Experts answer vital questions on lighting, dry eyes, vision, computer use and exercises.

Can reading in dim light damage your eyes?
"I remember my mother coming into my room and telling me that 'reading in the dark is bad for your eyes'," says Professor David Mackey, of the Lions Eye Institute.

"I replied that it isn't and I'm an ophthalmology professor. If your eyes aren't in good focus then poor lighting makes it more difficult to read.

"Most people who wear reading glasses can manage outside in bright light but find it hard in dim lighting and therefore need to wear glasses. It is an effect, not a cause."

What causes dry eyes?
Healthy eyes should have a thin film of tears at all times, keeping the eyes from becoming dry and keeping vision clear.

But particularly for many older people, dry-eye syndrome - properly called keratoconjunctivitis sicca - can leave eyes stinging or burning, making them more sensitive to wind and light and feeling uncomfortable or tired.

The respected Mayo Clinic says the condition can affect anyone but is more common with age and in post-menopausal women.

There are medical conditions that also appear to increase the incidence, such as diabetes, rheumatoid arthritis and lupus, as can medications such as the pill, antihistamines or some blood pressure drugs.

Using eye drops known as artificial tears can help lubricate dry eyes but if they don't relieve the symptom it is worth speaking to an ophthalmologist or optometrist about alternative treatments.

What does it mean to have 20/20 vision?
There are different ways to describe visual acuity but the term 20/20 vision is a commonly used term to describe the vision of a normal person.

It relates to the Snellen Eye Chart, and someone with 20/20 vision should be able to read the eighth line on the 11-line chart from a distance of 20 feet (with the lower figure relating to distance and visual angle of the lines of letters).

In Australia, normal vision is also referred to as 6/6, (converting 20ft to 6m). The smaller the bottom figure is, the better the person's vision.

What are the limits of human eyesight?
While 20/20 might be considered "normal", the average of healthy eyes is slightly better, estimated about 20/16, which - in rough terms - means someone can see at 20 feet what someone with normal vision would need to be at 16ft to see.

In Australia, a person is considered legally blind when their vision wearing correction aids is no better than 6/60 or 20/200.

American researchers investigating the eyesight of almost 400 professional baseball players have reported that 77 per cent have 20/15 vision or better.

The best reading recorded was 20/9, but it may be that some of this visual acuity relates to a better ability to interpret and make sense of blurred objects.

A Melbourne researcher in the 1970s recorded visual acuity at 20/10 among several Aboriginal people in remote communities.

Does using a computer cause poor eyesight?
For children or adults who have a slight turn in their eye or for whom the screen is out of focus, near work on a computer can be fatiguing, says Professor Mackey.

Thus if you plan to spend a long time on the computer, it's good to have a check-up to see if glasses might help.

Data suggests that a lot of near work may lead to myopia (short-sightedness) in adolescents, although the Sydney Myopia Study indicated that it's the lack of time spent outdoors that's more likely the factor involved.

How can you tell if a young child has a vision problem?
Children can often try to adapt to poor eyesight rather than report it as a problem, so if you think there might be a problem, you should always see an optometrist for a check.

Even if they are unable to recognise letters on an eye chart, there are charts designed for people who cannot read or who are very young.

The Optometrists Association Australia recommends parents look for signs that could indicate a possible problem, including one eye that turns in or out while the other looks straight ahead, frequent blinking, red or watery eyes, difficulty concentrating, covering or closing one eye, holding books very close, squinting or sitting very close when watching television, and any complaints of headaches, blurred or double vision.

Can eye exercises help someone with a strabismus?
The short answer is no, says WA orthoptist Amy Crosby. But occasionally they can help, particularly if a person has a strabismus only when they are focusing at a certain distance, and are straight the rest of the time.

Exercises can teach someone to recognise when their eye or eyes are turning and how they need to change their vision to straighten their eyes.

For example, some people who are long-sighted can have an eye turn in when they look at something close up as they focus to make it clear. Sometimes, if that person allows the object to be slightly blurred, they can keep their eyes straight. If they can't do this, they may need glasses or surgery. It will pay to see an ophthalmologist.

Exercises may help in a condition called "convergence insufficiency" when a person's eyes can become fatigued after long periods of reading or similar close work.

The usual treatment for this can be reading glasses but sometimes working through a series of exercises at home and with an orthoptist can help strengthen the eyes.

The West Australian

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