What is a squint?

The expressions squint, cross-eyes, or cock-eyes or the medical term—strabismus—all refer to the same disorder—the two eyes do not look in the same direction. Normally the two eyes work in unison and the visual axes remain parallel, at all times, for all directions of gaze, except for convergence, a movement by which the eyes turn in during reading or near work.

What are the different types of squint?

Squint comes in various forms. One eye may look up while the other down, or they may be looking at each other or spread apart like a fish. They may even increase the angle between them when looking up or down or may seem squinted in one plane but parallel in another.

To simplify the discussion, all squints fall into 2 broad categories:

(1) Concomitant: (Latin: going together) Here the eyes maintain a fixed angle of displacement to each other in all directions of gaze. It is by far the most common type of squint.

(2) Paralytic: A squint which has resulted from paralysis of one or a group of eye muscles. Since the deviation of the two eyes will be maximal in the direction of the affected muscle, the squint will increase in one meridian and be almost absent in another direction.

To give an example, suppose the outer muscle (towards the temple) of the right eye is affected. If the eyes are turned to the right, the left eye will swing in but the right eye, since its outer muscle is affected cannot pull the eye out and thus remains paralysed in a halfway direction. However if the eyes are turned left, there will be no squint and to an observer the eyes will look parallel or normal.

When is a squint not a squint but still a problem? What is phoria or latent squint?

Normally the two eyes are maintained in a parallel position by the controlling effect of fusion. When the two eyes look at an object, the brain tries to "fuse" the two separate images into a single image, and to do that, sends orders to the two eyes to remain in a fixed position to each other.

If this fusion is removed for any reason, even by simply covering one eye, or due to weakness in vision in one eye, the eyes no longer seem straight when looked at. However, if the patient knows he is being observed or is told to make his eyes straight, he can voluntarily do so himself. Thus he has a squint, but can "voluntarily" correct it himself.

This is termed phoria. It is also termed "latent" squint for as long as fusion is holding them straight the eyes will no longer squint.

The importance of phoria or latent squint is that, it is a potent cause for headaches and eye aches. Recognised early, not only can frank or "apparent" squint be prevented, but it is eminently treatable in most cases by simple exercises and/or by corrective glasses.

What are the symptoms of latent squint or heterophoria?

The symptoms arise because of the continuous effort which has to be put in to keep the eyes straight. As an analogy, if one front tyre of a car is almost flat, the steering wheel keeps pulling in that direction, the arm gets tired and the shoulder pains in the effort to keep the car in a straight direction.

The commonest symptoms are:

(1) Headaches or aching of the eyes

(2) Intermittent blurring of print while reading

(3) Tendency to occasionally see double as the "fusion" holding mechanism tires out due to overstrain.

How is latent squint detected?

The technique is simple—dissociate the two eyes, by presenting them separate images so that they cannot fuse. Since there is no fusion all the deviation will show itself.

The simplest is when the doctor covers an eye, and lets you look at a light while rapidly covering and uncovering the eye under observation.

Alternative methods use a Maddox rod—a corrugated red glass which converts a spot of light to a line. Thus by looking through the rod, one eye sees a red line while through the other open eye the spot of light is seen. By matching the red line to the spot, the degree of squint becomes obvious, and can be measured. The same test for near objects is done by using a Maddox wing which uses an arrow seen by one eye and a graduated scale with the other eye.

Finally, the most sophisticated of all testing devices, the synoptophore, gives an unequivocal answer.

What is the treatment for latent squint?

The most common cause for a latent squint is a spectacle number in only one eye (a refractive error). Thus, prescribing appropriate spectacle glasses can cure the squint.

If the cause is inadequate ability to converge for near or to maintain fusion under stress, exercises on a synoptophore are curative.

In selected cases, giving special prism-controlled glasses is helpful.

Surgery is kept as a very last resort, if all exercises and alternative control methods fail.

What is concomitant squint?

A squint in which the eyes remain at a fixed angle to each other is termed concomitant squint.

Before a concomitant squint develops there is usually a latent squint, and this explains why it is so important to detect a latent squint in time. It is a very common type of squint.

What are the causes of a concomitant squint?

The most common reason is an error of refraction in one or both eyes which has remained undetected.

A common cause is an imbalance between the convergence (turning eyes inwards for reading or close work) and accommodation (changing focus from far to near to maintain clarity of the object viewed) mechanisms.

Absence of function, or an organic problem in an eye is also a common problem.

This type of squint can also occur rarely due to an inappropriate position of the eyeball in its socket or by changes in the bony socket causing a shift in the position of the eyeball.

What are the signs and symptoms of a concomitant squint?

The most obvious sign of a squint is the easily visible deviation. It tends to be more obvious if the person is tired or is looking into the distance. Since no effort is made by the brain or eye to maintain a parallel axis, there is no strain felt at all and no headache or eye pain.

If a squint has been there 'for a long time, the brain has learnt to "suppress" one image, so that though both eyes work, only one image is "seen" by the brain.

