While the history is being taken from the parents, one should be making an assessment of the child. If the child is obviously shy or
nervous, a useful technique is to introduce something of interest to the child in the conversation with the parents. At this point, it is important not to approach the child directly but to allow him or her to make an assessment of the doctor. It is quite impossible to examine an infant's eyes in a noisy room, thus the number of people present should be minimal and they should not be moving about. The room lighting should be dim enough to enable the light of a torch to be seen easily. The first important part of the examination is to shine a torch at the patient so that the reflection of the light can be seen on each cornea. The position of these corneal reflections is then noted carefully. The more mobile the child, the less time there is to observe this. If there is a squint, the reflections will be positioned asymmetrically in the pupil. If the patient has a left convergent squint, the reflection from the left cornea is displaced outward towards the pupil margin. A rough assessment of the angle of the squint can be made at this stage by noting the abnormal position of the reflection. One of the difficulties experienced at this point is because of the continuous movement of the child's eyes, which makes it difficult at first to know whether the light is being accurately fixated. By gently moving the torch slightly from side to side, it is usually possible to confirm that the child is looking, albeit momentarily, at the light.
Once the light reflections have been examined, the cover test can be performed. Once again the reflection of light from each eye is noted, but this time one of the eyes is smartly covered, either with the back of the hand or a card. If the fixating eye is covered, a movement of the nonfixing eye to take up fixation can then be observed (Figure 14.3). After some practice, it is possible to detect even slight movements of this kind. The result of the test can be misleading if the nonfixing eye is too weak to take up fixation, and quite often, an assessment of the vision of the nonfixing eye can be made at this stage.
If, having performed this first stage of the cover test, no deviation can be detected, the cover can be quickly swapped from one eye to the other and any movement of the covered eye can be noted. That is to say, the latent deviation produced by covering one eye is spotted by noting the small recovery movement made by the previously covered eye. Finally, the cover test must be repeated with the patient looking at a distant object. One type of squint in particular can be missed unless this is done. This is the divergent squint seen in young children, which is often only present when viewing distant objects. The parents might have noticed an obvious squint and yet testing by the doctor in the confines of a small room reveals nothing abnormal,with ensuing consternation all round.
After the cover test has been performed, it is necessary to test the ocular movements to determine whether there is any muscle weakness. At this stage, it is usual to instil a mydri-atic and cycloplegic drop (e.g., cyclopentolate 1% or 0.5%) in order to obtain a measure of the refractive error, by retinoscopy, when the eyes are completely at rest. Next, the optic fundi are examined.
In most instances, the nature of the squint becomes apparent by this stage and further testing of the binocular function and more accurate measurement of the angle of the squint are carried out using the synoptophore.
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