Chapter XVIISYMPTOMS OF HETEROPHORIA

Thesedepend on the kind of error present as well as the degree and widely vary.

In general, they may be said to fall into three classes—(1) defective vision, (2) pain of greater or less degree—(3) reflex symptoms.

Defective Vision.The first class may be present, even though each eye has a normal visual acuity; since, even when compensation is very good, the brain gets the impression of two objects, nearly, though not quite fused; and vision may be considerably worse with both eyes together than with either eye singly.

When compensation is considerably impaired, the diplopia becomes more and more persistent, till the brain finally makes choice of one image as more satisfactory, entirely suppressing the other. Visual acuity may not suffer in either eye; but vision being no longer binocular, everything is seen in the flat, the judgments of depth and distance being regularly more or less defective. While this is a tremendous disadvantage in many occupations, people gradually and not infrequently become accustomed to these visual defects and are not conscious of the handicap.

Pain.It is quite different with the second set of symptoms, which are always accompanied with pain. In fact, the character of the subjective symptoms in refractive errors and muscular imbalance is so similar that it is practically impossible to differentiate in many cases.

In muscular asthenopia, however, in addition to becoming easily tired, the patient often complains that letters seem to jump or run together or he may contend that he sees double for an instant; or again that he can “feel his eyes turn” involuntarily in their sockets. These pains or conditions are sometimes present only during actualuseof the eyes. At other times they persist for hours. In some cases, after days or weeks of overstimulation, an explosion in migraine form occurs at irregular intervals. This condition often lasts a day or two.

Reflex Symptoms.In the third and last case, there are other reflex symptoms—such as dizziness, nausea, fainting, indigestion, insomnia and pains in other portions of the body—sometimes stimulating organic diseases.

The possibility of heterophoria as a factor in chorea, migraine, neurasthenia and other diseases which may be primarily due to unstablenerves, equilibrium is not to be forgotten. It is a notable fact that when the fusion compensation fails so completely that one image is entirely suppressed, or the diplopia is so great as to be overlooked, the symptoms often cease entirely.

The treatment of heterophoria depends on a careful study of each individual case, but it cannot be too strongly emphasized that in the great majority of cases the subjective symptoms disappear after a full correction of the refraction is made.

In many cases, if the visual acuity in each eye be made normal, the fusion impulse alone will be sufficient to restore compensation.

Many cases of esophoria result from overstimulation of the centers for convergence and accommodation, made necessary by hyperopia and astigmatism, entirely disappearing when glasses abolish the need of accommodation. Cases of exophoria are sometimes due to the abnormal relaxation of accommodation and convergence which secures the best distant vision in myopia. Likewise the correction of myopia, by increasing the far point, may diminish the amount of convergence necessary for near vision.

Prisms for constant use are often prescribed, so placed as to help the weak muscles and counteract the strong. For instance, in esophoria we find the prism which, base in, will produce orthophoria for distance and prescribe a quarter of it, base in, before each eye. While this is very successful in some cases, the tendency in others is for the externus to increase slightly from constant exercise in overcoming the prism, while the internus decreases in proportion to the amount of work of which it is relieved. Prisms for permanent use are very beneficial in vertical deviations, since when the images are brought on the same level they require much less effort to secure fusion; and when prescribed base up or down, the effect secured is commonly an unchanging one.

We sometimes take advantage of this tendency when we prescribe for constant use weak prisms with the apex over the weak muscle, which gradually becomes strong from the exercise of overcoming it. This plan is effective only in patients who have a strong fusion impulse, and the prism selected must be weak enough to be easily overcome. We can accomplish the same effect by decentering the patient’s refraction lenses.

For instance, a convex lens so placed that the visual line passes the reverse will be the case if the lens is concave. The amount of prismatic action depends on the strength of the lens and the amount of decentering, the rule being that every centimeter of displacement causes as many prism diopters as there are diopters in that meridian of the lens. Thus +1 sphere, or cylinder axis 90, decentered one centimeter outward, is equivalent to adding a one degree prism diopter lens, base out.

These are terms denoting a condition in which both eyes are capable of abnormal rotating toward the right or left, as the case may be. The movement in the opposite direction is most common. The patient can often rotate his eyes 60 degrees toward the right, and to perhaps only 40 degrees to the left. His position of rest is parallel with his visual lines, but to theright, in looking at objects directly in front, he is much more comfortable with his head turned slightly to the left.

It is difficult to account for, except on the theory that definite movement of the eyes is rather to the right than to the left in most occupations. The position of the paper in writing at a desk tends toward dextrophoria; in reading, we move our eyes steadily from left toright and then begin a new line by a single brief movement to the left; the things that a man uses most—whether he be laborer or student—are kept within reach of the right hand, and in referring to them the eyes are constantly turned toward the right.

However, when these conditions result from other imbalances, they must be treated more carefully. For instance, a patient whose right internus is paralysed or congenitally defective on looking to the left, has a cross diplopia which vanishes to the right; as a result, he soon assumes a habit of carrying his head in this position. Ordinarily, this will cause no discomfort; but if the left internus is so weak that it cannot follow the right externus to its position of greatest ease, the visual lines are evidently different and the case must be treated as an exophoria.

If, on the other hand, theleftinternus over-balances the right externus, the condition is an esophoria and must be treated as such.

Similar reasoning applies to the conditions known as Anaphoria and Kataphoria, in which the visual lines are parallel to each other but directed up or down with regard to the horizontal plane of the body.

In the first, owing to congenital abnormalities, the eyes usually tendupward and the individual must go about with his chin on his chest, so that his eyes may look in front and yet remain in the position of rest. In the second, the chin is held in the air and the body arched backward.

But, unless extreme, neither of these conditions causes more than cosmetic difficulty and both should be undisturbed owing to the extreme difficulty of securing the same operative effect on both eyes. Suitable prisms are much more likely to be beneficial.

Supports for HoldingThe Ski-optometer

Floor StandWall Bracket

Floor Stand

Wall Bracket

Chair ClampChair Attachmentwith Upright

Chair Clamp

Chair Attachmentwith Upright

Choice may be made from any of the above. The Wall Bracket is recommended, unless refractionist is provided with a specialist’s chair, to which the Chair Attachment with Upright may be attached.

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