ever, he was more liberal than most succeeding writers, and even the latest text-books on ophthalmology make no reference to the condition. The first notices of cases of treatment of "insufficiency of the externi," in which no strabismus existed, and in which important results were obtained, were reported by myself in various papers from 1876 forward. In the memoir to which this discussion is supplemental, more especial consideration was devoted to this condition than had been given to it in all previous writings, and the many instances of remarkable relief obtained from the correction of this anomaly related therein precede any considerable discussion of the subject, and, indeed, constitute the principal contribution to it up to the present time.

"Insufficiency of the interni" is the condition to which muscular asthenopia has been generally attributed. We have already seen that hyperphoria is an element of the first importance in muscular asthenopia, and a careful perusal of the foregoing memoir will convince the reader that esophoria is also of equal signifi cance with, if not of greater importance than, "insufficiency of the interni." It is certainly of more frequent occurrence, and is, in a greater proportion of cases, attended with distant reflex disturbances.

Among the symptoms very commonly observed as resulting from esophoria, are pain in the back of the head and in the back of the neck. Such pains often succeed an hour's visit to a gallery of pictures, attendance at a public gathering, where one confines the gaze for a considerable time upon a speaker; and travel in a

rail-car, when the individual, the subject of esophoria, looks out upon the rapidly-changing objects of the landscape, is often the precursor of such occipital headaches.

Nervous exhaustion, palpitation of the heart, pain between the shoulder-blades and at the lower part of the back, dyspepsia, and habitual constipation are among the very common reflex nervous phenomena resulting from esophoria.

To ascertain the existence of esophoria and its degree, the test for hyperphoria having been already made, we first place a prism of about 7° with its base down before one of the eyes and cause the person examined to look at an object twenty feet distant. Double vision results with the image before which the glass is placed above its fellow. If, now, the higher image deviates in the direction of the eye before which the glass is placed, if the deviation is homonymous, there is esophoria, measured by the degree of prism, placed with its base out before either eye, which brings and holds the two images exactly in the same vertical line. In making this examination hyperopia or hyperopic astigmatism, if of higher grade than 50 D, should be corrected by appropriate glasses. Moderate degrees of myopia or myopic astigmatism have little influence upon the test. After determining the degree of esophoria by the vertical prism, the amount of abducting power is to be ascertained. Prisms with the base in are employed, requiring the person examined to make the strongest effort to blend the double images. The strongest prism which can be overcome marks the

power of abduction. This power should be equal to overcoming a prism of 8° with the base in.

Let us suppose that esophoria of a certain degree has been found, and that there is approximately a corresponding restriction of the abducting force. The diagnosis of esophoria of the given amount is clear. But if, by the vertical prism, no deviation is shown, and there is still a restricted abduction, there is probably latent esophoria equal, at least, to the difference between a prism of 8° and that with which images can be blended.

But let it be supposed that a very considerable degree of esophoria is found with a power of abduction exceeding the standard given above. One of two conditions must be presumed: There may exist an actual deviating tendency inward, and by constant efforts at its correction the power of the external recti may have been so greatly developed as to enable the individual to accomplish more than the usual abduction; or, more probably, there exists hyperphoria. In this later case the esophoria may be apparent, the result of a swinging movement given to the eyes in the test, and the actual balance may be neither inward nor outward. The utmost caution and great patience are required in the management of this class of cases. A condition exactly opposite the one just supposed will be considered in the discussion of exophoria. Again, should esophoria be found when testing for the distant point, and exophoria be shown in accommodation, we are to suspect hyperphoria, and the case should be carefully observed until this question is satisfactorily deter

mined. After having made the examination at the distance of twenty feet, examination with the vertical prism is made at a distance of about eighteen inches. If esophoria is found, it is esophoria in accommodation.

TREATMENT OF ESOPHORIA.

Esophoria may, under certain circumstances, be treated by prismatic glasses; if refractive errors exist, the prismatic element may be combined with the spherical, or cylindrical glasses.

This is the method of a crutch, and is inconvenient and by no means uniformly successful. Indeed, successful relief to esophoria, by means of prisms, would appear to be rather exceptional. It is a proper method of treatment only when better methods can not be adopted. There are several reasons in the nature of such a correction why it should be unsatisfactory, which need not be discussed here.

The radical and best method is tenotomy of one or both of the interni, performed by the method already described at page 203. Before resorting to an operation it is always advisable that the power of adduction should be fully developed in the manner that will be shown in the section on exophoria. An adducting power of 50° should be shown prior to the operation.

EXOPHORIA.

This is the condition which has been described in text-books as "insufficiency of the interni." The condition, however, differs in the respect that, whereas "insufficiency of the interni" has, by Graefe and in

the text-books generally, been determined by the dotand-line test at a near point, exophoria is the condition found at a distance when no accommodation is employed. The condition described in text-books is here known as exophoria in accommodation. The conditions found by the tests known as the "cover-tests," and by holding an object near the eyes to observe the deviation of one or other, are perhaps better included in the limits of the subject of strabismus.

Exophoria is discovered by means similar to those described for esophoria. If, with the vertical prism, the images cross, if the image seen by the right eye is at the left, and that seen by the left is at the right of the other, exophoria exists in the degree measured by the prism with its base inward, required to bring the two images to a vertical line.

Exophoria in accommodation is tested in the same manner, but at the near point. If, with a certain degree of exophoria, abduction exceeds 8°, we have an undoubted condition of deviating tendency outward. If, on the other hand, exophoria is attended with restriction of abductive force, we are to presume that hyperphoria exists, and that, as in the case of esophoria, under the reverse conditions, the apparent exophoria is the result of the swing resulting from the hyperphoria.

Exophoria in accommodation is often associated with esophoria, and should never under such circumstances be mistaken for an actual tendency of the eyes to deviate outward.

The symptoms of exophoria are, perhaps, more fre