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THE RELATION OF HEREDITARY EYE DEFECTS TO GENETICS AND EUGENICS (1)

Lucien Howe, M.D., Buffalo

OF LATE years, while trying to learn something about ocular muscles, I have been confronted often by questions concerning heredity. I have found, as others doubtless have, three, four or even more persons in the same family with a similar form of heterophoria, (2) heterotropia, (3) predisposition to ocular fatigue, or similar abnormal muscular conditions. It seemed impossible to study these anomalies satisfactorily without first halting to learn something about that mystery which we call heredity.

(3) Displacements in position.

It is not possible here to give any systematic account of the studies al- ready made of hereditary eye defects, except to mention the classic work by Groenouw, (4) the interesting histories collected by Nettleship, the more recent bibliography by Loeb, with the exhaustive articles by him, or those by Libby and others. The point is that we ophthalmologists have been content thus far with reporting family histories without attempting to relate those histories to other facts, now well established by geneticists.

The best way to learn these principles, and one vastly more interesting, is to supplement the reading with at least a few experiments.

The breeding of eye defects is easier than most persons imagine. Chickens and pigeons are the best subjects for such experiments.

By advertising in the Reliable Poultry Journal and other trade papers, it has been possible to obtain for the parent stock more than a dozen specimens of eye defects. These included corneal irregularities, and variations in the color of the iris and in the position of the eyes and of the pupil. The different pens of chickens at a small place, known as Mendel Farm, on the lake shore near Buffalo, have proved to me a source of much interest and enlightenment.

The breeding of dogs has not been found satisfactory. Eye defects are rare, the generations slow and the litters small. For similar reasons, cats are undesirable. It is probable, however, that interesting results could be obtained by breeding white cats which have blue eyes -- such cats being often deaf. This fact had been already observed by Darwin and has been the subject of breeding experiments by Dr. Graham Bell. (5)

The eyes of the small fruit fly, Drosophila ampelophila, have proved most interesting. I am indebted to Professor Morgan of Columbia for parent stock, the blind variety of which I bred through more than twelve generations.

PRACTICAL VALUE OF THE STUDY

The average reader of this paper may say that such a glance at the principles of heredity may be curious and possibly interesting, but of what practical use is it?

Of course we never find a typical Mendelian ratio in the human species, because brothers and sisters never marry. (6) But an approach to these ratios we do find constantly, and that law furnishes an important guide, not only in recognizing heredity itself in a given family history, as distinguished from an infection, but in also indicating when the defect is dominant or recessive. In other words, this relation between genetics and ophthalmology throws light on the differential diagnosis (the next step in our study), and is very decidedly practical in connection with eugenics.

With this reassurance as to the reason for continuing, let us pass to the examination of family histories to determine whether a given defect is in reality hereditary, or whether it is due to infection from syphilis or other causes.

It would necessitate a rather long digression to show just how this differential diagnosis is made. Suffice it to say that our criterion is the technical definition of heredity given at the outset. The fact is that a very considerable proportion of defects which we all supposed formerly were hereditary are probably not hereditary, but the effect of some infection more or less obscure. An excellent example of this is a family history of aniridia reported by one of the oldest and best known members (7) of this section. The author and all other ophthalmologists accepted this as an undoubted example of heredity, but competent geneticists now demonstrate that to be highly improbable.

The term "hereditary" we should also define more exactly as including two groups -- one in which the recurrence of the defect is only "possible," especially when that defect is "recessive," the other in which its recurrence is "probable," especially when that defect is "dominant." Evidently, therefore, we have as many conditions to deal with as there are combinations, in pairs, of these four factors.

Still another factor enters into the problem -- the personal equation of the parties to a marriage contract. For when two persons contemplate matrimony, it can usually be taken for granted that their judgment has, for the time, taken wings. Professor McCready, in his lectures at the College of Physicians and Surgeons, used to say his case records showed that for various reasons he had advised one or both parties against marriage some sixty-eight times; and his records also showed that sixty-eight times the couples went almost straight to the altar.

But temporary obsessions by those who ask an opinion is no excuse for inability to advise intelligently, or, if necessary, to restrain persons from a fatal mistake. Therefore the other four factors in our problem demand all the more careful study. While the difference between a simple deformity and blindness is evident, it is not easy to say whether the recurrence of a given defect is "possible" or "probable." Our decision, then, must be based on three groups of data: first, whether the defect is inherited as a dominant or a recessive; second, whether it is a sex-linked characteristic, and, third, whether both families show the defect.

