General EYE ADVICE

The Importance of Detecting Astigmatism

Detection of astigmatism, especially in pre-schoolers, is particularly important for a number of reasons. Astigmatism does not usually cause as much blurred vision for distance viewing as myopia can. However, unlike myopia, astigmatism also affects near vision to about the same extent as it affects distance vision. In the modern day environment, where near work is of particular cultural importance, astigmatism can be an important obstacle in preventing clear and comfortable near vision. This in turn can lead to other problems, including sub-optimal performance in reading and studying. Astigmatism can also be an important factor in the development of myopia and may also lead to postural changes when close work is attempted. These positional changes of the head may have long-term effects on the spine. (See Part I, Section B for further discussion on astigmatism and near work).

As children with astigmatism do not usually have a severe sight problem (unless there is a coexisting myopia etc), their behaviour is not obviously suggestive of a vision problem and parents are often unaware of the presence of astigmatism. Adults can often overcome milder amounts of astigmatism for several years without significant symptoms, until faced with highly demanding tasks. An eye examination by a qualified eyecare practitioner, who will also measure any vision defect and the shape of the cornea of the eye, is the best way to detect the presence of astigmatism.

The cornea is the major refracting surface of the eye. It is normally only mildly warped i.e."astigmatic", and this is overcome by a tonic focusing of the lens within the eye, resulting in normal vision. If for whatever reason, during the development of the eye, the cornea is allowed to be significantly warped, the eye will usually be affected by astigmatism. This is because the eye is usually incapable of focusing for higher degrees of corneal "astigmatism", except in some cases.

In these latter cases, the structures within the eye appear to allow the lens to accommodate for, or neutralise the corneal "astigmatism". The vision in these eyes is usually normal and if the corneal curvature is not measured, the practitioner usually cannot find any astigmatism of the eye. However, as a greater amount of continual focusing is required in these cases, the patient may experience eyestrain symptoms. Blurred vision may result if the eyes can no longer continue to focus and corneal "astigmatism" becomes manifest as astigmatism of the eye. This condition is termed "latent astigmatism" to denote that it is possible for astigmatism of the eye to surface at a later time.

Apart from eyestrain symptoms, latent astigmatism has been proven to be associated with increased myopia. (Health Professionals may refer to Part II of the paper entitled "Meridional (Astigmatic) Accommodation for further discussion on latent astigmatism.)

A quick screening test for manifest astigmatism (i.e. not latent astigmatism) can be found in the OAA description of astigmatism. One may also test oneself for the presence of more significant amounts of astigmatism by observing the "cross hair" patterns below.

The optical defect of astigmatism does not allow the line images of a cross to be simultaneously and clearly focused on the retina. If astigmatism is present, only the lines in one direction can be seen clearly at any one time.

Cover one eye without applying pressure to it. Look in the centre of either "cross hair" pattern . If there is no astigmatism present, the "cross hairs" should be simultaneously clear in both directions. This should apply when looking at either pattern.

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