High altitude retinal hemorrhages--an update

High altitude retinopathy: An overview and new insights

High altitude retinopathy (HAR) is a common ocular disorder that occurs on ascent to high altitude. There are many clinical symptoms, retinal vascular dilatation, retinal edema and hemorrhage are common. These usually do not or slightly affect vision; rarely, severe cases develop serious or permanent vision loss. At present, the research progress of HAR mainly focuses on hemodynamic changes, blood-retinal barrier damage, oxidative stress and inflammatory response. Although the related studies on HAR are limited, it shows that HAR still belongs to hypoxia, and hypobaric hypoxia plays an aggravating role in promoting the development of the disease. Various studies have demonstrated the correlation of HAR with acute mountain sickness (AMS) and high-altitude cerebral edema (HACE), so a deeper understanding of HAR is important. The slow ascent rates and ascent altitude are the key to preventing any altitude sickness. Research on traditional chinese medicine (TCM) and western medicine has been gradually carried out. Further exploration of the pathogenesis and prevention strategies of HAR will provide better guidance for doctors and high-altitude travelers.

Wilderness Medical Society Clinical Practice Guidelines for Treatment of Eye Injuries and Illnesses in the Wilderness: 2024 Update

A panel convened to develop an evidence-based set of guidelines for the recognition and treatment of eye injuries and illnesses that may occur in the wilderness. These guidelines are meant to serve as a tool to help wilderness providers accurately identify and subsequently treat or evacuate for a variety of ophthalmologic complaints. Recommendations are graded based on the quality of their supporting evidence and the balance between risks and benefits according to criteria developed by the American College of Chest Physicians.

Retinal Manifestations in High Altitude

Dangi, Meenu, Arnab Sadhukhan, Poninder Kumar, S. Bandopadhayay, Vijay K. Sharma, V.K. Patra, Manu Chaudhary, and Vipin Rana. Retinal manifestations in high altitude. High Alt Med Biol. 24:296-301, 2023. Aim: To study the high altitude (HA)-related retinal manifestations among security personnel and thus to provide new insights into the characteristics and mechanisms of retinopathy. Materials and Methods: This was a multicentric, nonrandomized prospective observational and descriptive study. We studied 54 security personnel over 1 year, who were referred from HA areas of northern India and north-eastern India for ocular problems. Complete coagulation profile was performed among patients with vascular occlusion. Results: There were total of 54 patients with ages ranging from 22 to 55 years. HA retinopathy was noticed in 28 patients: central retinal vein occlusion (6 patients), branch retinal vein occlusion (4 patients), branch retinal artery occlusion (1 patient), central retinal artery occlusion (4 patients), ocular ischemic syndrome (1 patient), central serous chorioretinopathy (7 patients), acetazolamide-induced maculopathy (1 patient), and solar retinopathy (2 patients). Along with an increased hematocrit, serum homocysteine was raised in the majority of vascular occlusions. The mean age was 38.16 years, the mean altitude was 14,716 ft, and the mean duration of stay was 11.2 weeks. Conclusion: Hypobaric hypoxia due to HA is a potential risk for HA retinopathy and associated vascular occlusions. Aside from increased hematocrit, hyperhomocysteinemia is a potential cause of vascular occlusions.

Direct ophthalmoscopy as a screening tool to study retinal vascular changes in acute mountain sickness in response to recent ascent to high altitude: A pilot study

