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Photokeratitis | |
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Specialty | Ophthalmology ![]() |
Photokeratitis or ultraviolet keratitis is a painful eye condition caused by exposure of insufficiently protected eyes to the ultraviolet (UV) rays from either natural (e.g. intense direct or reflected sunlight) or artificial (e.g. the electric arc during welding) sources. Photokeratitis is akin to a sunburn of the cornea and conjunctiva.
The injury may be prevented by wearing eye protection that blocks most of the ultraviolet radiation, such as welding goggles with the proper filters, a welder's helmet, sunglasses rated for sufficient UV protection, or appropriate snow goggles. The condition is usually managed by removal from the source of ultraviolet radiation, covering the corneas, and administration of pain relief. Photokeratitis is known by a number of different terms including: snow blindness, arc eye, welder's flash, bake eyes, corneal flash burns, flash burns, niphablepsia, or keratoconjunctivitis photoelectrica.
Common symptoms include pain, intense tears, eyelid twitching, discomfort from bright light, [1] and constricted pupils.
Any intense exposure to UV light can lead to photokeratitis. [2] In 2010, the Department of Optometry at the Dublin Institute of Technology published that the threshold for photokeratitis is 0.12 J/m2. [3] (Prior to this, in 1975, the Division of Biological Effects at the US Bureau of Radiological Health had published that the human threshold for photokeratitis is 50 J/m2. [4] ) Common causes include welding with failure to use adequate eye protection such as an appropriate welding helmet or welding goggles. This is termed arc eye, while photokeratitis caused by exposure to sunlight reflected from ice and snow, particularly at elevation, is commonly called snow blindness. [5] It can also occur due to using tanning beds without proper eyewear. Natural sources include bright sunlight reflected from snow or ice or, less commonly, from sea or sand. [6] Fresh snow reflects about 80% of the UV radiation compared to a dry, sandy beach (15%) or sea foam (25%). This is especially a problem in polar regions and at high altitudes, [5] as with about every 300 m (1,000 ft) of elevation (above sea level), the intensity of UV rays increases by four percent. [7]
Fluorescein dye staining will reveal damage to the cornea under ultraviolet light. [8]
Photokeratitis can be prevented by using sunglasses or eye protection that transmits 5–10% of visible light and absorbs almost all UV rays. Additionally, these glasses should have large lenses and side shields to avoid incidental light exposure. Sunglasses should always be worn, even when the sky is overcast, as UV rays can pass through clouds. [9]
The Inuit, Yupik, and other Arctic peoples have carved snow goggles from materials such as driftwood or caribou antlers to help prevent snow blindness for millennia. [10] Curved to fit the user's face with a large groove cut in the back to allow for the nose, the goggles allow in a small amount of light through a long thin slit cut along their length. The goggles are held to the head by a cord made of caribou sinew. [11]
In the event of missing sunglass lenses, emergency lenses can be made by cutting slits in dark fabric or tape folded back onto itself. [12] The SAS Survival Guide recommends blackening the skin underneath the eyes with charcoal (as the ancient Egyptians did) to avoid any further reflection. [13] [14]
Explorers of the polar regions employed various methods and materials to protect their eyes from the harsh glare in snowy environments. Edward Evans noted the popularity of yellow and orange-tinted glasses among explorers, though some showed a preference for green. Despite the availability of blue and purple glasses, Atkinson advised that all glasses, regardless of colour, should undergo spectroscope testing to ensure effectiveness.
Robert Scott favoured a more rudimentary approach, opting for goggles crafted from leather or wood with narrow slits, which prevented the accumulation of frost. A similar design principle was also applied in emergency situations, such as when the Swedish expedition, after being shipwrecked, fashioned makeshift goggles from wood or wire frames covered with fabric from a Swedish flag.
The Royal Geographical Society’s guidance for travellers included a technique used by indigenous peoples of high-altitude regions, which involved darkening the skin around the eyes and nose to mitigate the risk of snow blindness. This method was adopted by the Terra Nova northern party in the absence of traditional goggles.
The impact of snow blindness extended to animals as well; the expedition’s horses suffered from the condition. Oates proposed dyeing the horses’ forelocks as a preventative measure, and they were also equipped with tassels over their eyes for protection. Similarly, mules were provided with canvas snow goggles, demonstrating the breadth of strategies developed to combat this pervasive issue during polar exploration. [15]
The pain may be temporarily alleviated with anaesthetic eye drops for the examination; however, they are not used for continued treatment, [16] as anaesthesia of the eye interferes with corneal healing, and may lead to corneal ulceration and even loss of the eye. [17] Cool, wet compresses over the eyes and artificial tears may help local symptoms when the feeling returns. Nonsteroidal anti-inflammatory drug (NSAID) eyedrops are widely used to lessen inflammation and eye pain, but have not been proven in rigorous trials. Systemic (oral) pain medication is given if discomfort is severe. Healing is usually rapid (24–72 hours) if the injury source is removed. Further injury should be avoided by isolation in a dark room, removing contact lenses, not rubbing the eyes, and wearing sunglasses until the symptoms improve. [5]
Ultraviolet (UV) light is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight, and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs, Cherenkov radiation, and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights.
Electromagnetic radiation can be classified into two types: ionizing radiation and non-ionizing radiation, based on the capability of a single photon with more than 10 eV energy to ionize atoms or break chemical bonds. Extreme ultraviolet and higher frequencies, such as X-rays or gamma rays are ionizing, and these pose their own special hazards: see radiation poisoning. The field strength of electromagnetic radiation is measured in volts per meter (V/m).
