High Altitude Retinopathy Research Articles

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

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. 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. 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. 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.

Effects of Acute High-Altitude Exposure on Morphology and Function of Retinal Ganglion Cell in Mice.

High altitude retinopathy (HAR) is a retinal functional disorder caused by inadequate adaptation after exposure to high altitude. However, the cellular and molecular mechanisms underlying retinal dysfunction remain elusive. Retinal ganglion cell (RGC) injury is the most important pathological basis for most retinal and optic nerve diseases. Studies focusing on RGC injury after high-altitude exposure (HAE) are scanty. Therefore, the present study sought to explore both functional and morphological alterations of RGCs after HAE. A mouse model of acute hypobaric hypoxia was established by mimicking the conditions of a high altitude of 5000 m. After HAE for 2, 4, 6, 10, 24, and 72hours, the functional and morphological alterations of RGCs were assessed using retinal hematoxylin and eosin (H&E) sections, retinal whole mounts, transmission electron microscopy (TEM), and the photopic negative response (PhNR) of the electroretinogram. Compared with the control group, the thickness of the ganglion cell layer and retinal nerve fiber layer increased significantly, RGC loss remained significant, and the amplitudes of a-wave, b-wave, and PhNR were significantly reduced after HAE. In addition, RGCs and their axons exhibited an abnormal ultrastructure after HAE, including nuclear membrane abnormalities, uneven distribution of chromatin in the nucleus, decreased cytoplasmic electron density, widening and vacuolization of the gap between axons, loosening and disorder of myelin sheath structure, widening of the gap between myelin sheath and axon membrane, decreased axoplasmic density, unclear microtubule and nerve fiber structure, and abnormal mitochondrial structure (mostly swollen, with widened membrane gaps and reduced cristae and vacuolization). The study findings confirm that the morphology and function of RGCs are damaged after HAE. These findings lay the foundation for further study of the specific molecular mechanisms of HAR and promote the effective prevention.

AQP4- and Kir4.1-Mediated Müller Cell Oedema Is Involved in Retinal Injury Induced By Hypobaric Hypoxia.

Hypobaric hypoxia is the main cause of high-altitude retinopathy (HAR). Retinal oedema is the key pathological change in HAR. However, its pathological mechanism is not clear. In this study, a 5000-m hypobaric hypoxic environment was simulated. Haematoxylin and eosin (H&E) staining and electrophysiological (ERG) detection were used to observe the morphological and functional changes in the retina of mice under hypobaric hypoxia for 2-72h. Toluidine blue staining and transmission electron microscopy were used to observe the morphology of Müller cells in the hypobaric hypoxia groups. The functional changes and oedema mechanism of Müller cells were detected by immunofluorescence and western blotting. The expression levels of glutamine synthetase (GS), glial fibrillary acidic protein (GFAP), aquaporin 4 (AQP4), and inwardly rectifying potassium channel subtype 4.1 (Kir4.1) in Müller cells were quantitatively analysed. This study revealed that retinal oedema gradually increased with prolonged exposure to a 5000-m hypobaric hypoxic environment. In addition, the ERG showed that the time delay and amplitude of the a-wave and b-wave decreased. The expression of GS decreased, and the expression of GFAP increased in Müller cells after exposure to hypobaric hypoxia for 4h. At the same time, retinal AQP4 expression increased, and Kir4.1 expression decreased. The oedema and functional changes in Müller cells are consistent with the time point of retinal oedema. In conclusion, Müller cell oedema is involved in retinal oedema induced by hypobaric hypoxia. An increase in AQP4 and a decrease in Kir4.1 are the main causes of Müller cell oedema caused by hypobaric hypoxia.

Population Prevalence, Pattern and Associated Factors for Retinal Diseases at High Altitude in Nepal.

