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Vision Disorders

Refractive errors cause decreased vision, visual discomfort ("eye strain"), and/or
amblyopia. The most common form, nearsightedness (poor distance vision) is
usually seen in school-age children and is treated effectively, in most cases, with
glasses. Farsightedness can cause problems with focusing at near and may be
treated with glasses. Astigmatism (imperfect curvature of the front surfaces of
the eye) also requires corrective lenses if it produces blurred vision or discomfort.
Uncorrected refractive errors can cause amblyopia particularly if they are severe
or are different between the two eyes.

Below are a few conditions discussed briefly.

Myopia
In cases of mild or moderate myopia (short-sightedness) there is the ability to
see close objects more clearly than distant objects, which, without glasses, would
appear blurred. With more severe myopia, vision is more likely to be slightly
impaired even with correct glasses. Strong lenses are needed to make the image
even smaller and, in some cases, vision may be better with contact lenses. A
feature of non-myopia reduced vision is that many with a visual disorder will
see objects close to them and be inattentive to those more distant. It is,
therefore, not helpful to prescribe the same type of glasses as those used
with myopia.

Farsightedness, or hyperopia,

as it is medically termed, is a vision condition in which distant objects are
usually seen clearly, but close ones do not come into proper focus. In mild
cases of farsightedness, your eyes may have been able to compensate
without corrective lenses.

A person with hyperopia is able to see objects at a distance, but has trouble
with objects up close, like books or newspapers. Many people are not
diagnosed with hyperopia without a complete eye exam.

Farsightedness occurs if your eyeball is too short or the cornea has too little
curvature, so light entering your eye is not focused correctly. The cornea and
the lens work together to focus images from the visual world on the back of
the eye (the retina). If an image is out of focus, it is typically because the
overall shape of the eye is incorrect or the cornea does not have the proper
curvature.

Farsightedness or hyperopia occurs when the eye is too small or the cornea
is too flat. When this happens, visual images are focused behind the retina.

Squint
Squint (misalignment of the eye/s) is incompatible with normal stereo acuity if
constantly present. Vision function may however be normal in other ways and
surgical straightening of the eyes will not benefit any other vision functions.
Squint may co-exist with other vision problems but is often the consequence,
and not the cause, of these problems.

Amblyopia
The term 'lazy eye' is often used instead of the more correct term of amblyopia.
It results from poor development of brain cells and connections in the vision
areas of the brain during maturation of the visual pathways. This is because
the brain ignores fine detail vision of one eye that is misaligned (squint), is not
focussed (needing glasses), or is closed or obscured by, for example, a cataract.
This can only be treated when the brain pathways are still plastic (maturing and
changeable) by covering the 'good' eye for certain periods of time thereby forcing
the brain to use the 'lazy eye.'

ASTIGMATISM
Astigmatism occurs when the front surface of your eye (cornea) is slightly
irregular in shape, resulting in vision being blurred at all distances.

In Astigmatism, the front of your eye is more oval than round, light does not
focus properly on the back of your eye (retina).

The causes of this irregular shape are unclear. In some cases, it may be
hereditary or it may result from such factors as pressure of the eyelids on
the cornea, incorrect posture or an increased use of the eyes for close work.

Corneal dystrophies
The front of the eye is usually clear but clouding may occur as an isolated
problem or as part of a more generalized disorder. This results in reduced
vision, amblyopia and photophobia (discomfort and dazzle in bright light).
Occasionally fragility of the cornea surface and recurrent sore eyes occur
due to spontaneous erosions.

PRESBYOPIA

As we age, body tissues normally lose their elasticity. As the lenses in our
eyes lose some of their elasticity, they lose some of their ability to change
focus for different distances. The loss is gradual. Long before we become
aware that seeing close up is becoming more difficult, the lenses in our eyes
have begun losing their ability to flatten and thicken. Only when the loss of
elasticity impairs our vision to a noticeable degree do we recognize the change.

With presbyopia the crystalline lens of your eye loses its flexibility, which makes
it difficult for you to focus on close objects. Presbyopia may seem to occur
suddenly, but the actual loss of flexibility takes place over a number of years.

Retinal Dystrophy
The retina 'takes the picture' and processes an image to send as a signal to
the brain. Some children are born with a malformed (dysplastic) retina but
as it cannot be replaced (transplanted) this cannot be treated.

Retinal detachment
If the retina of the eye becomes displaced it is like taking the film out a camera
and not being able to take a picture. Some eye conditions have a high risk of
retinal detachment but in some cases the retina can be reattached by surgery.
The chances of success are higher the sooner after detachment this is performed.