Heterochromia

HETERCHROMIA (from Greek heteros- other, different and chroma- color), different color of eyes, depending on the different coloration of the iris of one and the other eye. The coloration of the iris is in close connection with the general pigmentation of a given individual (color of skin and hair), and as a rule both eyes have not only the same color but also the same tone. Abnormal pigmentation of the iris, by the law of contrast, catches the eye of both the patient and the physician only when it affects one eye, i.e., when there is so-called heterochromia iridis. Usually two main types of iris color are distinguished - the light (mostly gray-blue of various shades) and brown (light and dark brown), which depends mainly on the amount of pigment of both uveal and retinal origin. But both types differ not only in color but also in the consistency of the stroma itself and in the relief of the anterior surface of the iris. As is known, of all the membranes of the eye, the iris shows the greatest individual differences in color; and with the introduction of a new method of studying it with the help of living microscopy, we are more and more convinced that there are no ideally identical irises in the same person (in terms of the quantity and symmetry of pigment distribution), and therefore the view of what should be called heterochromia of the iris must somewhat change. Heterochromia can form in two ways: either by insufficient development of pigment in one eye or by subsequent depigmentation. The different coloration of the eyes is not established immediately after the birth of a child, but somewhat later, and therefore the delay in normal physiological pigmentation is not immediately noticed. Streiff is very skeptical about the subsequent depigmentation of the iris in congenital uncomplicated heterochromia and is rather inclined to assume unilateral heterohyperchromia or melanosis iridis. He believes that true depigmentation of the iris can arise only on the basis of trophic vasomotor disorders. Different pigmentation of the iris is also in close connection with the hereditary factor, i.e., hereditary crossed coloration of the iris (Lutz, Steiger and others). In such cases, one eye will be of the mother's color, the other of the father's color, in connection with the transmission of a number of parental traits according to Mendelian laws of heredity. Therefore, it would be more correct if primary uncomplicated heterochromia (such as melanosis iridis, iris bicolor, naevus iridis pigment, etc.) is not classified as true heterochromia (secondary), developed as a result of various pathological conditions of both the eye and the entire organism, but is considered only as an expression of direct crossed monolateral hereditary asymmetry. Heterochromia due to a number of intraocular and general diseases is also of particular interest, such as: iritis, choroiditis, glaucoma, hemorrhages, siderosis, leukiridic syphilis, xanthomatosis iridis, etc. Even if the difference in coloration of the iris of both eyes in this group of cases seems at first glance to be the most outstanding symptom, however, further careful studies always make it possible to establish the underlying disease. Thus, of greatest interest are: first, the true complicated so-called Fuchs' heterochromia, described in detail by the author as early as 1902, and second, sympathicus-heterochromia, which is attracting more and more attention. As early as 1869 Hutchinson pointed to cataract as a complication of the light heterochromatic eye, and then this complex and interesting question was studied by a number of authors. It has been noted that in persons who have different coloration of the iris, cataract develops in the lighter eye over the years, along with cyclitis and deposits of point-like sediments on the posterior surface of the cornea. In individual cases heterochromia exists from early childhood, in other cases patients note this fact only in later years, possibly only with the onset of decreased visual acuity, and finally, in a number of cases patients indicate gradual discoloration of the iris of one eye without any connection with general diseases. Among patients, brunettes and dark-eyed individuals are observed as often as blondes and light-eyed individuals. According to some authors, blue-eyed individuals are noted somewhat more frequently. Lifestyle and sex have no influence on this disease. The age of patients, according to all authors, is most often between 20 and 45 years. Clouding of the lens, point-like and streak-like, usually begins with the posterior cortical layers. The color of the lens is bluish-white, with a clearly expressed sector pattern. The nucleus is small. Clouding of the vitreous body - in the form of small, more or less coarse separate flakes. In addition, the precipitates that usually exist with such heterochromia can sometimes be noted only with great magnification as delicate, separate, in small numbers scattered, white sharply outlined spots on the posterior surface of the cornea, never merging with each other and not giving large dense deposits. The microscopic picture of such a changed iris is especially characteristic. In addition to the difference in color, depending on the decrease in stromal pigment, the entire surface relief of the discolored iris always seems more or less blurred. Radial trabeculae in the pupillary area do not protrude so sharply, crypts are smaller, there is no clear translucence between individual trabeculae of the retinal pigment layer, vascular trabeculae and vessels are not sharply outlined. The entire iris therefore has a dull, flaccid appearance, but at the same time there are no fresh inflammatory changes in it, no exudates and posterior synechiae. In the retinal pigment layer, in most cases, only subsequent defects of the pupillary edge of the iris, its narrowing and notching are noted. The eye is usually completely calm, there is no photophobia, and only in exceptional cases is there a barely noticeable ciliary injection of vessels. The unusually slow and imperceptible development of the disease easily explains the fact that different authors interpret the three main symptoms of the disease differently: heterochromia, cataract and cyclitis. However, all agree that the main thing is not the depigmentation of one iris, but that mysterious process in which, along with congenital anomalies (such as coloboma of the iris and choroid, microphthalmus, nystagmus, etc.), chronic changes of a purely inflammatory nature are also noted (e.g., in violation of the normal circulation of fluids in the eye, abnormalities of internal secretion, various vascular disorders and even tuberculosis). In any case, the question of the connection between depigmentation of the iris and inflammation, as well as the nature of the inflammation, in the heterochromia described above remains open to this day. As for the prognosis and treatment, the only possible measure in such complicated heterochromia should be considered the extraction of cataract, which often occurs without any complications. The prognosis for such an eye in general is doubtful. Neur sympathicus-heterochromia is currently of particular interest not only among ophthalmologists but also among neurologists and internists (this disease was described by Fuchs, Curschmann, Kaufmann, Metzger, Monyukova, Roshchin and others). That diseases of visceral organs can be reflected in the most distant parts of the body is a fact already generally recognized in medical literature. Such a distant symptom in some internal and nervous diseases is also the difference in pigmentation of the iris. Neur heterochromia is accompanied in all cases by completely normal function of the light eye, without any deposits on the posterior surface of the cornea, clouding of the lens and vitreous body. The microscopic picture of the iris shows only a decrease in stromal pigment compared to the other eye, with a sharply outlined relief of the anterior surface and well-expressed trabeculae and crypts. The pigmentation of the iris is approximately uniform in all its parts. The movements of the trabeculae are not disturbed. Neur heterochromia is characterized only by more or less pronounced phenomena of paresis of the sympathetic nerve on the side corresponding to the discolored iris. Kaufmann and Metzger also connect neur heterochromia with a unilateral condition of increased irritation of the cervical sympathetic ganglion. In this respect, the mentioned neur heterochromia should be considered as a consequence of asymmetric tone of sympathetic innervation both in terms of decrease and increase. How the sympathetic nerve influences the development of the anterior boundary layer of the iris and its pigment remains to this day not exactly clarified. Heterochromia is in any case a serious indication of the presence of certain changes in the complex apparatus of the vascular and nervous systems. Against the recognition of partial albinism as heterochromia (Laubert, Peters, Lutz) speaks, first of all, that albinism is a general disorder in the formation of pigment and therefore affects equally both mesodermal and retinal pigment, while heterochromia is limited only to one mesodermal pigment of the iris.

Secondly, albinism as a rule does not give any complications to the eye, and, thirdly, albinism is a familial, hereditary anomaly of pigment development.