At what age does a concomitant squint develop?

A convergent squint (when the eyes turn in) occurs at an early age, 2-5 years. Typically a child with a high degree of hypermetropia will also have convergent squint. Again, in children, a latent squint, if it breaks down, usually becomes a convergent squint. A squint which is latent may become obvious after a bad fright, measles or any other weakening illness.

A divergent squint (when the eyes turn out) is more common in myopes and often occurs at a later age. It tends to remain intermittent for a long time before becoming an obvious apparent squint. This type of squint is also typical of loss of vision in one eye occurring in later adulthood.

Typically, a divergent squint is also seen in patients who have had a cataract operation in one eye, the other eye being normal. Since only the normal eye is used, after a few years, the operated eye starts diverging outwards. This type of deviation could have been prevented if a contact lens had been used after a cataract operation.

What is the treatment for a concomitant squint?

A squint is said to be completely cured if the visual axes are parallel and binocular vision is achieved. Though the squint is physically corrected, in a fair percentage of cases, without the use of exercises, binocular vision will not be achieved and thus the correction is a "cosmetic" correction rather than an "optical" correction.

Hence treatment should be along the following lines:

(1) Correction of any refractive error with spectacles or contact lenses: If a squint is purely because of a refractive error, the squint may either decrease markedly or simply go away by the appropriate use of lenses.

(2) Occlusion (or closure of one eye): If a squinting eye is optically weak and the image is being suppressed, it must be given an opportunity to build up its power. The easiest way is to close the normal eye, thus making the weak eye do the work. The normal eye is thus "closed" or "occluded" by a rubber occluder or by a patch. Since it has a bad cosmetic appearance the usual way is to use a small deep-coloured contact lens which no one can see. Sometimes use of certain drops can sufficiently blur the vision and these are called medical occluders.

In certain cases, however, occlusion can do more harm than good, and should only be done under competent medical supervision.

(3) Orthoptic training: (Greek: ortho: straight; optos: vision). Basically, a training using special exercises on instruments designed to straighten a squint. Orthoptic training works best at the age of 6-8 years. After the age of 14 it is not very successful.

Orthoptic training is useful before any surgery if the squint angle is very small and also after surgery to "fine tune" the muscles back to the exact normal position.

(4) Surgery

When should surgery be done?

An operation should be done if

(a) The angle of squint is 10 degrees or more

(b) The angle of squint is increasing

(c) Orthoptic training has failed to correct a deviation in a child in a reasonable span of time

(d) The child is past the age of 9 years (after 10 there may be permanence of amblyopia (weak or "blunt" vision) which will not go back to normal later on.

How is the operation for squint carried out?

Since the eye muscles are attached outside the globe, the eyeball itself is never entered and all surgery is done from outside.

Basically, the muscles are detached from their insertion and reattached to another spot thus rotating the eyeball straight.

Though the technique sounds simple it is sophisticated and in the hands of a good surgeon, excellent results are achieved.

How long does a squint operation take?

The time depends upon the number of muscles that need to be operated. Usually it takes from 20 minutes to an hour. Though the operation is time-consuming as compared to other eye operations, it is comparatively safe.

What type of anaesthesia is used for squint surgery?

In adults, though a local block (with injections only around the eye—the patient is fully conscious) can be given, general anaesthesia (gas anaesthesia) is the preferred mode. In children, naturally, only general anaesthesia is used.

How long does the eye remain red after surgery?

Around 3 weeks. Glare glasses may be worn in public. However, redness is an individual factor, varying from patient to patient, and may take a little longer to go away. In about two months there is usually no trace of any surgery done to the eye at all.

Are there any precautions to be taken after surgery?

For practical purposes, none. Of course the patient should not strain, pick up heavy objects or be exposed to the sun or heat unduly. But all normal activities are permitted, and he can watch TV and cinema. Working at the table is permitted, after 3 days. The head can be washed after a week though the patient can have a bath daily below the neck.

What are the causes of a paralytic squint?

Essentially, the cause of a paralytic squint is a paralysed muscle. Hence the cause can be any disease process, affecting the nerve roots, the nerves themselves or the muscle.

What are the signs and symptoms of a paralytic squint?

The commonest symptom is double vision (diplopia). Since the angle of squint varies continuously, the brain is unable to suppress any one of the two images. Double vision is thus the most important complaint.

Tilting the head to the opposite direction of the paralysed muscles relieves the double vision, and hence the tendency is to turn the head in a position to "compensate" for the double vision. This compensatory head posture is thus characteristic of a paralytic squint.

Of course, the obvious sign of a paralytic squint is the constantly varying angle of squint increasing to a maximum at the paralysed side.

What is the treatment of a paralytic squint?

No surgical treatment is done for 6 months to permit the affected eye muscles to recover, which they do in a fair percentage of cases. Simultaneously, an effort is made to locate the reason for the paralysis.

Later treatment is designed to control or at least decrease the double vision.

Paralytic squint requires refined treatment which varies according to each individual case and will not be discussed further.

Dustin Flores

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