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Vision problems The eye works like a camera. Just as a lens
will focus light onto the film at the back of the camera, your cornea and lens,
located behind the pupil, act together to focus light rays onto the retina at
the back of the eye. The retina acts like the film in the camera by converting
light into nerve impulses. These signals travel along the optic nerve and back
to the brain which interprets them for vision.
Four types of optical focusing or refractive errors are commonplace,
especially as people age: Optical correction optionsSpectacles and contact lenses are excellent and safe methods for correcting focusing problems for most patients. If a large correction prescription is required, glass lenses may need to be thick and cause distortion which may be uncomfortable. Certain jobs, such as airplane pilots, boat captains, policemen, and firemen, require good vision without glasses.Hard and soft contact lenses fit directly on the cornea to correct vision. Contact
lenses are worn comfortably by most patients as long as there are no corneal
diseases, eyelid problems, or dry eye conditions. Some patients initially do
well with contact lenses but subsequently develop irritation due to allergies or
prolonged use.
One option to reduce the effects of presbyopia is called monovision. In
monovision, one eye is fully corrected for distance vision. The other eye is
left with a low level of nearsightedness. This allows ability to read
without glasses. Although millions of individuals successfully utilize monovision to eliminate use of distance and reading glasses, not all individuals can adapt to monovision.
Screen fatiqueThere is no convincing scientific evidence that computer monitors or video display terminals are harmful to your eyes. However, complaints of eye discomfort and fatigue are common as computer use increases.VDTs and your vision
Extensive testing in government laboratories has established that VDTs and LCD monitors emit little or no harmful ionizing radiation (such as X-ray) or non-ionizing radiation (such as ultraviolet) under normal operating conditions. In fact, the amount of ultraviolet radiation produced by VDTs is a small fraction of that produced by fluorescent lighting. The levels of radiation from VDTs are well below those required to produce cataracts or other eye damage even after a lifetime of exposure. Some people will temporarily notice that black and white objects appear tinged with color after viewing VDTs for an hour or more (this is called the McCollough Effect). These colors are usually complimentary (opposite) to the color of the VDT characters, and are not a sign of an eye disease, damage to the eye, or eye strain. Can VDTs be associated with eye strain?Use of computer monitors is associated with eyestrain. You may notice a variety of symptoms
including eye irritation (red, watery or dry eyes), fatigue (tired, aching
heaviness of the eyelids or forehead), and difficulty focusing. Headaches,
backaches, or muscle spasms can also occur. These complaints can often be
relieved by either changing the arrangement of the workstation or providing
proper glasses for the user. Use of computer monitors often results in a decreased blink rate, which causes dryness, tiredness, and secondary watering of the eyes. Frequent blinking and artificial tears will usuallly help to lubricate the eyes and alleviate these symptoms. It may be helpful to lower the monitor height if possible since this allows less exposure of the surface of the eye to the air, since the upper lid can be at a lower level. What are the special vision needs of VDT users?The VDT screen must be kept in proper focus. Since the screen is usually placed farther away and higher than the usual reading distance, different glasses may be necessary. This is especially true for individuals who wear bifocals, trifocals or reading glasses. A bifocal height may need to be raised to compensate for the higher positioning of the VDT. The additional visual demands of VDT use may mean that some individuals who normally do not need glasses should have corrective lenses for this activity. Your ophthalmologist can prescribe the correct glasses for you. You will need to describe the layout and dimensions of your workstation for the ophthalmologist to calculate the lens power that will work best for you. In addition, the comprehensive medical eye examination you receive from your ophthalmologist will help diagnose whether the discomfort you experience with VDT use is due to simple eyestrain or whether unsuspected disease is present. Source: American Academy of Ophthalmology |
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A
nearsighted eye is usually longer than a normal eye. In a myopic eye, light rays
come into focus in front of the retina. As a result, a myopic patient can see
close objects, but objects in the distance are blurred. Myopia is often an
inherited condition. Symptoms usually appear in childhood or early teenage years
and stabilizes in the twenties.
A
farsighted or hyperopic eye is usually shorter than a normal eye. This is the opposite of
near-sightedness or myopia. Light is not brought into focus before encountering the retina.
Depending upon the amount of farsightedness, a patient may experience little or
no blur in the distance, but will have increasingly blurry vision for close
objects. Reading glasses are sometimes required for hyperopia as a child or young adult, but often are not required until reading becomes difficult in middle age.