The ocular surface is protected by the tear film and the eyelids. Tears are a triphasic matrix, produced by cells in the conjunctiva, lacrimal gland and lid – comprising of mucinous, aqueous and lipid phases which variously nourish, hydrate and stabilise the ocular surface. Deficiency in any of these phases may lead to degeneration of the ocular surface, which varies from mild gritty dry eyes to sight-threatening corneal ulceration.
The eyelids provide physical protection for the ocular surface. They consist of the posterior, conjunctival surface; a central structural component (the tarsal plate) and an anterior skin/muscle lamella. The levator palpebrae superioris muscle effects upper lid closure, whilst the orbicularis oculi muscle maintains the tone of the lower lid, keeping it effaced to the globe. The blink reflex, lid closure and upward deflection of the globe on lid closure (Bell’s phenomenon) all protect the ocular surface from environmental damage. An intact, smooth lid margin contour is also important in order to maintain stable tear film dynamics and healthy ocular surface.
Although the orbit and eyelids provide some degree of protection for the eye, specific points of anatomical weakness and vulnerability exist:
The orbital apex
Haemorrhage at the apex (retrobulbar haemorrhage) is a potentially blinding ophthalmic emergency which should be treated urgently, in the field if required (see instructions on Canthotomy and Cantholysis).
The orbital floor
Blowout fracture of the thin orbital floor resulting from blunt axial trauma can entrap muscle fibres of inferior rectus leading to tissue necrosis.
The optic nerve
Avulsion injuries to the nerve cause significant sight loss or blindness.
The lateral side of the globe
Bony protection of the lateral globe is poor.
The anterior surface of the globe
Penetrating injuries of the globe may occur, even through closed eyelids.
As the external surface of the adnexae, the eyelids are most exposed to potential traumatic injury.
33.2 Ametropia and the Correction of Refractive Error
Prevalence of refractive error varies around the world, with significantly higher rates of myopia (“short sightedness”) in Asian peoples. Clinically, important refractive error causing blurring of vision (ametropia) is thought to affect half of all adults in the USA, with rates of myopia appearing to increasing .
Prevalence of severe myopia (“short sightedness”), defined as a spherical equivalent prescription of less than or equal to −5.00 dioptres, is more than 7 % of adults aged between 20 and 59, which is the age group most likely to undertake extreme or wilderness sporting activities. Rates of hypermetropia (“long sightedness”) are lower; between 1 and 2.4 % of adults in the same age groups have a spherical equivalent of equal to or greater than +3.00 dioptres . Therefore, a large proportion of individuals undertaking extreme or wilderness sporting activities will require refractive correction. The specific visual demands of particular sporting activities may place extra requirements and result in the use of refractive correction which might not be required in normal activities.
The choice of ametropic correction depends on the degree of refractive correction required, the amount the error interferes with sporting activities, the environment in which the sport is undertaken, specific anatomical considerations and individual preference.
Refractive correction options available are:
External correction (glasses/contact lenses)
In-plane correction (corneal refractive surgery)
Internal correction (phakic intraocular lens (IOL) implantation or clear lens extraction and IOL implantation)
Each has merits and limitations and may have particular considerations in the context of extreme sports:
Glasses or spectacle lenses can adequately correct most refractive errors, although correction of very high and low prescriptions with glasses may induce chromatic and spherical aberrations which can be just as troublesome as the initial visual blurring. Varifocal or bifocal glasses provide excellent correction for near and distance, which is relevant in presbyopic individuals where accommodative function is reduced (over the age of 45), and are usually well tolerated.
Glasses also provide an extra physical protection for the eye and adnexa, and refractive correction may be incorporated into snow goggles, sunglasses and diving goggle lenses. Furthermore, the use of photochromatic lenses (“light reactors”) provides effective UV filtering with refractive correction.
However, glasses may become a distracting or dangerous encumbrance, in particular when their effect is negated by the environment. This is particularly the case for water sports, bungee jumping and free-fall/static line parachuting. In these cases, contact lenses may be more appropriate.
In extremis when glasses or sunglasses have been lost or broken, a pinhole punched through a piece of card or bark functions as rudimentary glasses and will allow for evacuation from remote environments; this will also serve to protect the eyes from ultraviolet light.