Background Advanced diagnostics are not easily accessible in austere topographical locations. We documented retinal changes in patients with acute mountain sickness (AMS+) and compared these with asymptomatic individuals (AMS-) with recent induction into high altitude using direct ophthalmoscopy as a screening tool. Methods We evaluated 97 individuals (43 AMS- and 54 AMS+) who were inducted to an altitude 3800 m above sea level by direct ophthalmoscopy after pupillary dilatation, on day 2 of arrival. Results Retinal vein dilatation was seen in 36 (66.7%) AMS+ v. 14 (32.6%) AMS- (p<0.01), hyperaemia of the optic disc in 30 (55.6%) AMS+ v. 14 (32.6%) AMS- (p<0.05), hyperaemia of the optic disc along with retinal vein dilatation in 27 (50%) AMS+ v. 9 (20.9%) AMS- (p<0.01), retinal vein tortuosity in 12 (22.2%) AMS+ v. 3 (7%) AMS- (p<0.02). In AMS+ with retinal vein dilatation 17 (50%) had SpO2 >91% and 19 (79.2%) had SpO2 <91% (p<0.01). An AMS score of >5 was recorded in 25 (69.4%; p<0.001) with venular dilatation and in 19 (52.8%; p<0.001) who were AMS+ with an induction number ≥3 had retinal dilatation. Conclusion Acute hypobaric hypoxia causes retinal venous dilatation, tortuosity and hyperaemia of the optic disc in those with AMS and correlates directly with SpO2 levels. The incidence of retinal vein dilatation increases with frequent re-entry into high altitude and more severe symptoms of AMS. Hence, all those being inducted to high altitude should be screened for retinal vascular changes.

Proteomic and Morphological Profiling of Mice Ocular Tissue During High-altitude Acclimatization Process: An Animal Study at Lhasa

Purpose

High-altitude environment mainly with hypobaric hypoxia could induce pathological alterations in ocular tissue. Previous studies have mostly focused on sporadic case reports and simulated high-altitude hypoxia experiments. This aim of this study was to explore the proteomic and morphological changes of ocular tissue in mice at real altitude environment.

Methods

In this study, mice were flown from Chengdu (elevation: 500 m) to Lhasa (elevation: 3600 m). After exposure for 1day, 3, 6, 10, 20, 30, and 40days, the mice were euthanatized to obtain blood and ocular tissue. Serological tests, ocular pathological examinations, integral ocular proteomics analysis, and Western blot were conducted.

Results

We focused on acute phase (1–3 days) and chronic phase (>30 days) during high-altitude acclimatization. Serum interleukin-1 was increased at 3 days, while superoxide dismutase, interleukin-6, and tumor necrosis factor-α showed no statistical changes. H&E staining demonstrated that the cornea was edematous at 3 days and exhibited slower proliferation at 30 days. The choroid showed a consistently significant thickening, while there existed no noticeable changes in retinal thickness. Overall, 4073 proteins were identified, among which 71 and 119 proteins were detected to have significant difference at 3 days and 40 days when compared with the control group. Functional enrichment analysis found the differentiated proteins at 3 days exposure functionally related with response to radiation, dephosphorylation, negative regulation of cell adhesion, and erythrocyte homeostasis. Moreover, the differential profiles of the proteins at 40 days exposure exhibited changes of regulation of complement activation, regulation of protein activation cascade, regulation of humoral immune response, second-messenger-mediated signaling, regulation of leukocyte activation, and cellular iron homeostasis. Interestingly, we found the ocular proteins with lactylation modification were increased along high-altitude adaptation.

Conclusion

This is the first work reporting the ocular proteomic and morphological changes at real high-altitude environment. We expect it would deep the understanding of ocular response during altitude acclimatization.

Contributions to Progress in Ophthalmology from Switzerland: From the 16th to the 21st Century

There are numerous contributions to the development of ophthalmology from Switzerland, a country that holds a very special place in the history of medicine from the age of Paracelsus and Vesal to the current time. This review gives an overview over these contributions and the pioneers, among them Johann Friedrich Horner, Hans Goldmann, Jules Gonin, and Walter Rudolf Hess, one of only two ophthalmologists ever awarded the Nobel Prize for Medicine. A leading role in this evolution of modern ophthalmology has been played by physicians from Basel, home of Switzerland's oldest university.

