BARRIERS AND AIDS TO FUSION 1151

flexes. The direct and simultaneous stimula­tion of the two maculas, and hand and eye coordination are fundamental aids.

3. The consummation of the reflex arc is in itself a direct intrinsic stimulation to further response, especially if it is in the nature of a biologically superior response.

4. The elaboration of two uniocular images in the cortex and the arousing of the factors of attention and interest so that, with increased permeability of the associa­tion pathways, fusion is elaborated in a final synthesis.

SUMMARY

We have considered the theories of fusion and the necessary neural and physiologic factors. Reference has been made to the barriers to fusion and their removal by refractive, orthoptic, and operative means. The validity of orthoptic training on the basis of our present knowledge of the learn­ing process is demonstrated and the attain­ment of fusion considered in the light of cortical neurophysiology.

402 Cobb Building (1).

REFERENCES

1. Chavasse, B. : Worth's Squint. London, Baillière, Tindall & Co., 1939. 2. Duke-Elder, W. S. : Textbook of Ophthalmology. London, Henry Kimpton, 1932, v. 1, pp. 1034-

1035. 3. Fulton, J. F. : Physiology of the Nervous System. New York, Oxford Medical Publications, Ox­

ford University Press, 1943, pp. 57-59, 331, 493, 501. 4. Hilgard, E. R., and Marquis, D. G. : Conditioning and Learning. New York, Appleton-Century

Co., 1940, pp. 310-336. 5. Lancaster, W. B. : Ocular motility. Am. J. Ophth., 24:485, 619, 741,1941. 6. Pavlov, I.: Lectures on Conditioned Reflexes. New York, International Universities Press, 1928. 7. Sherrington, C. S. : Integrative Action of the Nervous System. New Haven, Yale University Press,

1906, p. 20.

DISCUSSION OF MISS EYLES' PAPER

GEORGE S. CAMPION, M.D. San Francisco, California

The neuron component of the ocular-muscular apparatus has been somewhat neglected in our work because it is so poorly understood even by those best qualified to explain it to us. I think Miss Eyles has done an excellent piece of work in bringing together the many intangibles that form the basis of our present knowledge of how fusion is attained, and it is only by a sound knowledge of the physiology of vision and the associated neuron-anatomy that we can understand how fusion is made possible or impossible.

We must try to assign the most exact etiologic factor possible to each case of squint for if we are able, by a good history and a thorough examination, to find the

etiology, we are well on the way to a com­plete physiologic cure.

True, some etiologic factors cannot be found and others cannot be removed and remain as permanent barriers. Still other barriers may be removed only after diligence and perseverance in the best of teaching techniques.

How diligent can you get? Certainly training should go on until all removable barriers are removed and the teaching phase given an intensive trial. For orthoptics be­comes a teaching process only when there are two good eyes that are reasonably matched one to the other and an I.Q. high enough to learn new skills or relearn neg­lected skills.

1152 GEORGE S. CAMPION

As Miss Eyles has mentioned, if we as­sume there is a fusion center at some corti­cal or subcortical level we make everything very simple. Then, in the absence of a recog­nizable physical defect or recognizable func­tional defect, we can place failures into a comfortable fusion-defect group, dismiss them and work on the easy ones.

In the early days of orthoptics this group was a very large one, but it is dwindling in the face of better teachers and better tech­niques. I do not think the group will en­tirely disappear, but it will no longer be the wastebasket to catch all the failures from either side of the machine.

Most of the fusion-difficulty cases in those acceptable for training seem to occur in that group of alternators who had an early onset of squint—that is some time before the age of two—and who have been neglected. Many have had absolutely no fu­sion experience and have to be taught every­thing artificially. Their barriers to fusion are a fixed angle of squint, anomalous cor­respondence, deep alternating suppression, and complete comfort in their monocular world. The deviation should be corrected surgically in this group as early as possible, even before the child is capable of perform­ing some of the tests you would like to do.

Nothing is gained by waiting until he is capable of being tested for the deviation will have to be corrected in any case. The child is incapable of straightening his eyes—a mechanical barrier—even though he learns skills all the way up the binocular ladder.

If such an alternator is first seen at the age of 6 or 7 years, then preoperative train­ing may be given to good effect if the angle is not so large as to make training all but impossible. In this latter case the last barrier to be removed will be the mechanical one of heterotropia and, needless to say, training should follow surgery as soon as possible and be as intensive as necessary to obtain binocular vision with fusion for casual seeing and reading.

Miss Eyles has pointed out that one small patient may harbor a whole nest of barriers to fusion, and it is fortunate that sometimes we can remove two barriers at once. Anti-suppression exercises are the same, basically at least, as antianomalous exercises and what a surprise occasionally is met when the surgical correction of a heterotropia also abolishes the anomalous correspondence.

Were I to be given a single choice of the many aids to fusion I would choose a good technician.

490 Post Street (2).