Glasses, also known as eyeglasses and spectacles, are vision eyewear with clear or tinted lenses mounted in a frame that holds them in front of a person's eyes, typically utilizing a bridge over the nose and hinged arms, known as temples or temple pieces, that rest over the ears.
Contact lenses, or simply contacts, are thin lenses placed directly on the surface of the eyes. Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision or for cosmetic or therapeutic reasons. In 2010, the worldwide market for contact lenses was estimated at $6.1 billion, while the US soft lens market was estimated at $2.1 billion. Multiple analysts estimated that the global market for contact lenses would reach $11.7 billion by 2015. As of 2010, the average age of contact lens wearers globally was 31 years old, and two-thirds of wearers were female.
Sunglasses or sun glasses are a form of protective eyewear designed primarily to prevent bright sunlight and high-energy visible light from damaging or discomforting the eyes. They can sometimes also function as a visual aid, as variously termed spectacles or glasses exist, featuring lenses that are colored, polarized or darkened. In the early 20th century, they were also known as sun cheaters.
A pterygium of the eye is a pinkish, roughly triangular tissue growth of the conjunctiva onto the cornea of the eye. It typically starts on the cornea near the nose. It may slowly grow but rarely grows so large that it covers the pupil and impairs vision. Often both eyes are involved.
Keratitis is a condition in which the eye's cornea, the clear dome on the front surface of the eye, becomes inflamed. The condition is often marked by moderate to intense pain and usually involves any of the following symptoms: pain, impaired eyesight, photophobia, red eye and a 'gritty' sensation. Diagnosis of infectious keratitis is usually made clinically based on the signs and symptoms as well as eye examination, but corneal scrapings may be obtained and evaluated using microbiological culture or other testing to identify the causative pathogen.
Goggles, or safety glasses, are forms of protective eyewear that usually enclose or protect the area surrounding the eye in order to prevent particulates, water or chemicals from striking the eyes. They are used in chemistry laboratories and in woodworking. They are often used in snow sports as well, and in swimming. Goggles are often worn when using power tools such as drills or chainsaws to prevent flying particles from damaging the eyes. Many types of goggles are available as prescription goggles for those with vision problems.
A red eye is an eye that appears red due to illness or injury. It is usually injection and prominence of the superficial blood vessels of the conjunctiva, which may be caused by disorders of these or adjacent structures. Conjunctivitis and subconjunctival hemorrhage are two of the less serious but more common causes.
Keratoconjunctivitis is a term used to describe inflammation of both the cornea and the conjunctiva. This condition can have various causes, and its presentation may vary depending on the underlying factors.
Eye protection is protective gear for the eyes, and sometimes face, designed to reduce the risk of injury. Examples of risks requiring eye protection can include: impact from particles or debris, light or radiation, wind blast, heat, sea spray or impact from some type of ball or puck used in sports.
Corneal abrasion is a scratch to the surface of the cornea of the eye. Symptoms include pain, redness, light sensitivity, and a feeling like a foreign body is in the eye. Most people recover completely within three days.
Corneal cross-linking (CXL) with riboflavin (vitamin B2) and UV-A light is a surgical treatment for corneal ectasia such as keratoconus, PMD, and post-LASIK ectasia.
A welding helmet is a type of personal protective equipment used in performing certain types of welding to protect the eyes, face, and neck from flash burn, sparks, infrared and ultraviolet light, and intense heat. The modern welding helmet used today was first introduced in 1937 by Willson Products.
Corneal ulcer, also called keratitis, is an inflammatory or, more seriously, infective condition of the cornea involving disruption of its epithelial layer with involvement of the corneal stroma. It is a common condition in humans particularly in the tropics and in farming. In developing countries, children afflicted by vitamin A deficiency are at high risk for corneal ulcer and may become blind in both eyes persisting throughout life. In ophthalmology, a corneal ulcer usually refers to having an infection, while the term corneal abrasion refers more to a scratch injury.
Sunburn is a form of radiation burn that affects living tissue, such as skin, that results from an overexposure to ultraviolet (UV) radiation, usually from the Sun. Common symptoms in humans and other animals include red or reddish skin that is hot to the touch or painful, general fatigue, and mild dizziness. Other symptoms include blistering, peeling skin, swelling, itching, and nausea. Excessive UV radiation is the leading cause of (primarily) non-malignant skin tumors, which in extreme cases can be life-threatening. Sunburn is an inflammatory response in the tissue triggered by direct DNA damage by UV radiation. When the cells' DNA is overly damaged by UV radiation, type I cell-death is triggered and the tissue is replaced.
Vision of humans and other organisms depends on several organs such as the lens of the eye, and any vision correcting devices, which use optics to focus the image.
Glassblower's cataracts are a form of cataract due to an occupational exposure. They are formed by many years or decades of exposure to infrared radiation while working in the occupation of glass blowing, or working close to hot or molten metals such with metal foundry workers or blacksmiths. Glassblower's cataracts are due to chronic exposure to infrared radiation emitted due to the extreme heating of glass or molten metal. The infrared radiation is absorbed by the iris and lens of the eye. This causes cataracts after decades of exposure. This condition may be prevented by wearing protective glasses while practicing these occupations.
Photophthalmia is ophthalmia or inflammation of the eye, especially of the cornea and conjunctiva due to exposure to intense light of short wavelength, as in snow blindness.
Exposure keratopathy is medical condition affecting the cornea of eyes. It can lead to corneal ulceration and permanent loss of vision due to corneal opacity.