Are High Altitude Environments Dangerous to the Optic Disc?

There were significant delays between the onset of visual symptoms and high-altitude exposure: two patients developed symptoms one week after leaving Tibet, following a one-month stay there. For the same reason, the researchers also believed that there was no direct relationship between hypoxia and optic disc swelling in our cohort. These images from the paper show fundus photos taken at 25 days (A, B) and visual field evolution in the right eye (A, C, E, G) and left eye (B, D, F, H) at 10 days (C, D), 50 days (E, F) and 70 days (G H) after disease onset, respectively. Photo: Li Y, et al. BMC Ophthalmol. 2025;25(1):242. Click image to enlarge. Sporadic cases of optic disc edema accompanied by decreased visual function have been reported in people exposed to a high altitude environment, such as from mountain climbing. Most of these cases were diagnosed as monocular nonarteritic anterior ischemic optic neuropathy (NAION). A small cup-to-disc ratio or small optic discs (also referred to as congenitally anomalous discs or “discs at risk”) is the strongest risk factor associated with NAION. Researchers in China recently assessed six patients with optic disc edema and decreased visual function following a tour on the Tibetan plateau. Five patients exhibited binocular involvement, while one case was monocular. The study determined that the one case with monocular involvement had a cup-to-disc ratio of 0.1 in the contralateral eye, which could be diagnosed as NAION. The team then hypothesized that both monocular and binocular NAION can occur after high-altitude exposure.This retrospective analysis included 11 eyes of six patients (five men and one woman), with a mean age of 47.3 years. Clinical characteristics, intracranial pressure, 24-hour ambulatory blood pressure and polysomnography data were retrospectively collected from patients presenting with optic disc edema and decreased visual function after high-altitude exposure on the Tibetan plateau between October 2020 and September 2023.All cases presented with diffuse disc edema at onset, which gradually resolved within eight weeks. There was a definite time lag, ranging from seven days to one month, between arrival at high altitude and symptom onset. All patients had normal intracranial pressure. Mean visual acuity was worst (20/50) at two weeks, and the best mean visual acuity was 20/30 at six months. Visual field defects were observed in all patients at the early stage of the disease, with some residual defects remaining. One patient had a small cup-to-disc ratio in the contralateral eye, while the other five could not be assessed due to bilateral optic disc edema. One patient had hypertension and severe sleep apnea, one had hypercholesterolemia and hypertension and one had hypercholesterolemia alone.Because NAION due to high-altitude exposure has not been adequately explored, the researchers offered some possible causes in their paper, which was published in BMC Ophthalmology. Vigorous physical exercise during excursions at high altitude, combined with hypoxia during sleep, may contribute to reduced oxygen supply to the optic nerve head, they proposed. Other possible factors include higher altitude, faster ascent, longer duration at high altitude, lower hematocrit levels,, strenuous activity and higher baseline intraocular pressure.“Upon returning to normal altitude, pathophysiological changes from hypoxia can have a significantly harmful impact on the terminal blood vessels—the short posterior ciliary arteries. This may result in ischemia of the short posterior ciliary arteries, leading to NAION,” the researchers hypothesized in their paper. “This pathogenesis also explains why diffuse visual field defects are more commonly observed than inferior altitudinal losses.” Nevertheless, research on this mechanism of optic disc edema associated with high altitude has only focused on the early stages of high-altitude exposure, with little understanding of ocular symptoms and signs. Why many patients developed symptoms after leaving high altitude rather than during high-altitude exposure requires further research. Click here for the journal source.  Li Y, Sun M, Chen B, et al. Optic disc edema with decreased visual function after high-altitude exposure. BMC Ophthalmol. 2025;25(1):242.