Delayed high-altitude retinal hemorrhages in well-acclimatized lowlanders: A hidden risk unveiled.

Background/objectives: High-altitude retinal hemorrhage (HARH), a frequent entity of high-altitude retinopathy (HAR), is associated with acute exposure to high altitudes (HAs) with rapid ascent. However, the delayed occurrence of HARH in well-acclimatized individuals has received less attention. This study explored the prevalence and characteristics of HARH in individuals who were acclimatized to HA for extended periods, aiming to elucidate the physiological responses of the retina to chronic hypoxic conditions.

Subjects/methods: We conducted an observational cross-sectional study involving 1,457 male participants who had resided at altitudes above 3353 meters (11,000 ft) in the Himalayan region for more than three months. Patients who had ocular or systemic diseases affecting the retina, chronic retinotoxic medication use or smoking were excluded. Participants underwent comprehensive ophthalmic examination, including the best corrected visual acuity test, dilated fundus examination and photography.

Results: A total of 1,457 males were screened, and the mean age was 34 ± 2 years. Of all the participants screened, 12 (0.82%) had HAR, with all cases occurring at altitudes above 4267 meters (14,000 ft). Seventy-five percent (75%) of the HAR patients had retinal hemorrhage and venous dilatation. Macular involvement and cotton wool spots were observed in 34% and 25% of HAR patients, respectively. Only four participants had foveal involvement with significant visual impairment.

Conclusion: Delayed HARH in acclimatized individuals underscores the importance of long-term ocular monitoring for those exposed to HA, despite acclimatization, to prevent and manage potential visual impairments.