by the computer simulation method. RESULTS: Significant myopia developed by 10 months after suturing and progressed thereafter. Starting at 10 months, the P(in) of sutured eyes increased significantly compared with control fellow eyes, and the increase continued throughout the observation period. At 36 months, the BRB P(out) was significantly lower (P < 0.05) in the myopic than in the emmetropic fellow eyes, suggesting decreased active transport mechanisms at the BRB in myopia. CONCLUSION: Our study demonstrated, for the first time, abnormal permeability of the BRB in myopic monkey eyes. Such abnormal permeability may play an important role in the development in human myopes of retinal and vitreous changes such as retinal detachment. Thus, simply correcting refractive errors surgically may not represent a cure for myopia. Patients who have had refractive surgery to correct myopia should also be closely followed up by vitreo-retinal specialists to manage vitreo-retinal disorders in originally myopic eyes.

Animals↗
PubMed2005

A genetic perspective on myopia.

Myopia is a refractive error of the eye that has a significant socioeconomic impact due to its increasing prevalence and the fact that it causes visual impairment. Its aetiology is complex and is likely to involve the interaction of environmental and genetic influences. Tight environmental influence is exemplified by defocus-induced myopia produced in animal models, while genetic factors predominate in familial occurrence of myopia with a Mendelian inheritance pattern. The involvement of numerous mediators, such as cytokines, neurotransmitters and transcription factors, in myopia development has been indicated through various lines of investigation, particular interest focussing on scleral extracellular matrix proteins and developmental genes of the eye. As high-throughput technology for large-scale genotyping and RNA expression analysis enters the field of myopia research, a productive avenue will open up for deciphering the aetiological heterogeneity of myopia and the biological pathways underlying its development.

Animals↗
PubMed1997

[Laser in situ keratomileusis (LASIK) for correction of myopia].

BACKGROUND: Laser in situ keratomileusis (LASIK) preserves the corneal epithelium and Bowman's layer, which theoretically minimizes corneal scarring. We, therefore, evaluated the accuracy, stability and safety of LASIK in moderate to high myopia. PATIENTS AND METHODS: Eighty-five eyes (50 patients) treated using the Automatic Corneal Shaper and the Keracor 116 excimer laser were followed up for 1, 6, and 12 months. Spectacle refraction, visual acuity and rate of retreatments were evaluated. RESULTS: At 12 months, results were as follows: Myopia -5 to -9.9 D (n = 20); 85% within 1 D; regression between one and 12 months < or = 1 D in 90%; uncorrected acuity 20/40 or better in 75%; no loss of two or more lines of visual acuity. Myopia -10 to -14.9 D (n = 33): 73% within 1 D; regression between 1 and 12 months < or = 1 D in 91%; uncorrected acuity 20/40 or better in 79%; 6.1% lost two lines of visual acuity. Myopia -15 to -29 D (n = 32): 31% within 1 D; regression between one and 12 months < or = 1 D in 63%; 6.3% lost two or more lines of visual acuity. Reoperations were performed in two eyes (2.4%) due to epithelial ingrowth or folds of the flap, and in four eyes (4.7%) because of undercorrections or "central islands". CONCLUSIONS: LASIK is an accurate and stable procedure for correcting myopia of -5 to -15 D. In higher myopia, however, results are not satisfactory.

Adult↗
PubMed2004

Reduction of retinal blood flow in high myopia.

PURPOSE: To investigate changes in retinal vessel diameter and blood velocity in high myopia using laser Doppler velocimetry. METHODS: Thirty-nine subjects (39 eyes) were enrolled in the study. The subjects were divided into three groups according to their refractive status; 15 eyes (15 patients) with emmetropia (within +/-3.0 diopters), 14 eyes (14 patients) with mild myopia (between -3.0 and -8.0 diopters), and 10 eyes (10 patients) with high myopia (>-8.0 diopters). Patient age was matched between groups. Blood velocity and vessel diameter of the upper or lower temporal retinal artery were measured using laser Doppler velocimetry with an eye-tracking system, and measurements were compared between groups. RESULTS: The average retinal blood flow and vessel diameter in highly myopic eyes were significantly decreased compared with emmetropic eyes or mild myopic eyes (Mann-Whitney U test, p<0.05). Also, there was significant difference regarding retinal blood flow and vessel diameter between eyes with mild myopia and the other groups. In addition, there was no significant difference in blood velocity between the three groups. CONCLUSIONS: Retinal blood flow was decreased in high myopia, mainly due to the narrowing of the retinal vessel diameter. Impaired retinal blood flow might have a role in the development of chorioretinal atrophy in high myopia.

Adult↗