33.2.2 Contact Lenses
Around 5 % of the population aged between 15 and 64 wear contact lenses, the vast majority wearing soft hydrogel or daily disposable lenses [3, 4]. Contact lenses can adequately correct refractive errors of a similar range to that of glasses and are less prone to the refractive aberrations which are characteristic of higher prescriptions in glasses.
Care for contact lenses, personal hygiene and strict adherence to wear schedules and rest periods reduces the risk of serious infection related to contact lens wear, which may be blinding. These infections are over five times more likely in multi-use soft lenses than daily disposables , and the use of disposable lenses in preference to multi-use lenses for extreme and wilderness sports should be encouraged.
One of the major advantages of contact lenses, when compared with glasses, is that they can be used in the water. Between 52.7 and 60 % of contact lens wearers habitually use them whilst swimming or surfing [3, 5]. However, the risk of serious infection is significantly increased with this practice, in particular protozoan infection (Acanthamoeba spp.) which is associated with a grave visual prognosis if there is a delay to diagnosis and appropriate management . The refractive and practical advantages of contact lens use for water sports are clear, but it is important to educate participants to use fresh, disposable lenses for the duration of the activity only, removing them immediately afterwards, and to seek early expert medical attention if signs of symptoms of infection appear (pain, redness or blurred vision).
33.2.3 Photorefractive Surgery (LASEK, LASIK and PRK)
Photorefractive surgery (“laser eye surgery”) for the in-plane correction of ametropia and astigmatism has found a strong market in young adults who participate in extreme and wilderness sports. The risks associated with contact lens wear and the inconvenience of glasses are obviated, and in most cases, patients vision is improved to a level where participation in sports is possible.
Although laser in situ keratomileusis (LASIK) remains the most popular modality of photorefractive surgery, increasing numbers of refractive surgeons are undertaking surface ablation techniques (LASEK, PRK and sub-epithelial keratectomy) to correct low to moderate refractive error or in patients where traditional LASIK is not appropriate.
In general terms, the laser-refractive techniques can be split in into those that create a flap of healthy corneal epithelium ± superficial stroma, which is then replaced after ablation of the stromal bed, and those that ablate the surface directly or remove the epithelium before ablation. Recovery times, post-operative discomfort and infection risks are lower in the flap group (LASIK) but problems with flap/bed interface adherence, lamellar keratitis and changes in the structural integrity of the cornea (causing unpredictable refractive changes and the potential for traumatic loss of the flap) are generally not seen in the non-flap group. Most photorefractive surgery undertaken currently is LASIK, although a slow trend towards non-flap (surface ablation) techniques is well documented .
33.2.4 Surgical Approaches to Ametropia
Modern advances in surgical technique and implant choice have led to an increasing trend towards refractive surgery for young patients with moderate to high refractive error and especially with presbyopic patients over the age of 45. The choice of surgical techniques is wide and may involve replacement of the natural crystalline lens with a synthetic intraocular lens (IOL) (clear lens extraction) or implantation of an IOL in an eye in which the crystalline lens remains (phakic IOL implantation). The choice of approach depends on the specific refractive error and the visual requirements of the patient. IOL placement is most commonly behind the iris (either in the ciliary sulcus or the lens capsule), but the increasing use of modern anterior chamber and iris clip lenses (particularly in phakic IOL procedures) present specific considerations in the case of extreme and wilderness sports. High degrees of ametropia and astigmatism can be corrected with modern IOLs, many of which also offer a degree of multifocality or pseudo-accommodation in order to allow the pre-presbyope to continue to function without glasses.
All intraocular surgery carries risk of infection and sight loss or blindness. The structural integrity of the eye is compromised following surgery, and case reports exist of traumatic expulsion of the contents of the eye following direct trauma to the eye years after modern cataract surgery  although these are very much less likely with modern techniques. Ultraviolet light is absorbed by the crystalline lens but not by clear IOLs. For this reason, blue light filtering (yellow) IOLs have been developed and are in use. The evidence for significant retinal damage in patients with clear IOLs is not clear cut, and the use of these lenses should not preclude individuals from undertaking sporting activities in high ambient UV conditions, provided that suitable ocular UV protection is used.
33.3 Pre-existing Ocular Conditions
The only ocular condition which excludes ascent to high altitude or even air travel is the immediate post-operative period following the use of intraocular gas in retinal surgery as this can expand and potentially cause a central retinal artery occlusion .
Environmental factors may exacerbate existing ocular conditions; in particular ocular surface disease and consideration should be given to prophylaxis in these circumstances.