Retinal diseases are common at high altitudes due to a cascade of changes caused by hypoxia. The aim of this study is to assess the population prevalence, pattern and associated factors of retinal disorders at high altitude in Nepal. A cross-sectional study was conducted at three selected high-altitude districts (over 2500 meters) of Nepal. Subjects were at least 40 years old, and the target sample size was 309. A detailed history was taken. Visual acuity, blood sugar, blood pressure, and oxygen saturation were measured. Anterior and posterior ocular evaluations were conducted by retina specialists using slit lamp and indirect ophthalmoscopy. A total of 338 participants were recruited, with nearly equal numbers from the three districts with mean age of 57.0 (S.D 11.1) years. Two-thirds (63.9%) were females; 38.2% were illiterate, and 46.7% were farmers. Average blood oxygen saturation was 87.2% (S.D 4.1%). Systemic hypertension and diabetes mellitus were found in 58% and 11%, respectively. Retinal diseases were found in 176 (52.5%), with bilateral involvement in 157 (46.9%). The major retinal diseases were hypertensive retinopathy (32.2%), high-altitude retinopathy (10.4%), age-related macular degeneration (AMD) (8.1%), branch vein occlusion (BRVO) (2.1%), and diabetic retinopathy (DR) (1.8%). The multivariate analysis showed significant association of retinal diseases with age and hypertension. Best corrected visual acuity better than 6/18 was present in 96.7%. Over half of the study participants had retinal diseases, with hypertensive retinopathy, AMD, and high-altitude retinopathy as the most common retinal problems. A significant association of retinal diseases was found with ageing, and hypertension. Access to eye care services and control of systemic hypertension along with patient education should be emphasized among people living at high-altitude.

Impact of flight and equivalent short-term high-altitude exposure on ocular structures and function.

Exposure to high-altitude conditions during flight or similar activities affects many aspects of visual function, which is critical not only for flight safety but for any altitude-related activity. We aimed to summarize the available literature pertaining to ocular changes during flight or equivalent short-term high-altitude exposure (e.g., hypobaric chamber, effortless ascent lasting ≤ 24 h) and to highlight future research priorities. Using the PubMed/MEDLINE and Web of Science/ISI Web of Knowledge databases with structured search syntax, we conducted a systematic review of the literature spanning a 40-year period (January 1, 1983, to October 10, 2023). Articles pertaining to ocular changes during flight or flight-equivalent exposure to altitude were retrieved. The reference lists of retrieved studies were also searched, and citations of these references were included in the results. Of 875 relevant PubMed and ISI publications, 122 qualified for inclusion and 20 more were retrieved from the reference lists of initially selected records, for a total of 142 articles. Reported anterior segment changes included deterioration in tear film stability and increased dry eye incidence, increased corneal thickness, discomfort and bubble formation in contact lens users, refraction changes in individuals with prior refractive surgery, decreased intraocular pressure, and alterations in pupillary reaction, contrast sensitivity, and visual fields. Photoreceptor-visual pathway changes included alterations in both photoreceptors and neuro-transduction, as evidenced in dark adaptation, macular recovery time, reduction in visual field sensitivity, and optic neuritis (likely an element of decompression sickness). Retinochoroidal changes included increases in retinal vessel caliber, retinal blood flow, and choroidal thickness; central serous chorioretinopathy; and retinal vascular events (non-arteritic ischemic optic neuropathy, high-altitude retinopathy, and retinal vein occlusion). The effect of short-term high-altitude exposure on the eye is, in itself, a difficult area to study. Although serious impairment of visual acuity appears to be rare, ocular changes, including tear film stability, contact lens wear, central corneal thickness, intraocular pressure, contrast sensitivity, stability of refractive surgeries, retinal vessels, visual fields, and macula recovery time, should be considered in civilian aviators. Our report provides guidance to climbers and lowlanders traveling to altitude if they have pre-existing ocular conditions or if they experience visual symptoms while at altitude. However, key outcomes have been contradictory and comprehensive studies are scarce, especially those pertaining to the choroid and retina. Such studies could not only deepen our understanding of high-altitude ocular pathophysiology, but could also offer valuable information and treatment possibilities for a constellation of other vision-threatening diseases.

Retinal Vascular Changes in Response to Hypoxia: A High-Altitude Expedition Study.

