Eye Care Blog

Strabismic disorders in the adult may also be associated with certain diseases and drugs affecting the nervous system. In the child, however, the chief causes are congenital. Treatment of squint can be generalized as follows. The first step must always be to establish why the eyes are not working together, and this necessitates a full ophthalmic examination. Special (orthoptic) tests to measure the degree of weakness in the affected eye and to clarify whether the defect is sensory or motor, using electronic equipment, may be required, especially if the patient is a child. Very often the treatment itself will then consist of correcting any refractive error present in the eye, either with spectacles or, if the two eyes are of a very marked difference in power, with contact lenses. But it is also important to develop and strengthen the vision in the weak eye if the patient is very young (and the vast majority of squints do occur among children). This can be most effectively achieved by covering up the good eye for a period up to several months, a frustrating experience as the child’s natural inclination is to depend on the good eye and not worry so much about the other one. Orthoptic examination at regular intervals determines how effective this procedure is. If the two eyes cannot learn to co-ordinate with each other, then this sensory part of the treatment will be abandoned. This often leads patients to take themselves, or to be taken, to other practitioners, though nearly always with the same end result.

At some stage or another the ophthalmologist has to decide whether nature and non-invasive remedial treatments will effect the best cure, or whether he should operate. If it comes to the latter he must then further decide which muscles to operate on. This is a difficult matter of judgement, but if the correct decision is taken good surgery can result in an acceptable cosmetic appearance and, in rare instances, even prevent the development of an abnormal head posture.

Since there are six muscles in each orbit, making twelve in all, some explanation of what the surgeon must attempt is necessary. In almost every case the surgeon will know which are the strong, and which are the weak muscles; but there are many cases where cause and effect cannot be determined until the operation has commenced. Either a weak muscle can be strengthened or a strong muscle weakened, and so both eyes will often be operated on at once in order to achieve a new muscular distribution. All this requires the most delicate calculations, particularly as it is unusual for more than two muscles in each eye to be used at any one time, and sometimes more than one operation is required.

The operations themselves are always on the outside of the eye-globe, and do not affect the inside of the eye. They are therefore at best attempts to restore sight to a bad eye or binocular vision to both eyes. At other times they are performed to make the patient look more normal and nothing more.

False Squint

False squint, or pseudo-strabismus, is associated only with infants. A baby’s face is in certain obvious respects different to an adult’s. For example, the bony features are not well marked, and the cheeks are proportionately fat. The eyes too are large relative to the other features, while the bridge of the nose is sunken and undeveloped. At this early stage there may be folds of skin from the upper eye-lid to the side of the nose actually covering the corner of the eye. When this occurs it is called epicanthus. If the baby looks to one side, the eye on the far side will partially disappear under the skin fold and an apparent squint results. In fact nothing at all is wrong, but it is sometimes difficult to convince the baby’s relatives that the skin-fold will eventually disappear as the bridge of the nose develops and rises.

Nystagmus

In the same class of ocular disorder as strabismus may be placed the troublesome condition known as nystagmus, or shaking of the eyes. Typically, nystagmic eyes move quite involuntarily from left to right and back again; less commonly they shake vertically. When the movement is even and rhythmical the condition is called pendular nystagmus; but when the movement is more frenzied, it is called jerk nystagmus. The syndrome itself is either present from birth, when it is often associated with albinism, or comes about in conjunction with some other sensory disorder. It may also occur as an exaggeration of normal physiological nystagmus, when the patient is severely ill or under the influence of drugs, particularly barbiturates. There are also some rare forms of nystagmus linked to diseases of the nervous system.

Congenital nystagmus, being the most common form of the complaint, needs a little further description. In most instances the eyes shake with a horizontal movement, often alternating between fast and slow phases. The shake becomes worse when the eyes are focused in the distance; when looking at close objects it diminishes. Usually there is nothing grossly wrong with the optics of the eyes, and the individual does not experience any intolerable difficulty in, say, reading. Contact lenses, even of zero power, may improve the vision, while anxiety will tend to worsen the condition. The future may provide a medical cure, but at present there is no means of eradicating this affliction.

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