Systemic hypoxia led to little retinal neuronal loss and dramatic optic nerve glial response

Vision loss is a devastating consequence of systemic hypoxia, but the cellular mechanisms are unclear. We investigated the impact of acute hypoxia in the retina and optic nerve. We induced systemic hypoxia (10% O₂) in 6-8w mice for 48 h and performed in vivo imaging using optical coherence tomography (OCT) at baseline and after 48 h to analyze structural changes in the retina and optic nerve. We analyzed glial cellular and molecular changes by histology and immunofluorescence and the impact of pretreatment with 4-phenylbutyric acid (4-PBA) in oligodendroglia survival. After 48 h hypoxia, we found no change in ganglion cell complex thickness and no loss of retinal ganglion cells. Despite this, there was significantly increased expression of CCAAT-enhancer-binding protein homologous protein (CHOP), a marker of endoplasmic reticulum stress, in the retina and optic nerve. In addition, hypoxia induced obvious increase of GFAP expression in the anterior optic nerve, where it co-localized with CHOP, and significant loss of Olig2⁺ oligodendrocytes. Pretreatment with 4-PBA, which has been shown to reduce endoplasmic reticulum stress, rescued total Olig2⁺ oligodendrocytes and increased the pool of mature (CC-1⁺) but not of immature (PDGFRa+) oligodendrocytes. Consistent with a selective vulnerability of the retina and optic nerve in hypoxia, the most striking changes in the 48 h murine model of hypoxia were in glial cells in the optic nerve, including increased CHOP expression in the astrocytes and loss of oligodendrocytes. Our data support a model where glial dysfunction is among the earliest events in systemic hypoxia - suggesting that glia may be a novel target in treatment of hypoxia.

In vivo monitoring the dynamic process of acute retinal hemorrhage and repair in zebrafish with spectral-domain optical coherence tomography

Retina, the only light sensor in the human eye, is hidden and extremely fragile. Optimized animal models and efficient imaging techniques are very important for the study of retinopathy. In this work, the rapid retinal injury process and the long-term retinal repair process were in vivo continuously evaluated with a novel imaging technology spectral-domain optical coherence tomography (SD-OCT) in a unique animal model zebrafish. Acute retinal injury was constructed on adult zebrafish by needle injection surgery. SD-OCT imaging was carried out immediately after the mechanical injury. The retinal hemorrhage, which lasted only 5 seconds, could be visualized dynamically by SD-OCT. The process of blood clearance and retinal repair was also evaluated because SD-OCT imaging is nondestructive. Both SD-OCT imaging results and behavioral analyzing results demonstrated that zebrafish retina could be repaired by itself within 15 days, which was confirmed by the results of pathological experiment.

Wilderness Medical Society Clinical Practice Guidelines for Diabetes Management

The Wilderness Medical Society convened an expert panel in 2018 to develop a set of evidence-based guidelines for the treatment of type 1 and 2 diabetes, as well as the recognition, prevention, and treatment of complications of diabetes in wilderness athletes. We present a review of the classifications, pathophysiology, and evidence-based guidelines for planning and preventive measures, as well as best practice recommendations for both routine and urgent therapeutic management of diabetes and glycemic complications. These recommendations are graded based on the quality of supporting evidence and balance between the benefits and risks or burdens for each recommendation.

Mountain neurology

Mountain climbers may develop specific illnesses that largely depend on the altitude reached and the rate of ascent. The popularity of travel to high altitude destinations, extreme tourist activities and mountain climbing means that neurologists in low-altitude countries are increasingly likely to encounter neurological problems and disorders in people exposed to high altitude. Additionally, they may have to advise patients with pre-existing neurological conditions on the risks of ascent to altitude. This article focuses on neurological-related high-altitude illnesses: acute mountain sickness and high-altitude cerebral oedema, as well as high-altitude retinopathy and other neurological disorders. This overview combines current understood pathogenesis with the experience of managing altitude-related illness at the foot of Mount Kilimanjaro in northern Tanzania, the tallest free-standing mountain in the world.

