Determination of Color Vision in School Children in High Altitude, Leh, India.

UNLABELLED: Patyal, Sagarika, Jasdeep Singh, Kanika Bhardwaj, and Uday Yanamandra. Determination of color vision in school children in high altitude, Leh, India. High Alt Med Biol. 00:00-00, 2026. INTRODUCTION: Color vision deficiency (CVD) is a heritable condition predominantly affecting males due to its X-linked recessive inheritance. High altitude may exacerbate color discrimination impairment through hypobaric hypoxia-mediated depression of retinal function, particularly affecting short-wavelength cone pathways. Population-based data on CVD from high-altitude Indian communities are absent from the literature. MATERIALS AND METHODS: A cross-sectional study was conducted at Lamdon School, Leh, Ladakh, India (11,400 ft/3,474 m above sea level). A total of 505 schoolchildren (204 boys; 301 girls) aged 11-18 years underwent a structured ophthalmical examination and color vision testing using the 38-plate Ishihara pseudoisochromatic plate test under standardized conditions. RESULTS: CVD was detected in 53 of 505 children (10.50%): 22 boys (10.78%) and 31 girls (10.30%). No statistically significant sex difference in CVD prevalence was detected (Fisher's exact test, p = 0.883). Severity analysis revealed a significant sex interaction: girls predominated in mild (21/33) and moderate (9/12) CVD categories, while boys constituted 7 of 8 severely color-deficient children (≥5 plate errors). CVD prevalence rose with age, peaking at 20.7% in 18-year-olds. Plates 9 and 17 generated the highest error frequencies; plate 9 elicited errors exclusively in boys, and plate 17 elicited errors exclusively in girls. Plate-specific misidentification patterns deviated from standard Ishihara predictions in both sexes. CONCLUSIONS: The overall CVD prevalence in this high-altitude Ladakhi population substantially exceeds rates reported at sea level in India and most global populations, mirroring the altitude-related pattern documented in Nepal. The severity paradox, girls dominating mild CVD while boys dominate severe CVD, suggests that carrier females heterozygous for CVD-associated alleles may be expressing phenotypically detectable color discrimination impairment at altitude, possibly through hypoxia-mediated amplification of their marginal trichromatic capacity.