Westwood, Jessica, India Mayhook-Walker, Ciaran Simpkins, Andrew Darby-Smith, Dan Morris, and Eduardo Normando. Retinal vascular changes in response to hypoxia: a high-altitude expedition study. High Alt Med Biol. 25:49-59, 2024. Background: Increased tortuosity and engorgement of retinal vasculature are recognized physiological responses to hypoxia. This can lead to high-altitude retinopathy (HAR), but incidence reports are highly variable, and our understanding of the etiological mechanisms remains incomplete. This study quantitatively evaluated retinal vascular changes during an expedition to 4,167 m. Methods: Ten healthy participants summited Mount Toubkal, Morocco. Fundus images were taken predeparture, daily throughout the expedition, and 1 month postreturn. Diameter and tortuosity of four vessels were assessed, in addition to vessel density and features of HAR. Results: Significant (p ≤ 0.05) increases in tortuosity and diameter were observed in several vessels on high-altitude exposure days. There was a strong correlation between altitude and supratemporal retinal artery diameter on days 2, 3, and 6 of the expedition (r = 0.7707, 0.7951, 0.7401, respectively; p < 0.05). There was a significant increase in median vessel density from 6.7% at baseline to 10.0% on summit day. Notably there were no incidences of HAR. Conclusion: Physiological but not pathological changes were seen in this cohort, which gives insight into the state of the cerebral vasculature throughout this expedition. These results are likely attributable to relatively low altitude exposure, a conservative ascent profile, and the cohort's demographic. Future study must include daily retinal images at higher altitudes and take steps to mitigate environmental confounders. This study is relevant to altitude tourists, patients with diabetic retinopathy or retinal vein occlusion, and critically ill patients.

Retinal vascular changes in response to hypoxia

AbstractPurpose: Increased tortuosity and engorgement of retinal vasculature are recognized physiological responses to hypoxia. This can lead to high‐altitude retinopathy (HAR), which is a pathology seen in unacclimatised individuals at altitude. It typically features asymptomatic flame haemorrhages, but incidence reports are highly variable and our understanding of the aetiological mechanisms remains incomplete. This study aimed to evaluate retinal vascular changes throughout an expedition to 4167 metres.Methods: 10 healthy participants summitted Mount Toubkal, Morocco. Fundus images were taken on a handheld camera pre‐departure, daily throughout the expedition, and one‐month post‐return. Diameter and tortuosity of four vessels was assessed, in addition to vessel density and the presence of HAR.Results: Significant (p ≤ 0.05) increases in tortuosity and diameter were observed in some vessels on high‐altitude exposure days. There was a significant increase in vessel density on summit day only.Conclusions: This is the first study to report increased vessel density and no incidence of HAR. These results are likely attributable to relatively low altitude exposure, a conservative ascent profile, and the young, healthy demographic profile of participants. However, the study is limited by its small sample size, environmental confounding factors and semi‐subjective diameter measurements. Physiological but not pathological changes were seen in this cohort, which gives insight to the state of the cerebral vasculature throughout this expedition and builds on current understanding of retinal vascular changes in hypoxia. Future work must include daily retinal images of larger sample sizes at higher altitude and take steps to mitigate against environmental confounders. This work is relevant to altitude tourists, patients with diabetic retinopathy or retinal vein occlusion, and critically ill patients at sea level.

Thickened Retinal Nerve Fiber Layers Associated With High-Altitude Headache.

