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ULTRAVIOLET KERATITIS

Ultraviolet keratitis, also known as photokeratitis or corneal flash burns, is a painful condition in which there is inflammation of the cornea of the eye.

WHAT IS ULTRAVIOLET KERATITIS?

Photokeratitis is a painful condition in which there is inflammation of the cornea of the eye. The cornea is the clear, firm cap that protects the pupil and the iris (colored part of the eye). It is caused by exposure of unprotected eyes to ultraviolet waves from the sun or from artificial sources. Ultraviolet keratitis can be thought of as a sunburn to the corneal epithelium (outermost layer of cells) and the conjunctiva. It is not usually noticed until several hours after exposure.

WHAT CAUSES ULTRAVIOLET KERATITIS?

Ultraviolet waves are the most common cause of radiation injury to the eye. Ozone in the atmosphere filters most of the harmful ultraviolet waves. For this reason, the sun rarely causes injury to the eyes after short exposures. The cornea absorbes most ultraviolet (UV) radiation that reaches the eye and damage to the corneal epithelium is cumulative. The ultraviolet waves burn the cells that make up the corneal epithelium, resulting in inflammation.

Any intense unprotected exposure to ultraviolet light can lead to corneal flash burns. A well-known admonition against exposure to natural UV radiation is that we should not look directly at the sun during a solar eclipse. However, this event is relatively rare.

There are other sources of ultraviolet waves that are far more common. For example, exposure to the sun on highly reflective snow fields at high elevations can result in direct injury to the corneal epithelium. This condition is known as snow blindness. In fact, prolonged exposure to sunlight from any reflective surface (e.g. ice, water, sand, bleached concrete pavement) can lead to corneal flash burns, although snow at high elevations is the most dangerous. The reason for this is that fresh snow has a reflective index of about 80% for UV radiation compared to sand at 15% or sea foam at 25%. Elevation also is a factor. For every 1000 feet (304.8 meters) of elevation above sea level, the intensity of ultraviolet waves increases by four percent.

Artificial sources of UV radiation also can cause corneal flash burns. For example, injury from unprotected exposure to a welder's arc is called arc eye. Other artificial sources of ultraviolet waves include:

carbon arcs.
suntanning beds.
photographic flood lamps.
lightning.
electric sparks.
halogen desk lamps.

Prolonged exposures to ultraviolet waves can lead to chronic solar toxicity, which is associated with several ocular surface disorders. Among these are pinguecula and pterygium, climatic droplet keratopathy, squamous metaplasia, carcinoma. The only ocular cancer associated with UV radiation is epidermoid carcinoma of the bulbar conjunctiva, which occurs with increased frequency in the tropics and subtropics.

HOW DOES ULTRAVIOLET KERATITIS AFFECT THE EYE?

Ultraviolet waves irritate the corneal epithelium, resulting in an inhibition of cell division, the fragmentation of cellular nuclear material, and subsequent loosening of the epithelial layer. This leads to an inflammatory response, including edema and congestion of the conjunctiva and a stippling of the corneal epithelium known as superficial punctate keratitis (SPK). The main characteristic of SPK is small pinpoint defects in the corneal epithelium that stain with a blue dye called fluorescein. If the SPK associated with photokeratitis is severe, it may be followed by total separation of the corneal epithelium cells from those underneath (epithelial desquamation), with swelling of the conjuntiva (conjunctival chemosis), tearing (lacrimation), and twitching of the eyelids (blepharospasm). Healing of the corneal epithelium layer usually occurs within 36-72 hours, and long-term problems are rare.

WHAT ARE SYMPTOMS OF ULTRAVIOLET KERATITIS?

Common symptoms of photokeratitis include:

eye pain (described as like having sand poured into the eyes).
blurred vision.
eye redness.
excessive tearing.
foreign body sensation in the eye.
increased sensitivity to bright light (photophobia).
headache.
constricted pupils.
eyelid twitching (blepharospasm).

Symptoms tend to occur 6-12 hours after injury. They typically resolve spontaneously within 36-72 hours, although constriction of the pupils may last as long as 96-128 hours.

HOW CAN I PREVENT ULTRAVIOLET KERATITIS?

Photokeratitis can be prevented by using sunglasses or other eye protection that transmits 5–10% of visible light and absorbs almost all UV radiation. The sunglasses should have large lenses and side shields to avoid incidental light exposure, which also can lead to corneal flash burns. UV protection measures should be used even when the sky is overcast, as ultraviolet rays can pass through clouds and burn the corneal epithelium. For welders, goggles or a welder's helmet containing the proper filters should always be used, even for short uses of the welding equipment. For skiers and other snow sports, snow goggles that block nearly all UV radiation should always be used. Swimmers and those involved in other water sports should always use UV protective goggles. Those working outside, particularly around concrete surfaces, should wear sunglasses with UV protection.