Practical Tips for Working as an Expedition Doctor on High-Altitude Expeditions

Brants, Anne, and Tracee Metcalfe. Practical tips for working as an expedition doctor on high-altitude expeditions. High Alt Med Biol. 18:193-198, 2017.-With the explosion of adventure travel over the past decade, there has been a concurrent increase in mountaineering expeditions to extreme elevations, including many of the 8000-m peaks. This trend has created an increased demand for qualified expedition doctors to provide specialized medical advice and care to climbers and expedition staff. This review is intended to help physicians prepare for work on such expeditions. The authors rely heavily on their own experience and discuss the types of work available on high-altitude expeditions; how to identify a safe and reputable guiding company; personal and medical preparation; priorities in selecting or building an appropriate medical kit; and medical conditions commonly encountered on expeditions. The review concludes by considering ethical dilemmas and other difficult issues unique to this work.

Retinal venous pressure: the role of endothelin

The retinal venous pressure (RVP) can be measured non-invasively. While RVP is equal to or slightly above intraocular pressure (IOP) in healthy people, it is often markedly increased in patients with eye or systemic diseases. Beside a mechanical obstruction, the main cause of such an elevation is a local dysregulation of a retinal vein, particularly a constriction induced by endothelin-1 (ET-1). A local increase of ET-1 can result from a high plasma level, as ET-1 can diffuse from the fenestrated capillaries of the choroid into the optic nerve head (ONH), bypassing the blood retinal barrier. A local increase can also result from increased local production either by a sick neighboring artery or retinal tissue. Generally, the main factors increasing ET-1 are inflammations and hypoxia, either locally or in a remote organ. RVP is known to be increased in patients with glaucoma, retinal vein occlusion (RVO), diabetic retinopathy, high mountain disease, and primary vascular dysregulation (PVD). PVD is the major vascular component of Flammer syndrome (FS). An increase of RVP decreases perfusion pressure, which heightens the risk for hypoxia. An increase of RVP also elevates transmural pressure, which in turn heightens the risk for retinal edema. In patients with RVO, a high level of RVP may not only be a consequence but also a potential cause of the occlusion; therefore, it risks causing a vicious circle. Narrow retinal arteries and particularly dilated retinal veins are known risk indicators for future cardiovascular events. As the major cause for such a retinal venous dilatation is an increased RVP, RVP may likely turn out to be an even stronger predictor.

Circadian rhythm of peripheral perfusion during 10-day hypoxic confinement and bed rest

INTRODUCTION

Future planetary habitats will be hypobaric and hypoxic to reduce the risk of decompression sickness during preparation for extra-vehicular activities. This study was part of a research programme investigating the combined effects of hypoxia and microgravity on physiological systems.

PURPOSE

We tested the hypothesis that hypoxia-induced peripheral vasoconstriction persists at night and is aggravated by bed rest. Since sleep onset has been causally linked to nocturnal vasodilatation, we reasoned that hypoxia-induced vasoconstriction at night may explain sleep disturbances at altitude. Peripheral perfusion alterations as a consequence of bed rest may explain poor sleep quality reported during sojourns on the International Space Station.

METHODS

Eleven males underwent three 10-day interventions in a randomised order: (1) hypoxic ambulatory confinement; (2) hypoxic bed rest; (3) normoxic bed rest. During each intervention we conducted 22-h monitoring of peripheral perfusion, as reflected by the skin temperature gradient. Measurements were conducted on the first (D 1) and last day (D 10) of each intervention.

RESULTS

All interventions resulted in a decrease in daytime toe perfusion from D 1 to D 10. There was no difference in the magnitude of the daytime reduction in toe perfusion between the three interventions. There was a significant vasodilatation of the toes in all interventions by 11 pm. The fingertips remained well perfused throughout.

CONCLUSIONS

Daytime vasoconstriction induced by hypoxia and/or bed rest is abolished at night, lending further support to the theory that changes in peripheral skin temperature may be functionally linked to sleep onset.