Purpose: This study aimed to quantify the different quadrants of the optic nerve head (ONH) and macular parameters and their changes during exposure to high altitude, and to assess their correlation with high-altitude headache (HAH). Methods: Spectral-domain optical coherence tomography (OCT) was used to quantify changes in the retinal structure in 109 healthy subjects during acute exposure to high altitude (3,700 m). Self-reported symptoms of HAH and acute mountain sickness AMS were assessed using Lake Louise Score (LLS), alongside measurements of physiological parameters (oxygen saturation [SpO2], heart rate [HR], hemoglobin level [Hb], and red blood cell [RBC] count). Measurements were taken before and after exposure to the high-altitude environment. The correlations of these parameters and changes at ONH were examined. Results: With the exposure to high altitude, the incidence of AMS was 44.0% and the frequency of HAH was 67.0% (54.1% mild, 12.9% moderate-severe). As for systemic parameters measured at high altitude, the participants exhibited significantly lower SpO2, higher resting HR, higher Hb, and a higher RBC (all p < 0.05). Key stereometric parameters used to describe ONH [superior, inferior, nasal, temporal, and mean retinal nerve fiber layer (RNFL) thickness] and macula (macular thickness) increased at high altitude compared with baseline. Most parameters of ONH changed, especially superior, inferior, and mean RNFL thickness (p < 0.05). There was a significant correlation between the ratios of RNFL at ONH and HAH [mean thickness (r = 0.246, p = 0.01); inferior (r = 0.216, p = 0.02); nasal (r = 0.193, p = 0.04)]. No associations between parameters of ONH and AMS or LLS were observed. Conclusion: The high-altitude environment can increase RNFL thickness at ONH. Furthermore, we found that the ratios of mean thickness, inferior area, and nasal area correlated positively with HAH, which provides new insights for understanding of the underlying pathological mechanisms of high-altitude retinopathy (HAR).

Hypoxia-induced inflammation: Profiling the first 24-hour posthypoxic plasma and central nervous system changes.

Central nervous system and visual dysfunction is an unfortunate consequence of systemic hypoxia in the setting of cardiopulmonary disease, including infection with SARS-CoV-2, high-altitude cerebral edema and retinopathy and other conditions. Hypoxia-induced inflammatory signaling may lead to retinal inflammation, gliosis and visual disturbances. We investigated the consequences of systemic hypoxia using serial retinal optical coherence tomography and by assessing the earliest changes within 24h after hypoxia by measuring a proteomics panel of 39 cytokines, chemokines and growth factors in the plasma and retina, as well as using retinal histology. We induced severe systemic hypoxia in adult C57BL/6 mice using a hypoxia chamber (10% O2) for 1 week and rapidly assessed measurements within 1h compared with 18h after hypoxia. Optical coherence tomography revealed retinal tissue edema at 18h after hypoxia. Hierarchical clustering of plasma and retinal immune molecules revealed obvious segregation of the 1h posthypoxia group away from that of controls. One hour after hypoxia, there were 10 significantly increased molecules in plasma and 4 in retina. Interleukin-1β and vascular endothelial growth factor were increased in both tissues. Concomitantly, there was significantly increased aquaporin-4, decreased Kir4.1, and increased gliosis in retinal histology. In summary, the immediate posthypoxic period is characterized by molecular changes consistent with systemic and retinal inflammation and retinal glial changes important in water transport, leading to tissue edema. This posthypoxic inflammation rapidly improves within 24h, consistent with the typically mild and transient visual disturbance in hypoxia, such as in high-altitude retinopathy. Given hypoxia increases risk of vision loss, more studies in at-risk patients, such as plasma immune profiling and in vivo retinal imaging, are needed in order to identify novel diagnostic or prognostic biomarkers of visual impairment in systemic hypoxia.

Integrative analysis of miRNA-mRNA network in high altitude retinopathy by bioinformatics analysis.

