DIVERGENCE INSUFFICIENCY: A CLINICAL STUDY* AVERY DE H. PRANGEN, M.D. Rochester, Minnesota AND (By invitation) FERDINAND L. P. KOCH, M.D. Rochester, Minnesota Anomalies of the convergence-accommodative mechanism have long been recognized as a source of ocular discomfort. The importance of pathologic divergence, particularly di- vergence insufficiency, has not been fully stressed. In our experience, divergence insufficiency is a definite clinical entity which causes much asthenopia. It also appears to be amenable to treatment. Divergence insufficiency is distinguished from other types of esophoria by the fact that in the former condition the esophoria is greater in distant vision than it is in near vision, and the power of divergence or abduction is definitely below the normal. These cases may be divided further into those in which there is insufficiency, paresis, or paralysis, the differentiation here being largely a matter of the degree of severity, clinically, of the divergence difficulty. A similar classification is used clinically to describe various degrees of accommodative weakness. Embarrassment of divergence varies from a low-grade insufficiency to an actual paralysis of the function. Dunphy and Dunnington' reported cases of divergence paralysis and also mentioned cases reported by Parinaud, Theobald, Duane, Holden, Cutler, Wheeler, Alger, and Zent- mayer. * From the Section on Ophthalmology, The Mayo Clinic, Rochester, Minnesota. 136 PRANGEN AND KOCH: Divergence Insufficiency 137 The typical findings in divergence paralysis are the pres- ence of a homonymous diplopia in distant vision but not in near vision; the ocular excursions are normal, and there is a loss of diverging power. Convergence is unaffected. If these cases are to be accepted as cases of divergence paralysis, one must assume the existence of a center for divergence similar to the accepted center for convergence in Perlia's nucleus. Bielschowsky was of the opinion that a divergence innerva- tion is required not only to divert the visual lines from con- vergence into parallelism, but also to overcome an esophoria. This writer observes that vergence tests tend to prove this. Duane also believed that such a center existed in the vicinity of the nucleus of the sixth cranial nerve. Bergmann, Pugh, and Duke-Elder believed that divergence is accomplished by relaxation of convergence through reciprocal innervation. Maddox assumed that divergence paralysis occurs. Riley held that a center for divergence can be suspected on clinical grounds, although its anatomic site is as yet unknown. As suggested by Bielschowsky, it would seem difficult to con- ceive why only convergence should lack an antagonistic in- nervation. It seems that there must be a definite center for divergence in order to carry out the refined control which is exhibited clinically over the all-important convergence- divergence relationship. This is so carefully balanced a function that its operation by a one-sided control-that is, by convergence only-is difficult to visualize. Cases of divergence insufficiency were reported by Dun- nington,7 Davis, Peter, Maddox, Pugh, and Bielschowsky. These authors pointed out the discomfort caused by the con- dition, the association of physical and psychic disturbances, the exaggeration of the condition by presbyopia, the lack of response to orthoptic treatment, and the possibilities for relief by the use of prisms base out. On the last point, opinion was divided. Operation was advised in cases in which the condition did not respond to other forms of treatment. In diagnosing divergence insufficiency, it is first noticed 138 PRANGEN AND KOCH: Divergence Insufficiency that the eyes show an esophoria both in distant and in near vision. It is further observed that the esophoria is definitely greater in distant vision than it is in near vision. When readings of vergence are taken, it is seen that divergence is well below normal, whereas convergence is above normal. If one determines the rest position, or phoria, slowly, thus fatiguing binocular fixation, when the cells of the phorometer or trial frame are cleared, and, preparatory to taking readings of vergence, the eyes fix the light at six meters, they will often exhibit a homonymous diplopia, which at once will show their deficient diverging power. This diplopia may disappear quickly on resumption of binocular fixation, but it will usually reappear as one proceeds to fatigue divergence by repeated tests of ability to overcome prism base in. Such eyes may overcome four to five degrees of prism base in at first, but as the test is prolonged this amount quickly drops to 0 or one or two degrees of prism base in. As the diplopia is elicited in this manner by fatigue, it will often be found that a prism base out, of from two to six degrees, is required in order to maintain single vision at six meters. Incidentally, this