RESUMEN
PURPOSE: The Ishihara pseudoisochromatic (PIC) plate test is the most used test for identifying red-green colour-deficient individuals, but it is not known how the Ishihara results compare with that of genetics testing. Here, the outcome of genotype analysis of OPN1LW and OPN1MW was compared with that of the Ishihara (24-plate ed., 1964) and the Hardy-Rand-Rittler (4th ed. 2002) PIC plate tests. METHODS: Healthy participants with normal habitual visual acuity (n = 454, 16-24 years; 193 males; logMAR ≤ 0.00) gave saliva samples for opsin gene analysis and performed the two PIC plate tests as part of a cross-sectional study. The criteria for failing the PIC tests were according to manufacturers' instructions. DNA was extracted and used in genotyping assays of OPN1LW and OPN1MW genes from each participant using the Agena MassArray genotyping system. RESULTS: Ten male (5.2%) and 3 (1.1%) female participants were identified as red-green colour deficient based on PIC tests alone. The combination of MassArray and PIC test results identified 10.4% of male and 0.8% of female participants to be colour deficient (males: 0.5% protan and 9.9% deutan; females: 0.8% deutan). Hardy-Weinberg calculations based on male frequencies from combining the MassArray and the PIC test results gave female frequency estimates of colour deficiency and carriers closely matching measured frequencies. CONCLUSIONS: MassArray identified twice as many colour-deficient males as identified from PIC tests alone. Combining results from MassArray and the PIC tests proves to be more reliable than any single test at correctly identifying red-green colour-deficient individuals and carriers.
Asunto(s)
Defectos de la Visión Cromática , Pruebas de Percepción de Colores/métodos , Defectos de la Visión Cromática/diagnóstico , Defectos de la Visión Cromática/genética , Estudios Transversales , ADN , Femenino , Pruebas Genéticas , Humanos , Masculino , OpsinasRESUMEN
In syndromic forms of myopia caused by long (L) to middle (M) wavelength (L/M) interchange mutations, erroneous contrast signals from ON-bipolar cells activated by cones with different levels of opsin expression are suggested to make the eye susceptible to increased growth. This susceptibility is modulated by the L:M cone ratio. Here, we examined L and M opsin genes, L:M cone ratios and their association with common refractive errors in a population with low myopia prevalence. Cycloplegic autorefraction and ocular biometry were obtained for Norwegian genetically-confirmed normal trichromats. L:M cone ratios were estimated from spectral sensitivity functions measured with full-field ERG, after adjusting for individual differences in the wavelength of peak absorption deduced from cone opsin genetics. Mean L:M cone ratios and the frequency of alanine at L opsin position 180 were higher in males than what has been reported in males in populations with high myopia prevalence. High L:M cone ratios in females were associated with lower degree of myopia, and myopia was more frequent in females who were heterozygous for L opsin exon 3 haplotypes than in those who were homozygous. The results suggest that the L:M cone ratio, combined with milder versions of L opsin gene polymorphisms, may play a role in common myopia. This may in part explain the low myopia prevalence in Norwegian adolescents and why myopia prevalence was higher in females who were heterozygous for the L opsin exon 3 haplotype, since females are twice as likely to have genetic polymorphisms carried on the X-chromosome.
Asunto(s)
Opsinas de los Conos/genética , Predisposición Genética a la Enfermedad , Miopía/genética , Células Fotorreceptoras Retinianas Conos/patología , Adolescente , Biometría , Visión de Colores/fisiología , Electrorretinografía , Femenino , Humanos , Masculino , Noruega , Reacción en Cadena de la Polimerasa , Polimorfismo de Nucleótido Simple , Refracción Ocular/fisiología , Retina/fisiopatología , Adulto JovenRESUMEN
East Asia has experienced an excessive increase in myopia in the past decades with more than 80% of the younger generation now affected. Environmental and genetic factors are both assumed to contribute in the development of refractive errors, but the etiology is unknown. The environmental factor argued to be of greatest importance in preventing myopia is high levels of daylight exposure. If true, myopia prevalence would be higher in adolescents living in high latitude countries with fewer daylight hours in the autumn-winter. We examined the prevalence of refractive errors in a representative sample of 16-19-year-old Norwegian Caucasians (n = 393, 41.2% males) in a representative region of Norway (60° latitude North). At this latitude, autumn-winter is 50 days longer than summer. Using gold-standard methods of cycloplegic autorefraction and ocular biometry, the overall prevalence of myopia [spherical equivalent refraction (SER) ≤-0.50 D] was 13%, considerably lower than in East Asians. Hyperopia (SER ≥ + 0.50 D), astigmatism (≥1.00 DC) and anisometropia (≥1.00 D) were found in 57%, 9% and 4%. Norwegian adolescents seem to defy the world-wide trend of increasing myopia. This suggests that there is a need to explore why daylight exposure during a relatively short summer outweighs that of the longer autumn-winter.