Genetic and environmental effects on the development of myopia in Chinese twin children

In order to assess the relative and interactive importance of genetic and environmental components on the development of myopia in Chinese school children aged from 10 to 15 years, a population-based sample of 361 same-sexed twin pairs recruited through stratified cluster sampling was studied. Zygosity of twin pairs was determined by Mendelian traits, red cell antigen systems, and continuous dermatoglyphic characteristics; while myopia was diagnosed by both objective and subjective techniques. Studying and reading habit was obtained from cotwins and their parents through a life style questionnaire. Age-sex-adjusted concordance rate derived from multiple regression equation was used in the analysis. Conventional comparison of intrapair concordance between monozygotic (MZ) and dizygotic (DZ) twins was used to assess the importance of a genetic component in the determining of myopia, and a significant genetic influence was observed. Environmental influence on myopia was evaluated through MZ cotwin method, and MZ cotwins with concordant studying and reading habits were significantly more concordant in myopia than those MZ cotwins with discordant habits. The possible effect of gene-environment interaction on myopia was explored, and concordance in myopia was found significantly associated with the interaction between zygosity and habit of studying and reading. These observations suggested that the impact of the environmental factor on the development of myopia may be influenced by genotype, and vice versa.

Autosomal dominant cataract and microcornea associated with myopia in a Sicilian family

A Sicilian family is reported in which 36 individuals, in 5 successive generations, were affected with congenital cataracts, microcornea and myopia with an autosomal pattern of inheritance.

Prevalence of myopia in school children in Vanuatu

The onset of myopia typically occurs in childhood and increases during puberty. We studied the vision and refractive errors of 977 school children (ages 6 to 17 years) in 1983. Myopia in the group was extremely low; 97% had vision of 6/6, and 1.3% had myopia greater than 0.25D. Regression analysis revealed a change in mean refraction of -0.016D/year for males and -0.024D/year for females. There were no significant differences between males and females. These children engaged in about 8 hours of school work per day, and we conclude that genetic factors predominate over environmental factors in the determination of myopic refractive errors for this group.

Primary angle closure glaucoma in a myopic kinship

Three related myopic individuals with primary angle closure glaucoma are reported. They had true myopia and not pseudomyopia secondary to increased lenticular index of refraction. We believe one of these individuals (-8.62 spherical equivalent) to have the most myopic case of primary angle closure glaucoma reported in the literature. Although myopia is associated with anatomical factors that offer considerable protection from primary angle closure glaucoma, its presence does not eliminate the possibility of this disease. Laser iridectomy was effective in the treatment of these patients.

Leber's optic atrophy with myopia masquerading as glaucoma: case report

In recent years there has been much discussion in the literature regarding the proper approach to the patient who presents with apparent "low tension" glaucoma. In addition to a complete workup and proper management of such a patient, careful consideration must be given to the differential diagnosis of clinical conditions presenting with optic disc cupping and visual field changes. We present an interesting clinical situation in which a patient with severe myopia and Leber's optic atrophy was referred for surgery for treatment of apparent progressive "low tension" glaucoma.

Segregation analysis of ocular refraction and myopia

Segregation analysis of ocular spherical refraction data using a unified model resulted in rejection of a Mendelian hypothesis of genetic transmission in nuclear families of both Japanese and European ancestries. Similar analyses of families which included at least 1 myope gave no evidence for the hypothesis that myopia is determined in part by a major gene. Most of the variation associated with ocular refraction, or with myopia, seems to be nongenetic in origin.

Cardiovascular findings in congenital contractural arachnodactyly: report of an affected kindred

Three generations of a kindred had a history and physical findings consistent with congenital contractural arachnodactyly (CCA) segregating in an autosomal-dominant manner. Six of the seven affected patients we examined had mitral valve prolapse (MVP) diagnosed clinically or by echocardiography. The family members without CCA did not have MVP. This association of cardiac involvement with CCA further lessens the distinction between CCA and the Marfan syndrome. The indication for ophthamologic and echocardiographic follow-up of patients carrying the diagnosis of CCA is stressed.

Spherophakia in a Newfoundland family: 8 years' experience

In a family with eight siblings, five siblings have had spherophakia. One patient has died, but the other four have been followed up for 8 years. Two have undergone peripheral iridectomy because of steadily rising intraocular pressure. The operations were only partially successful in controlling the pressure. Whether associated with the Weill-Marchesani syndrome or not, spherophakia is difficult to manage. The lenticular myopia must be corrected (sometimes an additional reading correction is needed), and the intraocular pressure and visual field must be carefully monitored. The ability of the retinal circulation to withstand a high intraocular pressure for long periods may not be matched by a corresponding resilience of the drainage mechanism. Therefore, early peripheral iridectomy is probably advisable.