High-altitude retinopathy (HAR) is an ocular manifestation of acute oxygen deficiency at high altitudes. Although the pathophysiology of HAR has been revealed by many studies in recent years, the molecular mechanism is not yet clear. Our study aimed to systematically identify the genes and microRNA (miRNA) and explore the potential biomarkers associated with HAR by integrated bioinformatics analysis. The mRNA and miRNA expression profiles were obtained from the Gene Expression Omnibus database. We performed Gene Ontology functional annotations and Kyoto Encyclopedia of Genes and Genomes pathway analysis. Potential target gene analysis and miRNA–mRNA network analysis were also conducted. Quantitative RT-PCR (qRT-PCR) was used to validate the results of the bioinformatics analysis. Through a series of bioinformatics analyses and experiments, we selected 16 differentially expressed miRNAs (DE-miRNAs) and 157 differentially expressed genes related to acute mountain sickness (AMS) and constructed a miRNA–mRNA network containing 240 relationship pairs. The hub genes were filtered from the protein-protein interaction network: IL7R, FOS, IL10, FCGR2A, DDX3X, CDK1, BCL11B and HNRNPH1, which were all down-regulated in the AMS group. Then, nine up-regulated DE-miRNAs and eight hub genes were verified by qRT-PCR in our hypoxia-induced HAR cell model. The expression of miR-3177-3p, miR-369-3p, miR-603, miR-495, miR-4791, miR-424-5p, FOS, IL10 and IL7R was consistent with our bioinformatics results. In conclusion, FOS, IL10, IL-7R and 7 DE-miRNAs may participate in the development of HAR. Our findings will contribute to the identification of biomarkers and promote the effective prevention and treatment of HAR in the future.

Hesperidin ameliorates hypobaric hypoxia-induced retinal impairment through activation of Nrf2/HO-1 pathway and inhibition of apoptosis

High-altitude retinopathy is initiated by hypobaric hypoxia and characterized by retinal functional changes, but the precise cellular and molecular mechanisms that mediate this dysfunction remain unclear. The aim of our investigation is to determine the protective efficacy of hesperidin (HSD) on the hypobaric hypoxia-induced damage to the retina. Experiment rats were randomly grouped as the control, hypobaric hypoxia group and HSD intervention group. The hypobaric hypoxia and the HSD intervention groups were maintained in a low-pressure oxygen cabin. We found that hypobaric hypoxia dramatically reduced nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1(HO-1) levels, induced an elevation in immunostaining of TUNEL-positive cells. Hypobaric hypoxia exposure resulted in the increase of Bcl-2, decrease of caspase3 and caspase9 expression as well as Bax level. HSD protected the retina from hypobaric hypoxia-caused impairment by enhancing Nrf2 and HO-1 activation, attenuating apoptotic caspases levels, and reducing Bax and preserving Bcl-2 expression. Additionally, oxidative stress increased poly (ADP-ribose) polymerase 1 (PARP1) and suppressed ciliary neurotrophic factor (CNTF) level, HSD treatment reverted this effect by down-regulation of PARP1 and up-regulation of CNTF expression. Taken together, our findings implicate that HSD exerts a protective role in response to hypobaric hypoxia stress by activating Nrf2/HO-1 pathway and inhibiting apoptosis.

Branch retinal artery occlusion secondary to high-altitude exposure and diabetic retinopathy: a case report

BackgroundTo report a case of branch retinal artery occlusion (BRAO) secondary to high-altitude exposure and diabetic retinopathy (DR), and to characterize the retinal changes before and after hyperbaric oxygen (HBO) treatment.Case presentationWe present a case of a 42-year-old man with DR who travelled to Tibet (in China, 3800 m/12467 ft. above mean sea level). The day after the end of his journey, the patient presented with acute, painless visual loss and visual field loss in his left eye. He was then diagnosed with BRAO, which is an acute blockage of blood flow. After HBO treatment, visual acuity and visual field were improved.ConclusionsHigh-altitude exposure and DR may be considered as relevant risk factors for BRAO. The ophthalmologist should be aware that the BRAO might be a rare presenting sign of high-altitude retinopathy (HAR), particularly in patients with DR. HBO treatment can be considered as a choice for ophthalmologists on treatment against BRAO.

