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Glossary of Terms

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Terms on this page


Print this definitionAccommodative Excess

Accommodative Excess refers to the tendency to focus closer in than the page being read, ie the individual will focus as if the book is closer than it really is.

This is commonly found in cases of Convergence Insufficiency, where the individual has difficulty aiming the eyes at near at the same place on the page, by overfocusing the eyes are able to be brought together to the one point.

Accommodative Excess however reduces visual stamina and can affect binocular vision.

In school aged children this is of concern as it both reduces visual efficiency but also delays ability to shift focus between distance and near tasks.

It is common in these cases for symptoms of headaches and/or sore eyes to be reported.

In cases of Accommodative Excess, there is often the report of transient blur in the distance when looking up after doing near tasks such as reading.

The risk factor is myopia (shortsightedness) being induced later in life, often in the teenage years, should accommodative excess be allowed to continue.

Treatment is the use of a Therapuetic spectacle lens prescription, this usually prescribed as a multifocal lens. The concept being to utilise the bottom section of the lens to improve near binocular vision levels whilst still allowing clear distance vision through the top of the lens, this being especially important at school and university.

Also in some cases Vision Therapy may be indicated to retrain the visual system to operate in a more efficient manner.

Print this definitionAccommodative Insufficiency

Accommodative Insufficiency refers to a reduced level of focus stamina required for accurate near binocular vision.

This is often associated with a Convergence Excess, reduced levels of accommodation often requiring the individual to aim the eyes closer in than the page they are reading in an effort to increase focus strength.

Insufficient accommodation usually results from either delayed vision development in children, or in situations of visual stress in adolescents and adults.

Treatment for accommodative insufficiency is best addressed by use of Therapuetic Spectacle lenses. These are generally prescribed in a multifocal form to allow improved near vision accuracy whilst not disturbing distance vision, this being especially important in school children so they may shift focus with ease and clarity between board and page in class.

Accommodative Insufficiency can reduce visual attention levels and visual memory abilities as the child is required to direct more attention to keeping clear vision, thereby reducing available concentration required for processing the visual information.

Often stamina and ability to concentrate in class or at work is affected, and the individual finds it difficult to keep focus on the page, often looking away or daydreaming. It is common to find these individuals having to re-read sentences over again for comprehension.

The Behavioural Optometrist is able to accurately assess levels of accommodation and prescribe appropriate treatment should this be required.

Print this definitionAmblyopia

Amblyopia, or lazy eye, is poor vision in an eye that failed to develop normal vision during early childhood.

It affects around 2 to 3 percent of people. Someone with amblyopia usually has good vision in one eye, although it is possible for amblyopia to develop in both eyes.

Any condition that impedes the normal development of vision in an eye can cause amblyopia, however the two most likely causes are:

  • Strabismus (misaligned or crossed eyes) - A misaligned or crossed eye will eventually turn-off to avoid double vision occurring. This will prevent vision from developing normally and amblyopia will result.
  • Unequal Focusing - Amblyopia can occur in an eye that has poorer focusing than the other eye due to refractive error. This can be difficult to detect as there is no visible symptom like in the case of a crossed eye.
  • Non-refractive Amblyopia - May occur in the absence of poor focusing or an eye turn yet one or both of the eyes may have blurred vision. This is commonly associated with some form of congenital developmental delay, or may be associated with an eye injury or brain injury.

Amblyopia may also develop in an eye that has become cloudy in the areas of tissue that are normally clear. An example of that is Cataracts.

Where a child has high levels of long sightedness, shortsightedness or astigmatism, amblyopia may develop in both eyes.
Because amblyopia is not easily detectable in infants, a routine eye examination by an optometrist is recommended for all small children. The earlier amblyopia is diagnosed, the more effective the treatment will be.

Ideally, treatment for amblyopia should begin in infancy or early childhood.

Amblyopia is treated by wearing glasses to improve the vision in the poor eye, thus allowing the vision to develop normally. In some cases the good eye may be blurred with the use of glasses or a patch to encourage the poorer eye to work. Vision Therapy is often very effective in the treatment of amblyopia, this involves a customised program of activities conducted both in-office and at home in order to stimulate the visual system and enhance binocular vision ability.

Success in treating amblyopia depends on how severe it is and how early it's detected. Early detection and treatment of amblyopia will mostly result in improved vision.

Print this definitionAnisometropia

Anisometropia is a significant imbalance in refractive error between the eyes.

That is one of the eyes requires a significantly stronger corrective prescription in order to see clearly.

This is commonly found in Refractive Amblyopia, ie where one of the eyes is either not used fully compared to the other eye due to an excessively high prescription, or where one of the eyes appears initially to not function correctly.

Treatment for anisometropia is usually the corrective spectacle prescription to give maximal visual acuity for each eye. This is important to reduce the risk of Amblyopia in cases of untreated anisometropia. Vision Therapy may be useful in treating the effects of anisometropia.

Print this definitionAstigmatism

Astigmatism results when the shape of the cornea (the clear section of the eye covering the iris) is not spherical; in other words, when the cornea is shaped more like the back of a dessert spoon rather than the back of a soup spoon. It may also exist, although less commonly, because of an irregular shaped lens within the eye.

Astigmatism is not a disease; it is merely a variation in the shape of the cornea or lens and is very common. It should be noted that in cases of continual progression of astigmatism, there is a need to exclude Keratoconus, which is a disease of the collagen fibres of the cornea, often genetic, that allows progression of a cone shaped cornea. This is best measured using a Corneal Topographer, which is available at Vision West, and treated using Rigid Gas Permeable Contact Lenses.

Moderate to large amounts of astigmatism will cause images to appear misshapen and blurry at any distance.

The usual way of correcting astigmatism is by wearing glasses or contact lenses. Most long sighted, short sighted and presbyopic people will also have small amounts of astigmatism which the optometrist will account for in a spectacle correction.

In children it is possible to measure a type of astigmatism that is actually secondary to focusing conditions, ie the eye shape may be correct but astigmatism is measured. This is best treated using behavioural optometry techniques including therapeutic spectacles and/or Vision Therapy.

There also exists lenticular astigmatism where the lens shape is irregular, again causing distortion of incident light. 

 

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Word of the Moment

Myopia (short-sightedness)
Where the length of the eyeball is greater than the focus power of the eye, hence blurred images are presented to the retina giving reduced vision. Known as Myopia, Nearsightedness or Shortsightedness. more