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Snow Blindness

Snow Blindness

Snow Blindness 150 150 Endeavour Medical

Snow Blindness

AUTHOR: RHYS TAYLOR

What is Snow Blindness?

Snow blindness is a term used to describe a form of photokeratitis: i.e. a burn to the cornea and conjunctiva. 

Photokeratitis occurs when the eyes are exposed to significant ultraviolet (UV) rays. This can be due to artificial exposure e.g. from welding arcs (‘arc eye’ or ‘welder’s eye’), tanning beds, or due to concentrated natural exposure.

Snow blindness occurs after prolonged exposure to  natural UV rays. Snow reflects up to 90% of UV rays [1]. As snow is often encountered in mountainous terrain, this risk is compounded by the increase in UV exposure which occurs at altitude (approximately 4% for every 300m climbed) [2]. These combined factors result in a doubling of UV light exposure at 2000m compared with sea level [3]. It is a well-documented issue, which has dogged many legendary expeditions such as that of Scott’s Terra Nova Antarctic expedition (1910 – 1913) [4].

Pathophysiology:

Whilst the cornea transmits light in the visible spectrum, UV rays are absorbed by the corneal epithelium. This process causes damage to the epithelial layer and results in a delayed sloughing of this superficial layer [5].

Photokeratitis is painful, as when this epithelial layer sheds it leaves the underlying nerve plexus exposed [6]. 

Signs and symptoms:

Symptom onset is usually six to twelve hours following UV exposure; however, this is exposure dependent and symptoms can occur as soon as one-hour post-exposure [7].

Symptoms include:

Bilateral red, painful, gritty eyes with associated photophobia [2].

Patients may be teary, have blurred vision or even suffer temporary blindness in severe cases.

Patients are likely to have surrounding sunburn to the face and eyelids as a diagnostic clue.

Differential diagnosis:

Be mindful not to miss critical ophthalmological diagnoses [2]. 

Signs such as systemic upset, concurrent illness, and unilateral changes should raise suspicion of alternative diagnoses. If there is painless loss of vision then this should be taken extremely seriously.

Similarly, if an individual has taken appropriate precautionary measures to prevent snow blindness, it is important not to develop an anchoring or confirmation bias prior to excluding differentials:

Acute angle closure glaucoma – Acute onset, painful with systemic upset.

Viral conjunctivitis – Can appear similar to snow blindness, however typically starts in one eye.

Contact lens overwear – Based on the history.

Dry eye – Based on the history, contact lens use, response to lubricants.

Foreign body – Based on history and a precipitating event.

High altitude retinopathy – Visual changes, usually painless in nature.

Painless loss of vision – Consider retinal detachment, vitreous haemorrhage, central retinal artery or vein occlusion, cerebral ischaemia, etc. 

Treatment:

Snow blindness will resolve spontaneously in 24 to 48 hours. Care is focused on symptom control and prevention of complications [7].

Patients should rest, avoid light and consider eye dressings to aid comfort. Cooling with cold compresses is a soothing option which is not resource intensive.

Lubricating drops and ointment can be used to manage the dry, gritty sensation.

Oral analgesia should be used, as can cycloplegic drops (e.g. cyclopentolate) to relieve the pain of ciliary spasm.

Adjunct treatments include antibiotic ointment to reduce the rate of secondary infections. 

Local anaesthetic should only be used to aid examination or facilitate evacuation in dangerous settings.

Prevention:

Snow blindness is prevented by minimising corneal exposure to UV rays.

Goggle or sunglasses with protective side pieces are recommended; ideally category 3 or 4 with 100% UV protection. 

Depending on the group size, duration and remoteness of the trip, it would be sensible to consider carrying some spares for the group. Eye protection should also have a hard-case container for storage when not in use and be easily accessible when needed.

In emergencies, sun shields can be made out of most materials by carving a slit into them for the eyes and fixing the material to the head. The small slits minimise refractive UV ray exposure. [2]

Are you interested in learning more about polar medicine?

If so, why not check out our Norway Polar Expedition course? 

Bibliography:

  1. Ambach W, Blumthaler M, Schöpf T. Increase of biologically effective ultraviolet radiation with altitude. Journal of wilderness medicine 1993;4(2):189-197.
  2. Morris DS, Mella S, Depla D. Official Standards of the UIAA Medical Commission: Eye Problems on Expeditions. The International Mountaineering and Climbing Federation 2010.
  3. Ellerton JA, Zuljan I, Agazzi G, Boyd JJ. Eye Problems in Mountain and Remote Areas: Prevention and Onsite Treatment—Official Recommendations of the International Commission for Mountain Emergency Medicine ICAR MEDCOM. Wilderness Environ Med 2009;20(2):169-175.
  4. Guly, Henry R.,F.R.C.P., F.C.E.M. Snow Blindness and Other Eye Problems During the Heroic Age of Antarctic Exploration. Wilderness Environ Med 2012;23(1):77-82.
  5. Podskochy A. Protective role of corneal epithelium against ultraviolet radiation damage. Acta Ophthalmol Scand 2004;82(6):714-717.
  6. Bergmanson JPG. Corneal Damage in Photokeratitis???Why Is It So Painful? Optometry Vision Sci 1990;67(6):407-413.
  7. The College of Optometrists. Clinical Management Guidelines: Photokeratitis. 2022; Available at: https://www.college-optometrists.org/clinical-guidance/clinical-management-guidelines/photokeratitis_ultraviolet_uv_burn_arceye_snowblin. Accessed 09/11/, 2023.

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