Monday, June 15, 2009

Fried eyes

Fried eyes

Mon, Jun 15, 2009
The Star/Asia News Network

By Lee Tse Ling

MANY of us know excessive exposure to ultra-violet (UV) light is hazardous, but only associate harmful effects with skin disorders, most commonly with sunburn, premature aging, and cancer, and perhaps less commonly with sun allergies, systemic erythematosus lupus, and pre-cancerous growths/lesions.

Falling somewhere in between the two is the awareness that UV light can cause long-term damage to sight.

What is UV light?

Natural UV light is a component of sunlight - a combination of UVA, UVB, and UVC rays that's invisible to the human eye.

UVC rays are blocked by the ozone layer. UVA rays make up 90% of UV light that reaches earth. They give you a suntan, but also penetrate deeply into the eye, hitting the retina (the light-detecting layer of the eye). UVB rays make up 10% and are nastier. They cause sunburn and cancer, and are absorbed by the cornea (the clear layer in front of the eyeball) and lens (the bit that focuses light on the retina).

Interestingly, UV light is visible to some birds and all bees. Raptors like eagles and falcons can track prey whose urine absorbs UV light, leaving a visible trail to follow. Bees are directed to nectar by plants displaying UV markings on their flowers.

So UV light has an important role to play in the natural world. For us, too much can cause the eye- and sight-related disorders below, cautions consultant ophthalmologist Dr Linda Teoh.

Cataracts: A cataract is a clouding of the lens inside the eye, which can scatter light entering the eye irregularly, or block it altogether, resulting in blurry vision, shortsightedness, photosensitivity, or blindness.

They are a major cause of visual impairment worldwide, but are preventable, treatable (surgical removal), and the blindness they cause is usually reversible.

"It's not a disease, it's an ageing process that occurs in the eye," Dr Teoh reassures. Consult your physician early, even if your cataract is not disabling, as it may conceal other eye problems. To prevent them, Dr Teoh recommends UV-blocking eyewear, vitamin supplements, quitting smoking, and controlling blood sugar levels (uncontrolled blood sugar levels, eg in diabetics, can accelerate cataract development).

Age-related macular degeneration (AMD): AMD occurs when the cells of your macula (the part of your retina that registers the sharpest images) die. This destroys sharp central vision, as if someone has smudged out the middle of your field of vision. A person with AMD can see hazy peripheral outlines, but not fine details necessary for, say, reading and driving safely.

There are two forms: dry AMD progresses slowly with age, wet AMD progresses quickly due to blood vessels growing abnormally under the macula, which displace it. Both are painless, and easy to ignore or accept with a resigned sigh as part of "growing old". Don't. It's one of the leading causes of chronic blindness worldwide.

While controllable risk factors include smoking, being obese, and exposure to UV light, age is the greatest risk factor. So from 60 onwards especially, see an ophthalmologist if you develop blurry vision (eg have difficulty recognising faces or words on a page) that may improve in brighter light; a small, growing blind spot in the middle of your field of vision; or if straight lines appear crooked to you.

Pterygium: A non-cancerous growth on the white of the eye that extends onto the cornea that can block or distort vision, and cause irritation (eg itching, burning, or a "gritty" feeling). More often it is painless, but may be considered unsightly, and so be surgically removed (note: it tends to recur).

It's seen most often in adults who work outdoors, exposed to sun and wind. Untreated, it can cause vision loss.

Photokeratitis: A.k.a. corneal sunburn, caused by excessive UVB exposure eg from too much time spent on a sunny beach without eye protection. Symptoms may not appear until six or more hours after exposure, last one to two days, and include very sore, bloodshot, and teary eyes; blurry vision or temporary vision loss; and photosensitivity. Treatment consists of symptomatic relief.

Preventing UV damage

When it comes to your eyes, an ounce of prevention is definitely worth a pound of cure:

  • Ensure all eyewear provides 100% UVA and UVB blockage. Check that it comes with a World Council of Optometry seal of acceptance for UV blockers/absorbers.
  • Consider wraparound sunglasses, larger frames and/or side panels for added protection.
  • Wear a hat/cap (minimum brim width: 8cm) outdoors.
  • Seek shade, especially from 10am to 3pm.
  • Take extra care when UV exposure is enhanced ie when light is reflected off pavements, water, sand, and snow.
  • Be aware of UV risk wherever you go. Get a seven-day solar UV Index (UVI) forecast of locations around the world at (the World Health Organisation- established UVI runs from 0: Low to >11:Extreme).
  • Protect children's eyes as early as possible. Kids spend more time outdoors, may not remember to protect themselves, and are more vulnerable (the immature lenses of children under 10 block just 25% compared to 90% in adults aged 30). Studies have also shown higher UV exposure in teenagers and young adults is linked to a higher risk of developing cataracts and AMD later on.

The Star/Asia News Network

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