is a good way to determine how much prism base out is needed for distant use. Convergence being unopposed is usually high-between 20 and 30 degrees. When readings of vergence are taken in near fixation, the same re- lations are found, but we have come to regard divergence as a significant finding for distant fixation only, and to regard convergence as a significant finding for near fixation only. In other words, divergence is typically a function of distant vision and should be so measured, and convergence should be measured for near vision. In our experience the phenomenon of homonymous diplo- pia on fatigue of fixation has not been found frequently in near vision. In the cases of divergence paralysis, homony- mous diplopia for distance is, of course, a constant finding. In a typical case of divergence insufficiency (Case 52 in our series), when the ametropia was corrected there was an eso- PRANGEN AND KOCH: Divergence Insufficiency 139 phoria of ten degrees at six meters and of five degrees at 0.33 meter. Divergence at six meters was one to two degrees, whereas convergence at 0.33 meter was 25 degrees. There was also a left hyperphoria of three and one-half degrees for both distant and near vision. When fixation was fatigued at six meters, homonymous diplopia was elicited and five de- grees of prism base out were required to maintain single vi- sion. Inasmuch as this corresponded to the amount of esophoria found in near vision, five degrees of prism base out were prescribed to be worn constantly, together with three and one-half degrees of vertical prism. The eyes were hy- peropic, and the patient was thirty-one years of age. He had had much difficulty with near work and had left college. With this correction he was greatly pleased, he returned to college, and graduated. In the present study we are reporting 54 cases of esophoria in which an analysis of the findings seemed to indicate a divergence insufficiency. Thirty-seven of these were cases of frank divergence insufficiency, 10 ekhibited functional eso- phoria, four were cases of paralysis of divergence, and two were cases of paresis of divergence; one case of excessive convergence was included because relief was obtained by the use of prisms base out. In all but seven cases in this series the patients were between twenty and forty-five years of age-a period of life when the greatest demand is made on the eyes for intensive close work. Among younger people there is less demand on the eyes and greater reserve power, whereas elderly persons are aided by presbyopic additions. As to sex, the patients were about, equally divided: 25 were males and 29 were females. Occupation seemed to play a definite role, as 34 patients were engaged in performing near work. Normal vision was found in all cases; no amblyopic eyes were observed. Accommodative power was low in 11 cases, and in five it was definitely subnormal. In 14 cases the patients were wearing glasses that afforded very incom- plete correction of the ametropia, this adding to the strain 140 PRANGEN AND KOCH: Divergence Insufficiency of an already defective ocular apparatus. Hyperphoria was seen in 34 cases; it was often of a changing and fluctuating type. It was found for distance only in eight cases. The hyperphoria averaged one degree, and the most marked was eight degrees. In one case the hyperphoria was 11 degrees for distant vision and seven degrees for near vision; this appeared to be the primary difficulty, the divergence weak- ness being of secondary importance. Divergence averaged from two to four degrees; it was 0 in 11 cases, although the condition seemed to be frankly paralytic in only four cases. In the paralytic group the patients complained of a persistent homonymous diplopia at a distance and in all fields of vision, but not in near vision. There was, as a rule, more than 20 degrees of convergence. Hyperopia occurred in all but 10 patients, myopia was present in eight cases, mixed astig- matism was present in three, and antimetropia occurred in one case. Anisometropia, which was found in 26 cases, was a somewhat constant source of annoyance to these eyes. The esophoria recorded was from 3 to 18 degrees at six meters, and from 2 to 10 degrees at 0.33 meter. In 20 cases functional derangements, such as chronic nervous exhaustion, functional disorders of the stomach, of the genito-urinary tract, biologic inferiority, asthenia, and menopausal disturbances, were present. Exophthalmic goiter was noted in one case, and migraine was present in two cases. In the cases in which paralysis occurred, vascular disease was found in one case, ovarian dysfunction in one, mental depression in one, and exophthalmic goiter in one case. From a neurologic point of view, 12 instances of psychopathic personalities were noted; 26 patients were neu- rasthenic in type, and 10 patients were obviously tense and high strung in their make-up.