Ocular Presentations in High Altitude Sickness: Experience of Our Centre

Introduction: High altitude has various effects on human beings. Altitude-related illnesses are a frequent cause of morbidity and occasional mortality in travelers to high altitudes throughout the world. Altitude has potential undesired ophthalmological effects too. Most of these problems are primarily preventable with an adequate level of information before and during travel. In this article, ophthalmological effects like altitude retinopathy and other ocular presentations of high altitude, likely to be encountered by mountaineers, are reviewed.Materials and methods: This is a hospital-based cross-sectional study from March 2016 to March 2017 done in Swacon International Hospital and Sleep Care Center, Kathmandu, Nepal. All the patients diagnosed as acute mountain sickness in the hospital during the study period were included. All the patients were evaluated by a physician and an ophthalmologist. All the findings were recorded in the proforma.Results: A total of 167 patients were admitted. Among them, 98 patients were diagnosed with acute mountain sickness; 20 patients had High altitude cerebral edema and 40 had High altitude pulmonary edema. Ocular findings, among patients who presented to our centre, were a high altitude retinopathy (28.48%) corneal abrasions (5.6%), snow blindness (8.86%), acetazolamide induced myopia (2.53%), conjunctivitis(8.22%), corneal ulcer (1.26%) and retinal detachment(0.63%).Conclusions: Mountaineers are at risk of developing high-altitude-related illnesses. Many other tissues in the eyes are also affected by high-altitude hypoxia, and effects can be observed on the conjunctiva, cornea, intraocular pressure, lens, uvea apart from the retina and the optic nerve.

High Altitude Retinal Hemorrhage

Objective: sudden atmospheric pressure changes can generate vascular modifications in the retina. We present a clinical case of retinal hemorrhage related to high altitude and propose to revise its pathophysiology. Methods: A case presentation with review of literature. Results: 36 year old Male patient came to our institute with sudden diminished vision in the right eye associated with loss of consciousness while climbing a mountain. In the ophthalmological examination, we could appreciate in the right eye a macular hemorrhage and in both eyes few diffuse hemorrhages in mild periphery. The patient lost follow-up and return after 1 year for a check-up. He had spontaneous resolution of all hemorrhages. Conclusion: the acute mountain sickness affects mostly not climatized people. Changes in atmospheric pressure generate reduction of the partial pressure of oxygen in the blood. This can lead to vascular changes in the retina. This change may not appear if there is a proper climatization while climbing a mountain. The presence of high altitude retinopathy alerts about cerebral oedema related to high altitude.

Effects of Hypobaric Hypoxia on Rat Retina and Protective Response of Resveratrol to the Stress.

High-altitude retinopathy represents retinal functional changes associated with environmental challenges imposed by hypobaric hypoxia, but the detailed cellular and molecular mechanism underlying this process remains unclear. Our current investigation was to explore the effect of hypobaric hypoxia on the rat retina and determine whether resveratrol has a protective efficacy on the hypoxic damage to the retina. Experiment rats were randomly grouped as the control group, hypoxia group and resveratrol intervention group. The hypoxia group and the resveratrol intervention group were maintained in a low-pressure oxygen cabin, and the resveratrol intervention group was given daily intraperitoneal injections with resveratrol. We found that hypobaric hypoxia increased thioredoxin 1 (Trx1) and thioredoxin 2 (Trx2) expression in retinas, and resveratrol treatment significantly reversed these changes (P < 0.05, P < 0.05 respectively). In comparison with controls, hypoxia upregulated the mRNA expression levels of caspase3 (P < 0.001), caspase9 (P < 0.01), heat shock protein 70 (Hsp70) (P < 0.05), heat shock protein 90 (Hsp90) (P < 0.001) and hypoxia-inducible factor-1 (HIF-1) (P < 0.05). Resveratrol administration caused a significant decrease in the gene expression of caspase3 (P< 0.001), HSP90 (P < 0.05) and HIF-1 mRNA (P < 0.01) as well as an increase in HSP70 mRNA when compared with the hypoxia group. These findings indicated that resveratrol exerted an anti-oxidative role by modulating hypoxia stress- associated genes and an anti-apoptosis role by regulating apoptosis-related cytokines. In conclusion, hypobaric hypoxia may have a pathological impact on rat retinas. The intervention of resveratrol reverses the effect induced by hypobaric hypoxia and elicits a protective response to the stress.

