141 In 91 out of 102 cases in Mr. Hutchinson's series—in 6, the left alone; in 5, the right alone (op. cit., p. 123).
When the height of the disease is reached the corneæ are nearly opaque, a bare perception of light remaining, so that the patient is just aware of the difference between its presence and absolute darkness. Then the cornea which was first involved begins to clear; this is soon followed by improvement in the other one, which in the course of a year or two results in a return to fairly good sight, although in most cases there remain a slight haziness and an abnormal expansion of the cornea.
This favorable result is much influenced by the character of the case, which is sometimes very mild from the outset, and by the thoroughness of the treatment. It is sometimes complicated with iritis, kerato-iritis, cyclitis, posterior choroiditis, secondary glaucoma, etc., in which cases of course the prognosis is most unfavorable. Even in ordinary cases it should be guarded in respect to perfect restoration of function, as clearing of the corneæ may reveal adhesions from iritis or spots of choroiditis disseminata, which could not, of course, have been previously detected. In very mild cases, however, without much evidence of involvement of the other tunics, and which have been submitted to treatment early, it is not uncommon for the cornea to regain almost perfect transparency.
The diagnosis of this condition may generally be made with ease. The ground-glass appearance in the earlier stages and the dull pink or salmon color in the more vascular stage are very characteristic. The vascularity differs from that attending other chronic forms of keratitis, granular lids, etc., in which the vessels are large and superficial, in that in the syphilitic keratitis they are much deeper and very closely interwoven, so that the effect is almost that of an ecchymosis. In other cases both eyes are not so apt to be affected, nor is the tendency to spontaneous cure so marked. The absence of ulceration and the very slight degree of accompanying sclerotic or ciliary congestion are also valuable features.
The conditions which Mr. Hutchinson has known to be most frequently mistaken for it142 are certain forms of inflammation following small-pox and very superficial ulcers in a healing stage, together with cases of vascular conjunctiva.
142 Op. cit., p. 128.
There is also said143 to be some difficulty in distinguishing it from a form of non-syphilitic relapsing cyclitis with corneal opacities and iritis. This, however, is a disease of adults, often limited to one eye, with a strong tendency to relapse, the opacities being more abruptly defined and limited to the region near the circumference.
143 Edward Nettleship in Hill and Cooper, op. cit., p. 267.
The chief point of interest, however, in the diagnosis of interstitial keratitis is its association with other symptoms of syphilis, upon which, for the general practitioner at least, the diagnosis will usually depend.144 Mr. Hutchinson's conclusions, drawn from an analysis of 102 cases of interstitial keratitis, bear strongly upon this point, and are as follows:145 A large proportion of all cases occur in patients between the ages of eight and fifteen, the disease being comparatively rare in early childhood, and still more so after adult age has been reached. He never saw it begin after the age of twenty-six. The patients presented the physiognomical peculiarities of inherited syphilis (see p. [313]). In more than half the cases the previous history, especially as regards infancy, was one of hereditary syphilis, and in many instances there was a clear history of infantile syphilis in brothers or sisters. In half the cases no questions were asked as to the existence of venereal disease in the parents prior to the birth of the child. In 29 out of the other half such disease was freely admitted. All the patients had lost in early life nearly half their brothers and sisters. Omitting miscarriages and premature births, it was found that 77 mothers had borne 547 children, of whom only 284 remained alive—an excessive rate of mortality. It appeared in the large proportion of cases in the eldest children in their respective families—a circumstance to be expected in view of the usual behavior of hereditary syphilis in families. Undoubted syphilitic lesions, such as nodes, ulceration of the palate, etc., are not infrequently associated with the keratitis.
144 "To those who have not had opportunities for observation at an ophthalmic hospital I would recommend that the diagnosis should be held to be doubtful if the patient does not present the peculiarities of teeth and physiognomy which I have described, since we find that the latter are the almost invariable concomitants of the true disease" (Mr. Hutchinson, op. cit., p. 128).