33.3.1 Monocular Vision
People with useful vision in only one eye should take extra care to protect their eyes from both the sun and objective dangers such as sand, ice and rock. It is therefore advisable to have specially designed polycarbonate safety glasses for any activities where flying debris could enter the eye.
33.3.2 Dry Eye
Dry eye is a multifactorial condition, which is frequently overdiagnosed and treated. However, arid and high ambient UV conditions such as those found in deserts and alpine environments may exacerbate existing disease, and there is a small risk of sight-threatening corneal ulceration in dry eye disease. It is sensible to use lubricating eye drops, especially in these adverse environmental conditions. A balance should always be struck between using a drop sufficiently viscous to give adequate benefit, without being so thick as to impair vision, and preservative-free drops should be used in contact lens wearers.
33.3.3 Cataract Surgery
There are no special precautions required for people who have an intraocular lens following cataract surgery or clear lens extraction who want to partake in extreme sports. Whilst no studies have been undertaken to establish the safety of extreme sports in pseudophakic patients, there is plenty of anecdotal evidence from extreme sportspeople, mountaineers, aviators and even astronauts.
People on topical medication (drops) to reduce their intraocular pressure (IOP) in glaucoma should continue them as normal. There is no evidence to suggest that people with glaucoma cannot partake in extreme sports, but a full eye check is recommended before travel for any length of time, especially to high altitude. Acetazolamide (Diamox) used for the prophylaxis or treatment of acute mountain sickness in glaucoma patients could have a double effect as it significantly lowers IOP.
Diabetes mellitus is not a contraindication to extreme sports. However, each individual will need to be more vigilant of his or her blood glucose levels when partaking in sporting activity. Advice should be sought about the best method for glycaemic control depending on the anticipated activity together with how often blood sugar should be checked, and other people partaking in sport with diabetics should be aware of the signs of hypoglycaemia and its treatment.
There is no evidence that high altitude causes or exacerbates diabetic retinopathy . Diabetic people also do not appear to be at any greater risk of high-altitude retinopathy. However, diabetics should maintain strict glycaemic control and acclimatise sensibly to avoid systemic or ocular consequences.
33.3.6 Retinal Surgery
There is some evidence that retinal detachment may be induced at high altitude  in susceptible individuals, but once a detachment has been repaired successfully, there should be no risk at altitude. However, if a person has recently had retinal surgery with intraocular gas, they should not go into any environment where atmospheric pressure is changed: this includes air travel, high altitude and SCUBA diving. People should not travel by air until the intraocular gas has been absorbed; this can be more than a month. Silicone oil in the eye or retinal buckle surgery is not contraindications to air travel. People who have had recent retinal surgery should consult their ophthalmologist for advice on travel.
33.4 Extreme Sports at High Altitude (Hypobaria)
Extreme sports undertaken at altitude include mountaineering, high-altitude trekking, snow sports, hang gliding, paragliding and parachuting.
In general, the risks to ocular health at altitude are those related to the environment. Low atmospheric oxygen concentrations, high ambient ultraviolet radiation levels, low temperatures and co-morbid physiological changes (such as acute mountain sickness) may all have an effect on ocular health.
33.4.1 UV Exposure
High ambient UV radiation, in particular UV-A (320–400 nm) and UV-B (290–320 nm), is known to be carcinogenic, and whilst UV-B has historically been considered to have the greatest effect, increasing evidence suggests a key role for UV-A in tumour development. Skin tumours of the eyelids and adnexae comprise 5–10 % of all skin cancers – most of these are basal cell carcinoma (BCC) or squamous cell carcinoma (SCC). Indeed, non-melanoma skin cancer is the most commonly diagnosed tumour in men in the USA . Increasing rates of outdoor sports participation and thinning of the ozone layer have been associated with growing rates of cutaneous melanoma particularly in high latitudes; the rates in more temperate parts of the world have stabilised – probably due to improved understanding, education and prevention. The risk of skin cancers of this type is known to be dose dependent, and thus short periods of time spent at altitude, for example, during parachuting are unlikely to carry a significantly increased risk. There is good evidence to back up theories that long-term high-altitude activities are a positive predictor for developing skin cancer and precancerous disease (solar keratosis) . Significant episodes of sunburn are associated with increased rates of BCC, and so prudent UV-A/B protection should be practised in these environments with sun-protective clothing, sunglasses, hats and judicious use of sunscreen and lip balm [18, 19].