Rétinopathie de haute altitude : à propos de 3 cas

To report three cases of vision loss occurring at high altitude. Three patients aged 27 to 52 years presented with scotoma and/or visual acuity deficit upon their return from high altitude expeditions above 6000 m. Fundus examination revealed multiple posterior pole hemorrhages, resolving completely by two months. Exposure to hypobaric hypoxia at high altitude leads to adaptation mechanisms in order to maintain retinal oxygenation. Certain individuals have an inadequate autoregulatory response and develop signs of "high altitude retinopathy" (HAR), including retinal hemorrhages most often, with occasional vitreous hemorrhage, optic nerve head edema and retinal vein occlusion. The pathophysiology of HAR is not well understood. Identified risk factors include altitude above 4000 m, rapid ascent and personal susceptibility. Age and fitness are unrelated. Association with acute mountain sickness, high-altitude pulmonary edema and high-altitude cerebral edema is still controversial. Retinal hemorrhages occurring after high-altitude hiking are an early manifestation of HAR and are part of high-altitude illness. HAR usually occurs at altitudes above 4000 m, is generally asymptomatic, and spontaneously regresses. A maladaptive autoregulatory response to hypobaric hypoxia appears to be the cause of HAR.

Increased choroidal thickness in patient with high-altitude retinopathy

We report a case of high-altitude retinopathy with increased choroidal thickness detected by spectral-domain optical coherence tomography (SD-OCT). A 36-year-old Japanese man developed an acute vision decrease in his left eye after he had trekked at an altitude of 4600 m in Tibet for 1 week. His visual acuity was 20/20 OD and 20/200 OS with refractive errors of − 0.25 diopters (D) OD and − 0.50 D OS 3 weeks after the onset of the visual decrease. Funduscopic examinations revealed multiple intraretinal hemorrhages bilaterally and a macular hemorrhage in the left eye. SD-OCT showed that the thickness of choroidal layer at the fovea was 530 μm OD and 490 μm OS which is thicker than that in normal subjects of approximately 300 μm. We suggest that the increase in the retinal blood flow under hypoxic conditions may be associated with an increase in the choroidal blood flow resulting in an increase in choroidal thickness.

