is manifest is to be considered in its relation to the power of abduction.

Deficiency of abduction resulting from hyperphoria will be noticed below.

The power of overcoming prisms with the base up or down may be tried before or after the trial for abduction. Commencing with a very weak prism, we try stronger, until the strongest that can be overcome in one direction is found; then the strongest in the opposite direction. A prism with its base down before one eye is equivalent in its action to a prism with its base up before the other. The amount of power shown in overcoming a prism with its base down before the right eye is the degree of right sursumduction. If the prism is placed before the left eye in the same direction, or if it is turned with its base up before the right eye, it indicates the degree of left sursumduction. We can not make accurate determinations of both right and left sursumduction, if the test for one follows without interval after the other. It is, therefore, well to test in one direction before the test for abduction and in the other after it.

The average ability of overcoming prisms in this manner is about 3°. In high grades of myopia it may reach 8° or 10° in each direction.

Finally, the amount of adduction is to be determined. Prisms are to be placed before the eyes with the base out and the strength gradually increased until the images can no longer be blended. The highest grade of prisms overcome marks the adducting power.

The standard of adduction should be about 50°, but many, who after trials repeated daily for two or three times will accomplish an adduction to this extent, will not accomplish half the amount at the first trial.

All the tests for sursumduction, abduction, and adduction should be made at the distance of twenty feet.

HYPERPHORIA.

Hyperphoria is that condition in which, with the ability to maintain binocular vision, there is a tending of one visual line in a direction above that of the other.

Strabismus, in which there is an actual turning of the axis of one eye above the other differs from hyperphoria in the absence of ability to maintain single vision. Strabismus sursumvergens, and deorsumvergens were described and operative measures for their correction were long since pointed out. Special attention was first called to the condition of hyperphoria as an important and frequent anomaly of the ocular muscles by the author of this work.

Among the anomalous tendencies resulting from faults of equilibrium of the eye-muscles, hyperphoria is of pre-eminent importance.

A slight deviating tendency in this direction is often of greater account than one of a considerable degree in others.

The ability of the eyes to adjust the visual lines for the correction of a difference in their direction in the vertical meridian is much less than that for correcting a similar difference in the horizontal line. It has been

already shown that the power to overcome a prism placed with its base up or down before an eye is usually limited to about 3°, while in abduction a prism of 8° and in adduction prisms of 50° may be overcome when the normal standard of power in these directions exists. It is evident, therefore, that a deviating tendency of 1° or 2° in the direction of hyperphoria creates an excessive demand for correction upon muscles illy calculated to perform the duty.

A still more important element in the results of hyperphoria is its influence upon the action of the lateral muscles.

In hyperphoria the eyes may be so influenced in their movements that, when directed to a distant object at the same height as the eyes, there is a strong tendency of the visual lines inward (esophoria); but if directed to a near object, especially if it is below the plane of the eyes, the visual lines swing outward, causing a very marked exophoria in accommodation, or, as it is familiarly known, insufficiency of the interni. Many of the most intractable cases of insufficiency of the interni are the result of this swinging movement of the eyes, and it is not rare to see asthenopic persons who are armed with powerful prisms for the correction of insufficiency of the interni, who have no other muscular error than a slight hyperphoria.

Persons subject to hyperphoria are much more liable to be troubled with double images than those subject to simple exophoria or esophoria.

Vertigo and confusion of vision are extremely common symptoms of hyperphoria. Persons affected by

this anomaly, if weak or in ill health, often experience a dread of walking in crowded streets unattended, fearing that they may fall or suffer from mental confusion in the crowd.

The attitudes and facial expressions of hyperphoria, while not universal, are quite characteristic. The head is, in a very considerable proportion of cases, carried habitually toward one shoulder. If the right eye tends higher than the left, the head is carried to the left shoulder; if the left eye tends above, the head is at the right.

The efforts made by the eyelids to aid in forcing the eyes in position give certain peculiarities to the facial expression. One eye may appear partly closed, or both eyes are opened very widely with a kind of stare which has been described as "the hyperphoric stare."

The eyes in hyperphoria have, in many instances, an unsteady gaze. One eye may appear to float away from the other and then back again.

Vision is, in a considerable proportion of cases, affected. It has been found that, in more than fifty per cent of cases, vision is less than two thirds the normal standard.

Many cases of abnornal secretion of tears have their origin in this condition. They do not yield to the ordinary methods of treatment for such complaint, and are liable, by means of the excessive flow of tears, to result in distention of the lachrymal sac and in inflammation of the lining membrane of the nasal canal, leading to its contraction.

In its reflex results hyperphoria is an extremely im

portant element in neuroses. Especially in epilepsy and vertigo should it be looked for with great care.

TREATMENT OF HYPERPHORIA.

The best treatment for hyperphoria is tenotomy of the muscle which forces the eye out of its proper direction. It is not always easy or even possible to determine to which muscle we are to attribute the vicious tendency. The superior rectus of one eye may be short, causing too great tension upward, or the inferior rectus of the opposite eye may be at fault, tending to draw the eye downward, or one of the four oblique muscles may cause the loss of equilibrium. With all these elements of uncertainty, the highest skill of the surgeon may be demanded in forming a correct conclusion. A complete knowledge of what is known of the physiological action of the various eye-muscles is essential in this examination. In the majority of cases, however, in which the hyperphoria does not exceed three degrees, it is proper to relax either the superior rectus of the eye of which the deviating tendency is upward or the inferior rectus of the other. general, it will be found best to select the superior rectus. If more than three or four degrees of deviating tendency is found, it is better to correct a part upon the superior rectus of one eye and what remains of the defect upon the inferior rectus of the other eye some days later.

In

The method of performing tenotomy in these cases of deviating tendencies less than strabismus has been *See page 135.