High-altitude pulmonary edema (HAPO) is an acute medical emergency occurring typically in lowlanders, who ascend rapidly to heights of 3000 m or more. It presents with marked dyspnea on exertion, fatigue with minimal-to-moderate effort, prolonged recovery time, and dry cough with manifestations of cyanosis, tachycardia, tachypnea, and temperature which generally does not increase beyond 38.5°C. The condition may be fatal if not treated in time with supplemental oxygen or hyperbaric oxygen or rapid descent to lower altitude. There is paucity in literature on changes in corneal thickness in HAPO. The effect of continued oxygen therapy on corneal thickness has also not been studied in detail. Hence, this study was conducted at high altitude among physician-confirmed HAPO cases. A case-control study was conducted at an altitude of 11,400 feet. Cases were patients suffering from HAPO and controls were patients admitted in hospital for low back pain, fractures, and minor surgical procedures. Central corneal thickness (CCT) was measured with an ultrasound pachymeter on day 1 of hospitalization and every day of hospital stay. Systemic oxygen concentration was also measured daily. There was no statistically significant difference in corneal thickness between two groups at the onset of illness, but a significant decrease in CCT was found in both right and left eyes in HAPO cases when oxygen levels were increased by giving supplemental oxygen. Hierarchical modeling showed a decrease in 1.3 μm in CCT with one unit increase in oxygen mmHg in cases. The findings of statistically insignificant difference in CCT between HAPO cases and controls and a decrease in CCT in HAPO cases on being treated with systemic oxygenation are points to ponder about.

Patyal, Yadav, Kotwal (2018). Changes in corneal thickness in patients with high-altitude pulmonary edema after systemic oxygen therapy. Indian journal of ophthalmology, 2018 Nov;66(11):1554-1557. https://www.ncbi.nlm.nih.gov/pubmed/30355859