High-altitude ophthalmic changes: An often overlooked entity

Letter to the EditorHigh-altitude ophthalmic changes: An often overlooked entityS. KapoorS. KapoorSchaumburg, IllinoisPublished Online:15 Sep 2013https://doi.org/10.1152/japplphysiol.00508.2013MoreSectionsPDF (28 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat to the editor: I read with great interest the recent article by Martinot et al. (4). One aspect of high-altitude exposure that is often overlooked is high-altitude-related ophthalmic changes.For instance, high-altitude exposure may result in “central retinal vein occlusion.” Symptoms consistent with occlusion may appear as early as 2 days after entering higher altitudes (2). On the other hand, retinal vein occlusion has been reported as much as a year after entering higher altitudes (5). Descent to lower altitudes is accompanied by complete resolution of the symptoms in most patients. Retinal hemorrhages may also develop (1). Similarly, vitreous hemorrhages may develop. Chronic exposure to high-altitude hypoxia may result in marked intraretinal angiogenesis. Sudden ascent to higher altitudes may also result in severe hypoxia that may significantly decrease “visual sensitivity,” particularly peripheral sensitivity. For instance, Horng et al. (3) in a recent study reported a significant decline in the “mean visual sensitivity” by 7.2 dB. A slightly decreased negative impact is also seen on central visual sensitivity.Ascent into higher altitudes may also result in the development of glaucoma secondary to altitude-associated accentuation of intraocular pressure. Ascent into higher altitudes is also associated with a resulting increase in the incidence of dry eyes. Incidence rates as high as 50% have been reported (1). A significant association is seen between a Schirmer test score of <5 mm and dry eye symptoms (3). Ascent into higher altitudes also results in accentuation of central corneal thickness. This is secondary to swelling of the corneal stroma secondary to hypoxia-induced endothelial changes (5). This results in a higher incidence of refractive errors in those exposed to high altitudes.It is obvious from the above examples that ascent into high altitude may cause acute as well as chronic ophthalmic changes. Physicians should be aware of these changes, especially in those who regularly have to ascend to high altitudes.DISCLOSURESNo conflicts of interest, financial or otherwise, are declared by the author(s).AUTHOR CONTRIBUTIONSAuthor contributions: S.K. drafted manuscript; S.K. edited and revised manuscript; S.K. approved final version of manuscript.REFERENCES1. Guo B, Lu P, Chen X, Zhang W, Chen R. Prevalence of dry eye disease in Mongolians at high altitude in China: the Henan eye study. Ophthalmic Epidemiol 17: 234–241, 2010.Crossref | ISI | Google Scholar2. Ho TY, Kao WF, Lee SM, Lin PK, Chen JJ, Liu JH. High-altitude retinopathy after climbing Mount Aconcagua in a group of experienced climbers. Retina 31: 1650–1655, 2011.Crossref | ISI | Google Scholar3. Horng CT, Liu CC, Wu DM, Chen JT, Chang CJ, Tsai ML. Visual fields during acute exposure to a simulated altitude of 7620 m. Aviat Space Environ Med 79: 666–669, 2008.Crossref | Google Scholar4. Martinot JB, Mule M, de Bisschop C, Overbeek MJ, Le-Dong NN, Naieje R, Guenard H. Lung membrane conductance and capillary volume derived from the NO and CO transfer in high altitude newcomers. J Appl Physiol 115: 157–166, 2013.Link | ISI | Google Scholar5. Morris DS, Somner JE, Scott KM, McCormick IJ, Aspinall P, Dhillon B. Corneal thickness at high altitude. Cornea 26: 308–311, 2007.Crossref | ISI | Google ScholarAUTHOR NOTESAddress for reprint requests and other correspondence: S. Kapoor, 75 Kristin Circle, Schaumburg, IL 60195 (e-mail: [email protected]com). Download PDF Previous Back to Top Next FiguresReferencesRelatedInformationCited ByHigh altitude hypoxia: An enigmaCurrent Medicine Research and Practice, Vol. 7, No. 6 More from this issue > Volume 115Issue 6September 2013Pages 949-949 Copyright & PermissionsCopyright © 2013 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.00508.2013PubMed24039258History Published online 15 September 2013 Published in print 15 September 2013 Metrics

Central Retinal Vein Occlusion Following Hypobaric Chamber Exposure

Mountain climbers who ascend to a high altitude could suffer high altitude retinopathy, which varies from tortuous retinal vessels and hemorrhages to retinal vascular obstruction. As hypobaric chamber training could imitate a fast ascent and could lead to decompression sickness, a simulated flight could also lead to a high altitude retinopathy. This paper will present a case of central retinal vein occlusion that occurred after exposure to a hypobaric chamber and Valsalva maneuver. Although the patient was treated with an intravitreal bevacizumab injection, his macular edema was aggravated after a helicopter flight, which involved re-exposure to high altitudes and a Valsalva maneuver. Systemic evaluation including blood coagulation and carotid Doppler studies did not reveal any lesion. Notably, central retinal vein occlusion can occur in young, healthy individuals after hypobaric chamber exposure.

Eye problems on expeditions

Visual loss in the wilderness setting is at best disabling and at worst potentially fatal. However many physicians have a poor knowledge of ophthalmology and the basic skills that could be applied in situations away from definitive care. This paper is intended for physicians, interested non-medical people and expedition operators as a practical guide to the treatment and prevention of eye problems on expeditions. Some of the eye conditions described in this paper are unique to the high altitude setting, such as high altitude retinopathy and some could happen in any environment, such as trauma, dry eyes and contact lens problems. As with any aspect of an expedition, preparation is vital to prevent and avoid eye problems. It is therefore important that pre-existing ocular conditions are known about and appropriate drugs and equipment are available in expedition first aid kits. In the event of a visual problem, it is always better to be cautious and evacuate a patient rather than a risk a sight-threatening complication. However this paper should provide a non-ophthalmologist with the skills to treat the eye conditions described.