The photopic electroretinogram in congenital stationary night blindness with myopia

Previous studies have reported that subjects affected with congenital stationary night blindness and myopia demonstrated some photopic (cone) abnormalities in their electroretinogram (ERG). By comparing the photopic ERG elicited with a threshold and a suprathreshold stimulus it was found that, at threshold, no significant differences were noted both in the peak time and in the amplitude of ERGs evoked from CSNB and normal subjects. However, a more powerful stimulus (16 times the threshold) yields a significant difference in the ERGs recorded from the two groups. ERGs recorded from CSNB patients are decreased in amplitude with a b-wave peak time that remains normal. First derivative analysis of the ERG wave along with a selective recording of the oscillatory components of the ERG suggest that the only visible anomaly in the suprathreshold photopic ERG of CSNB patients is an absence of the two oscillations normally seen on the ascending portion of the b-wave. Data obtained on normal subjects are also reported that try to explain the functional significance of these two oscillatory potentials.

The Eisdell pedigree. Congenital stationary night-blindness with myopia

A pedigree of X-linked congenital stationary night-blindness, originally published by Nettleship, is presented with abstracts from his private correspondence. An affected descendant has supplied letters and the original working pedigree which led to the publication of the extended pedigree in 1912.

Clinical variability in vitreoretinal degeneration

Three families with a wide range of vitreoretinal degeneration, median cleft face syndrome and skeletal anomalies are described. Their autosomal dominant transmission and phenotypic spectrum are presented. In view of the similarity between these patients and the clinical overlap existing between them, it is assumed that they are all the same entity forming parts of a continuum. As the pleiotropic gene has such different and varying expressivity with regard to the organ system involved, it is presumed that the dominance in this complex disorder is irregular.

Genetic aspects of myopia among the Shia Muslim Dawoodi Bohras of Udaipur, Rajsthan

359 sibs from 92 families, where any one member of the family (basic unit of study) was found to be affected, were screened for myopia. Data on age at onset, parity and severity were studied in relation to consanguinity. Significant consanguinity differentials in the manifestation of myopia were seen. Offspring who were the product of a consanguineous mating manifested myopia more frequently as compared to the offspring from the non-consanguineous matings (control group). Males from consanguineous matings were affected in a higher frequency and manifested myopia at early ages. Myopia was found to be birth order-dependent. Pedigree analysis has shown that myopia is not a monogenic trait. The most plausible mode of inheritance of myopia seems to be polygenic with variable expressivity, and shows gene dosage effect.

Pseudoinflammatory fundus dystrophy with autosomal recessive inheritance

A family in southwest Finland with bilateral hemorrhagic degeneration of the retina and choroid was followed up for more than 16 years. The maculas showed subretinal hemorrhages, glial cicatrization of the outer retinal layers, and profound choroidal atrophy, particularly in the advanced stages of the disease. Fluorescein angiography demonstrated leakage through the pigment layer in the retinal tissue. The age of onset varied from the second to the fourth decade. The clinical pattern was similar to Sorsby's pseudoinflammatory dominant fundus dystrophy, except that the disorder appeared earlier in this Finnish family, the members of which show secondary dyschromatopsia, many deep hyaloid bodies in the retina, disturbed dark adaptation (1 to 4 log units), subnormal light-peak/dark-trough ratios, progressive myopia, and a mode of inheritance which is probably autosomal recessive. The affected parents are consanguineous in many ways and each of their eight children is affected.

Do sex, ethnic origin or environment affect myopia?

The degree of myopia was investigated in males and females from the same ethnic group who were raised in the same environment, in subjects from the same origin who were raised in extremely different environments, and in subjects coming from different ethnic groups. No statistically significant differences were found between these groups. Most probably the degree of myopia is not influenced just by sex or ethnic origin or environmental conditions.

Autosomal recessive vitreoretinopathy and encephaloceles

We conducted a ten-year follow-up of an unusual pedigree with an autosomal recessive vitreoretinal degeneration, severe myopia, and congenital encephalocele. All five affected members (four girls and one boy) also had early, recurrent bilateral detachments. Color vision testing disclosed an acquired tritan dyschromatopsia and electroretinography showed subnormal photopic and scotopic amplitudes, delayed b-wave implicit times and 30-Hz flicker-phase relations, and absent scotopic b-wave oscillations.

Marshall/Stickler syndrome

A family originally reported as a variant of Marshall syndrome is re-examined. The clinical picture now encompasses both the Marshall and Stickler syndromes and it is suggested that the distinction between the two should be abandoned.