HOW IS ULTRAVIOLET KERATITIS TREATED?

Many cases of photokeratitis heal within 36-72 hours, without a need for specific treatment. When necessary, the goal of photokeratitis therapy is to treat the pain associated with damage in the corneal epithelium resulting from exposure to ultraviolet waves and to prevent infection while the cornea heals. Medications used include topical cycloplegics, ophthalmic anesthetics, ophthalmic and parenteral nonsteroidal anti-inflammatory drugs (NSAIDs), and other analgesics.

If your ophthalmologist suspects that you have ultraviolet keratitis, she or he usually will flush your eyes for several minutes with water or saline solution. Confirmation of corneal flash burns is made by applying a fluorescein stain and observing the cornea for the presence of SPK.

The following medications may be used to manage your case of photokeratitis.

Ophthalmic anesthetics are indicated for pain relief. Local anesthetics stabilize the membranes of neurons and prevent the initiation and transmission of nerve impulses, thereby producing the local anesthetic action.

Proparacaine 0.5% (Alcaine, Ophthetic) eye drops have a rapid onset of anesthesia that begins 13-30 seconds after administration. However, they have a short duration of action that lasts only for about 15-20 minutes. This medication is used to provide immediate relief to the patient during an examination and should not be used outside of a clinical setting. Typically 2-3 drops are instilled into the affected eye.

Cycloplegics relax ciliary muscle spasms that can cause a deep aching pain and photophobia. Cycloplegics are used to facilitate eye examination and provide relief of symptoms in patients with moderate-to-severe eye injury. These usually are given to the patient to provide immediate relief during the examination. Because cycloplegic medications also are mydriatic agents (dilate pupils), they are contraindicated for patients with certain types of glaucoma.

Cyclopentolate 0.5-1% (Cyclogyl). The usual dosage is one drop of 1% solution. This is repeated every 5-10 minutes as needed until the exam is finished.

Systemic analgesics are medications used to manage pain. Although most non-steroidal anti-inflammatory drugs (NSAIDs) are used primarily for their anti-inflammatory effects, they are effective analgesics and are useful for the relief of mild to moderate pain. Control of pain is essential to quality patient care for photokeratitis. NSAIDs are preferred because they do not have the side effect of raising intraocular pressure that is observed with steroid-containing anti-inflammatory medications.

Ibuprofen (Motrin, Advil, Nuprin, Rufen) usually is the drug of choice for mild to moderate pain, if no contraindications exist. This is because it inhibits both inflammatory reactions associated with corneal flash burns and pain. The usual dosage is 200-800 mg by mouth every 4-6 hours, while symptoms persist. The overall dosage should not exceed 3.2 grams/day.
Oxycodone with acetaminophen (Percocet, Tylox, Roxicet). This drug combination is used to manage moderate to severe pain in patients with photokeratitis. The usual dosage is 1-2 tablets or capsules by mouth every 4-6 hours, while the symptoms persist.

Ophthalmic analgesics are pain medications whose effects are localized to the eye. Some ophthalmologists prefer to use ophthalmic analgesics instead of systemic analgesics to manage pain associated with ultraviolet keratitis. These topical analgesics have been shown to relieve pain in multiple situations, including corneal abrasions, allergies, and post-surgical pain.

Ketorolac tromethamine 0.5% (Acular) both treats pain and inflammation associated with corneal flash burns. A typical dose is one drop into each affected eye four times per day, while symptoms persist. This regimen should not exceed two weeks.
Diclofenac ophthalmic (Voltaren) both treats pain and inflammation associated with corneal flash burns. A typical dose is one drop into each affected eye four times per day, while symptoms persist. This regimen should not exceed two weeks.

Recommended dosages listed above are for adults. Your ophthalmologist will make the proper adjustments for administering them to children, when indicated, for treatment of corneal flash burns.

It is essential to remember that the single most important thing that you can do to prevent ultraviolet keratitis is to wear protective eye wear that blocks the largest portion of UV radiation possible when engaged in activities that place you at risk for developing corneal flash burns. It is not recommended to view a solar eclipse directly even if you are wearing protection from ultraviolet waves. If you begin to show symptoms of photokeratitis, see an ophthalmologist immediately.

REFERENCE:

Krachmer JH, Mannis MJ, and Holland, EJ. Cornea: Fundamentals of Diagnosis and Treatment, 3rd Ed. New York: Mosby Elsevier, 2011.

McIntosh SE, Guercio B, Tabin GC, Leemon D, Schimelpfenig T. Ultraviolet keratitis among mountaineers and outdoor recreationalists. Wilderness and Environmental Medicine. 2011;22(2):144-147

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