A few illustrations will show how these four cardinal conditions in our problem may serve as the basis for an opinion by an ophthalmologist when he is called on to give advice in the case of a proposed marriage. Thus:

(a) When we have to do only with a deformity, and its reappearance is doubtful, no special objection need be raised.

(b) When we have to do only with a deformity, and its reappearance is probable, the parties to the marriage should both be warned of the probability of the reappearance of that defect in their offspring.

(c) When we have to do with blindness, and its reappearance is doubtful, a stricter attitude toward the union can be assumed.

(d) When we have to do with blindness, and its reappearance is probable, the question assumes its most serious aspect. If the family history shows that this defect is in reality dominant, then half the children on the average will develop the defect; or even if the defect is recessive, but occurs in both families, the danger is practically the same.

Another phase of the same problem is presented when a couple is already married, and with little or no history on either side of eye defect; yet in spite of that, for reasons which we do not know, one child after another, blind or partly blind, is born to these parents. This congenital blindness is in one way quite different genetically from hereditary blindness, but from the standpoint of eugenics, families with hereditary and with congenital blindness may be considered together as one group and classed as hereditary. It is desirable to appreciate how important this group is, but space permits here only the categorical statement of a few facts, which, properly presented, would fill a small volume. These facts are:

(a) The number of this group in the United States is considerable. It has been estimated at about 8,000 and upward. According to the census of 1910, the total number of blind was 52,272. Counting unavoidable and ad- mitted errors in that census, the results of subsequent surveys, and increase of population, the National Committee for the Prevention of Blindness estimated the number of blind in 1917 at from 100,000 to 110,000. According to the data given by Best in his exhaustive and recent study of the blind in this country, the proportion of hereditary and congenital blind is considerably larger than here stated. But in giving estimates, the minimum limit is evidently the safest.

(b) The cost also is considerable. According to statistics carefully collected in Massachusetts and elsewhere, the average cost per year of each blind person in and out of institutions is at least $475. This gives us a total annual cost of some $3,800,000.

(c) It is unjust to the blind to allow them to be brought into existence simply to lead miserable lives.

(d) It is unjust to taxpayers to be compelled to support them.

(e) The longer we delay action to prevent this blindness, the more difficult the problem becomes.

(f) A large part, if not all, of this misery and expense could be gradually eradicated by sequestration or by sterilization, if the transmitter of the defect preferred the latter. An idea of this plan is given by the somewhat similar one for dealing with feeblemindedness. In 1913, laws for sterilization, under certain circumstances, had been passed in twelve states and proposed in nine others. Bulletin 10 of the Eugenics Record Office, Cold Spring Harbor, L. I., N. Y., gives a map showing the status at that time of such legislation. Where such eugenic laws have been enacted or favorably considered, probably existing laws could be properly amended or new laws passed to prevent this form of blindness. The same bulletin gives the form of a model law for this purpose. It was prepared by committees composed of the most eminent physicians, surgeons, sociologists, students of genetics and similar experts in this country. That law could be made applicable to the prevention of hereditary blindness, but with an important difference, which makes the prevention of this form of blindness comparatively easy and inexpensive. No legal action is essential until after a marriage has been found to produce blind children, and even then sequestration of the transmitter of the defect may be substituted for sterilization. Moreover, if this sequestration is of a kindly nature, with congenial occupations suited to the intelligence and social tastes of the subject, the sense of restraint is slight, since it is reduced to the minimum. This is not theory but experience, as shown especially by the colonies for the feebleminded established by Dr. Charles Bernstein of the State Custodial Asylum at Rome, N.Y.

WHAT ARE WE GOING TO DO ABOUT IT?

In other words, we have all this misery and expense, both of which are largely unnecessary; we have also an effective method of relief prepared by committees of our foremost experts and already well supported, in principle, by public opinion. What are we going to do about it? That is the question at last forced on ophthalmologists -- especially on the Section on Ophthalmology of the American Medical Association. Shall we complacently continue to do nothing, thus retarding social advancement and even ophthalmology itself? The answer to this question involves many details, both of principle and of method, far too complicated for discussion now. But in executive session a motion will be made for the appointment of a committee to report on this subject another year. (8) If at that time or later, some plan can be formulated for the prevention of this form of blindness, it will perhaps seem worth while for us to have directed our attention now, even in this hasty manner, to the relation of hereditary eye defects to genetics and eugenics.