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

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.

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.

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.

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.

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.