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Glossary of Terms

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Print this definitionCataracts

A cataract is a cloudiness that develops in the normally clear lens in the eye. The effects of cataracts can best be explained as similar to looking through a misty window. Over time a cataract will become denser and denser until it occludes vision altogether.

There are several causes of cataracts, the most common being associated with ageing (Age Related Cataracts). Although cataracts don't usually start to affect most Australians until they are in their 60's or 70's, an earlier onset of cataracts can be attributed to smoking, excessive exposure to sunlight, diabetes, and the long term use of some medications (Secondary Cataracts). Cataracts may also develop after an eye injury (Traumatic Cataracts) and in rare cases babies are born with cataracts or develop them in early childhood (Congenital Cataracts).

As cataracts usually develop slowly over a long period of time, most people only become aware they have them following a routine visit to the optometrist or ophthalmologist. Someone with cataracts may need to have several prescription updates over a shorter than normal period of time.

Common symptoms of cataracts are:

  • Cloudy or blurred vision at any viewing distance
  • Glare sensitivity
  • Haloes around lights at night time
  • Colours looked washed-out

Cataracts are treated by way of a surgical procedure performed by an ophthalmologist in a hospital or day surgery. Sophisticated equipment assists the ophthalmologist to perform suture-less surgery that removes the cataract portion of the lens, which is then replaced with an artificial prosthetic lens.

Prior to the surgery, measurements are taken and calculations are made to ascertain the type of prosthesis that will be used to deliver as close as possible to clear distance vision without the need for glasses. Some pre existing conditions such as astigmatism may not be fully corrected during the surgery and glasses may still need to be prescribed. In most cases reading glasses will be needed after cataract surgery, and in many cases multifocal spectacles are still the ideal option for practicality.

Print this definitionConvergence Excess

Convergence Excess occurs where the natural posture of the eyes is closer in than required for near vision tasks.

Convergence excess means the individual, when they look to near vision tasks, has a natural tendency to aim the eyes closer in than the position they are trying to aim at.

For example someone reading would ideally aim and focus the eyes together on the words on the page, in cases of convergence excess there is usually the situation where the eyes meet to aim at a point closer in than the page.

Often individuals can be noted to work closer to the page when this occurs.

This excess of vergence is commonly associated with an Accommodative Insufficiency. The eyes are aimed closer in than desired in an attempt to compensate for reduced focus stamina or focus ability.

This leads to a mismatch between vergence and focus, thus affecting binocular vision accuracy.

Management of convergence excess requires therapeutic spectacle prescription lenses to enhance the focus efficiency thus reducing the need to pull the eyes closer in.

This is a therapeutic treatment that requires monitoring over time to ensure the excessive demand is reduced to within a normal range of focus and convergence.

Usually over time prescriptions can be reduced and wearing time reduced.

Without effective management, myopia (shortsightedness) can often result in later years, such as in high school.

Print this definitionConvergence Insufficiency

Convergence Insufficiency is a reduced ability to bring the eyes together for near vision tasks.

In order to read and focus at near, the visual system is required to make a single clear image by bringing the eyes closer together, this usually being stimulated when a person looks down and close. If this does not occur then a blurred double image would be the result, or the brain would switch one eye off to cope, this is termed Suppression or Amblyopia.

In many cases the reduced ability to bring the eyes together for near vision tasks is related to focus insufficiency. That is, many children have reduced convergence being linked to inefficient focus for near vision affecting awareness of where to aim the eyes, this due to developmental delay in their focus stamina.

In cases of focus issues being linked to the convergence insufficiency, therapeutic spectacle lenses are often all that is required to improve both the focus delay and convergence ability.

These Therapeutic spectacle prescriptions are most commonly dispensed in multifocal form, so that assistance may be given for near vision without disturbing distance vision. This is necessary in a classroom situation for children or office situation for an adult so as to allow smooth transition of focus between distance and near tasks.

Usually single vision lenses, although beneficial for near, become problematic in the distance as the individual is then looking through a prescription they do not require when trying to look at the blackboard. So benefit at near can be negated by the distance blur, leading to further eyestrain and compliance issues.

In cases of convergence insufficiency which are more related to the ability of the visual system to turn the eyes inward then a program of Vision Therapy may be required to retrain the eye muscles to converge. This is usually due to a developmental delay in the flexibility, co-ordination and integration of the eye muscles that move the eyes in whichever direction we are to be looking.

In more longterm cases of convergence insufficiency, it is common to find an Exotropia also being present, where one eye fixates and the other remains slightly divergent, ie an outward eye turn.

Often a combination of Vision Therapy and Therapeutic Spectacle Prescriptions are required to manage cases of Convergence Insufficiency.


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Word of the Moment

Orthokeratology more commonly referred to as ‘Ortho-K', the use of contact lenses to reshape the cornea (front surface of the eyes) in order to reduce levels of myopia and astigmatism. The lenses are worn in the evening whilst sleeping and allow clear vision for the next day once removed upon waking. more