EYE STRAIN

Ophthalmologist Carolina Valdivia, MD discusses causes and symptoms of eye strain and what you can do to prevent it.

Asthenopia symptoms are not present when you wake up, but occur throughout the day and often become worse as the day progresses. They primarily are due to muscle fatigue.

WHY DO MY EYES ACHE?

Through a mechanism called accommodation, the eye is able to focus on images at different distances. Inside the eye there is an array of fibrous ligaments known as the Zonules of Zinn that suspend the lens of the eye in front of the pupil. The Zonules of Zinn are connected to a muscle called the ciliary muscle. When the ciliary muscle is relaxed, the Zonules of Zinn are stretched into a taught configuration and the lens flattens. This enables us to focus on things at a distance. Conversely, when the ciliary muscle contracts, the Zonules of Zinn are in a relaxed configuration, which causes the lens to curve and thicken. This allows us to see images up close with clarity.

You can illustrate this fatigue by placing an average-size book in the palm of your hand, and then extend your arm out away from your body and hold it there. While it might seem like an easy task at first, over time the muscles in your arm will become tired. Eventually you will feel so much discomfort that you will have no choice but to relax your arm.

In a similar manner, the ciliary muscle can be overworked. Couple this with inadequate sleep, which deprives the ciliary muscle of an opportunity to properly recover, and you can have chronic eye strain. Allowing the ciliary muscle to relax during the day by focusing on a distant object at least once an hour and getting adequate sleep usually alleviates the asthenopia problem.

WHAT CAUSES EYE STRAIN?

Primary causes of asthenopia include:

• Refractive errors in the eye. These problems occur when visual information is not focused properly on the retina. Instead, the point of focus occurs in front of the retina (nearsightedness) or behind the retina (farsightedness). Eye strain results because the eye attempts to make adjustments through accomodation, which again overworks the ciliary muscle and other muscles of the eye. An evaluation by an eye-care professional will determine if your asthenopia is caused by refractive errors in the eye. If yes, the use of corrective lenses will resolve this problem and provide better visual acuity.
• Focusing on a fixed object for prolonged periods. Our eyes are structured to shift focus between near and distant objects. This shifting provides an opportunity for the ciliary muscles of the eye to relax after contracting. Extended focusing on a single object does not provide ciliary muscle relief and can cause eye strain. Eyes are strained by close viewing more than by distant viewing.
• Different distances between close points of focus. You can experience asthenopia if you frequently shift between two objects that are close, but located at different focus distances. Examples include working on a computer while watching television, switching between reading printed material and a computer screen, watching television while doing needle work, and switching between reading two or more sources of printed material that are placed at different distances from your eyes.
• Poor lighting. Doing close work in poor light forces your eyes to focus under difficult conditions.
• Contrast. This is the difference in brightness between what is being viewed and its immediate environment. Excessive contrast can lead to eye strain. This may occur if a dark screen is surrounded by a bright background such as a window or a lighted wall, or if a screen shows light text on a dark background.
• Glare. Direct glare occurs when a light source shines into the eyes. Examples include unshaded lamps, bright ceiling lights, bright sunshine entering through a window, and bright outdoor sunlight. Reflected glare occurs when reflections from surfaces reduce visibility or create discomfort. This is because the contrast between the image you are viewing and its background is reduced by the reflected light, making it harder for your brain to interpret the image. As your eyes strain, facial and eye muscles tighten.

These causes usually do not occur separately. More frequently they are present in various combinations.

SYMPTOMS OF EYE STRAIN

The following symptoms are associated with asthenopia.

• Headaches
• Eye pain
• Eye redness
• Watery eyes
• Dry eyes that feel scratchy
• Burning sensation upon closing the eyes
• Twitching in the eyelid
• Aching eyelids or forehead, especially around the eyebrows
• Spasms in the muscles surrounding the eyes
• Blurred or double vision
• Back aches and neck aches

WHO IS AT RISK?

Asthenopia typically occurs in people who do close-up work, read a lot, or spend long periods watching television or using a computer. Visual problems, such as eye strain and irritation, are among the most frequently reported complaints from computer users.

RELIEVING AND PREVENTING EYE STRAIN

In most cases, asthenopia does not mean that you will have long-term or permanent eye damage. However, it is important that you identify the cause of your eye strain and correct it in order to relieve your symptoms. The following strategies should help you.

• Visit an eye-care professional for an eye examination to see if you need corrective lenses and to exclude the possibility of an eye disease or disorder.
• If you already wear corrective lenses, have your vision tested to make sure that your prescription is correct.
• Children with uncorrected refractive disorders often sit close to the television screen or hold a book close to their eyes in order to see more clearly. An ophthalmologist can diagnose these conditions and prescribe corrective lenses.
• When reading, knitting or drawing, hold your material about 30 to 40 cm away from your eyes. Ensure you have adequate soft light (a 60 to 100-watt bulb) behind you.
• If you will be driving for an extended period, stop every few hours to rest your eyes and stretch your muscles.
• Take vision breaks every 30-60 minutes to relax your eye muscles. Try closing your eyes and relaxing for one minute. Other useful exercises may include rolling or blinking your eyes, or closing them tightly for a few seconds.
• Changing focus is another way to relieve the eye muscles. Every 15 to 30 minutes, look across the room or out of the window at an object at least 6 m away, for at least 20 seconds.
• If more than one close-up focus area is needed, such as using printed reference material and a computer screen simultaneously, keep the viewed objects at the same distance and as close to each other as possible. This helps to reduce focusing changes.
• Ensure that close-up work or a computer screen is not too close to your eyes. As a general rule, view material from as great a distance as possible, provided it can still be read easily.
• Workstations and lighting should be arranged to avoid direct and reflected glare anywhere in your field of vision. Place the computer or television screen where there is no glare from windows or lights and keep screens clean and dust-free. Use a glare filter on the screen if lighting cannot be modified.
• Wear sunglasses that reduce glare and provide 100% protection from ultraviolet rays while you are outside, especially on bright or hazy days. Sunglasses also prevent squinting that may strain eye and facial muscles.
• When using a computer or similar equipment, room lighting should not be as bright as the screen. To reduce troublesome contrast, find a way to darken the area around the screen. Keep your computer monitor in proper focus.
• While you are watching television, the room lighting should be about 50% dimmer than the screen. Do not watch in darkness because this makes the contrast in light too great. Avoid viewing from an angle and sit at a reasonable distance from the Television (about four or five times the width of the screen). In other words, for a 50-cm screen, sit about 2 to 2.5 m away. People with poorer sight may need to sit closer.
• Position the top of your computer monitor or television screen at (or slightly below) eye level so you look downwards at it. This can help with dry eyes. More of the eye surface is covered by the eyelid when you look down, with the result that your eyes blink more and produce more lubrication.

Resting your eyes often relieves eye strain. However, symptoms of asthenopia also can be an indication of something more serious. If you suffer prolonged discomfort or notice a change in your vision, make an appointment to see an ophthalmologist without delay. An ophthalmologist is a medical doctor that specializes in the eye. She or he will be in the best position to diagnose your problem.

REFERENCE:

Crick RP and Khaw PT. A Textbook of Clinical Ophthalmology, 3rd Ed. River Edge, NJ: World Scientific Publishing Co. Pte. Ltd, 2003:51-76.

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