General EYE ADVICE

Meridional Accomodation and Correction of ATR astigmatism in Children and Adults

ATR astigmatism is a relatively common source of patient-practitioner conflict. Correction of this type of astigmatism upon normal methods of refraction may cause the patient to complain of eyestrain symptoms. In the small proportion of younger patients whose eyes produce an excessive amount ATR astigmatism upon near viewing, often the best solution is to prescribe "performance" lenses (i.e. low plus-powered lenses), in order to reduce both the amount of near focusing and also of the ATR astigmatism. This will prevent the problem from occurring and is an example of proactive prescribing. On the other hand, prescribing reactively by correcting for the amount of ATR astigmatism that gives the clearest vision (i.e. the result that is found upon normal testing), can lead to patient complaints of asthenopia etc.

Similar problems are more commonly encountered in people of middle age or older who engage in close work without, or with a sub-optimal presbyopic correction. (Refer to Section D for discussion on correction of presbyopia and also for recommendations.) In older age, the lens of the eye cannot change its focus adequately despite the individual's effort in attempting to focus. If the appropriate correction for presbyopia is not worn, the effort exerted in attempting to focus will unavoidably stimulate reflex MA in the normal way. The amount of reflex MA that is stimulated is mainly genetically determined and can vary between individuals. As the lens in the eye is not changing its shape, there is no benefit in the reflex MA. In fact, reflex MA will create ATR astigmatic changes of the cornea over longer periods of time, thus reducing the clarity of vision.

In this case, if the practitioner prescribes the corrective lens that accounts for the ATR astigmatism and gives the clearest vision at the time of the examination, the patient may complain of eyestrain symptoms when wearing the new spectacles. If the patient is still encouraged to wear them for longer periods of time, the eyes may adapt to the prescribed astigmatic lenses by undergoing permanent ATR astigmatic changes of the cornea. This adaptation occurs to a variable extent between individuals. The eyestrain symptoms will subside only in response to permanent corneal changes, otherwise they may persist indefinitely. This adaptation usually takes a few weeks to a few months, depending on various factors such as the length of time the spectacles are worn etc. The eyestrain symptoms as well as the permanent astigmatic changes can be avoided by wearing the optimal correction for presbyopia when reading. This prevents the ATR astigmatic changes of the eye and the associated problems in correcting them.

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