High-altitude retinopathy and retinal vascular dysregulation

(a) To show that high-altitude retinopathy (HAR) is common at high altitudes even in well-acclimatised climbers and that it should not be regarded as part of the spectrum of benign mountain sickness but rather as a clinical sign with a separate aetiology. (b) To test the hypothesis that HAR could be interpreted as a clinical expression of 'ocular vascular dysregulation'.

Both eyes of the 8 mountaineers of the First Vienna Himalayan Expedition in May/June 1996 were examined 2 weeks before departure to and 2 weeks after descent from a high altitude. Retinal blood flow was measured in the right eyes of 7 climbers, using the Heidelberg Retina Flowmeter (HRF).

Two of the 8 climbers had bilateral retinal haemorrhage after the expedition. In 5 climbers chronic hypoxic exposure caused an increase in retinal blood flow between +18% and +96%, and in 2 climbers a decrease in retinal blood flow between -21% and -31%. The 2 climbers (climbers 1 and 2) with bilateral retinal haemorrhage showed a significant increase in HRF parameters.

HAR may be a clinical sign of mountaineers with a tendency towards ocular vascular dysregulation. The pronounced increase in all haemodynamic parameters in the 2 climbers with retinal haemorrhage combined with a dilated epipapillary network 2 weeks after the exposure reflects a retinal vessel configuration, as might be expected at high altitudes under acute hypoxic stress. An inadequate autoregulatory response of the retinal circulation under conditions of chronic hypoxia may play an important part in the pathogenesis of HAR.