Howe''s article in the Journal of the American Medical Association gives a synopsis of the current state of knowledge on the Mendelian inheritance of eye disorders and the costs of caring for the hereditary blind. There is also a discussion at the end of the article including

316. 1996 Hereditary Eye Defects Journ. A. M. A. June 27, 1918 It is impossible in a brief statement like this to give even passing notice to other principles of heredity which are of undoubted importance in a study of eye defects. Among these may be mentioned blended and excessive inheritance, reversion, predisposition to disease, immunity, etc. But it is doubtless the case that even our present knowledge of these principles will assist us in understanding why in certain families this or that defect of the eye does appear to be dominant, and on the other hand, why in certain other families the same defect to be more distinctly recessive. Thus by charting the knowledge which we have thus far acquired of eye defects and comparing those charts with a knowledge of the principles of heredity, it is probable that the relation between the two will become more apparent. Approach to the Study by the Ophthalmologist One of my main objects, as already stated, is to interest others, if possible, in this subject, so that they may help to solve questions that can only be hinted at here. Therefore, it is in order to indicate briefly how the study can be approached by any ophthalmologist. As to a theoretical knowledge of heredity, it may be of assistance to mention a few books which have been found useful. Herbert's "First Principles of Heredity" gives an outline of the entire subject. Castle's "Genetics and Eugenics" is more elaborate and technical. Davenport's "Heredity in Relation to Eugenics" is especially interesting and gives a number of data relating to hereditary defects of the eye. A short, systematic course of reading like this gives a theoretical idea of the principles of heredity sufficiently definite to enable the ophthalmologist to discern some of the relations between a given principle or line of descent and a given group of eye defects. Theoretical knowledge is, however, second hand mental furniture. 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 often being deaf. This fact had been already observed by Darwin and has been the subject of breeding experiments by Dr. Graham Bell[superior]3[end superior]. The eyes of the small fruit fly, [ital]Drosophila ampelophila[end ital], 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. 3. Bell, Graham: Tr. Otol. Soc. [illegible]. 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. 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 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[superior]4[end superior] 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. Other diseases besides syphilis, or susceptibility to them, undoubtedly are transmitted from parent to offspring, and with these diseases we should include the effects of alcohol. In a word, caution is necessary in our diagnosis. We find, too, that even many of the muscular anomalies which seemed to be hereditary, and which prompted this whole study, are not hereditary after all. Having thus collected various family histories, even those said to be hereditary, classified them, added to their number, charted them, studied the relation of genetics to those histories, and having seen the necessity of more exact diagnosis, we can now leave this imperfect sketch of the relation of eye defects to genetics, and pass to the eugenic aspect of this subject. The literature concerning this is scanty and confused. It will tend to clearer thinking to define a few terms. From the standpoint of eugenics, eye defects may be divided into two groups - the minor defects, or deformities, and major defects, or blindness. 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 judg- 4. Ridey, S.D.: Hereditary Aniridia, The Journal A.M.A., April 17, 1913, p. [illegible].