Anatomy.-The choroid is that portion of the uveal tract extending from the ciliary body backward to the optic nerve. It lies between the retina and the sclera and is principally composed of blood-vessels and pigment. The choroid may be considered the nutrient membrane for the interior structure of the eyeball, and consists of four layers. The outermost layer is composed of loose connective tissue and of irregular shaped pigment cells; these connective tissue fibres extend into, and are derived from, the sclerotic, and the meshes of these fibres form spaces conveying lymph.
This lymph space is held to be in direct communication with that of the capsule of Tenon and the other lymph-spaces of the eyeball. In separating the choroid from the sclera, these fibres are necessarily torn, and that portion remaining adherent to the choroid has been termed the lamina supra-choroidea, and that part remaining attached to the sclerotic, the lamina fusca. The next layer is that of the tunica vasculosa-a layer of large blood vessels which forms a large portion of the parenchyma of the choroid. The third layer, known as the chorio-capillaris, is made up of the finer branches or capillaries of the arteries and veins of the tunica vasculosa.
These two layers, together with a small amount of connective tissue, some elastic fibrillae, and cells, both pigmented and unpigmented, form the parenchyma of the choroid. The blood supply of the choroid (see Fig.65) is chiefly derived from the short posterior ciliary arteries, which pierce the sclerotic obliquely and enter the choroid and branch off, anastomosing with the long posterior and the anterior ciliary arteries. The veins, beginning as capillaries in the chorio-papillaris, take, in the tunica vasculosa, a whorl-like form and uniting into from four to six large trunks called the venae vorticosae, pass obliquely through the sclera at about the equatorial region of the eye and empty in the ophthalmic vein.
A small amount of the blood from the anterior part of the choroid passes out through the anterior ciliary veins. The parenchyma of the choroid also contains a great many nerves coming from the short and long ciliary nerves and which form in the choroid fine plexuses of nerves with many ganglionic cells. The most internal layer of the choroid is called the lamina vitrea or elastica. It is an elastic and perfectly transparent membrane, upon which the (uveal) pigmented epithelium lies. This pigmented epithelium, lying between the choroid and retina belongs to the latter but remains attacked to the choroid when the retina is removed from the eye. Nearly every pathological condition of the choroid exerts an influence upon this layer of pigment, while important changes are apt to occur in the retina without any alteration in these pigmented epithelial cells. As it is anatomically a part of the retina, we will consider its further description under that membrane.
Hyperaemia of the Choroid.-Owing to the general continuity of tissue with ciliary body and iris, and to its excessive vascularity, the choroid is necessarily very apt to become hyperaemia from almost any inflammatory changes of the eye. In fact, hyperaemia of the choroid undoubtedly is present more often than is generally recognized. The diagnosis is difficult to make on account of the pigment layer in front of it, and is especially so in dark people. In blondes and albinos the choroidal vessels may be seen and the diagnosis aided. The only symptoms, however, of diagnostic value are a diffuse hyperaemia of the optic disc and a woolly appearance of the pigment layer. Hyperaemia of the choroid is distinguished from a hyperaemia of the optic nerve and retina by the fact that in the former the redness of the disc is diffuse and its outlines are sharp and well defined, while in hyperaemia of the nerve and retina the outlines of the disc are ill defined and the redness has more of a striated appearance. The treatment is detailed under that of choroiditis in general.
Choroiditis.-The appearance of the healthy choroid must first be carefully studied before one can fully appreciate changes, whether inflammation or otherwise, of its structure. The color of the fundus of the eye, when examined with the ophthalmoscope, varies in different individuals according to the amount of pigment granules contained within the pigment or uveal layer. In fair persons we find the fundus appearing of a yellowish-red color and the vessels of the choroid can usually be plainly seen (See Chromo Lithograph, Plate, 11, Fig.1.); in darker persons and negroes the color varies from a brownish red to a slate color and the choroidal vessels are entirely hidden by the pigment layer. The color and intensity of the light used and the extent of the dilatation of the pupil also serve to affect somewhat the color, of the fundus.
Great alteration may take place in the choroid and nothing be discernible; in fact, in some cases it is only when the retinal pigment cells have become affected by the pathological process that ophthalmoscopic changes are observed. Hence, characteristic appearances of choroiditis are only seen when the retina has become affected as well; that is, when the disease has become a choroido-retinitis. Clinically, however, the disease is still a choroiditis, even though the outer layer of the retina has become secondarily affected. In choroiditis the eye shows no external evidence of disease (except in suppurative choroiditis), and is only manifested to the patient by a loss of vision and to the physician by the ophthalmoscopic appearance. Inflammation of the choroid may be the same as in other divisions of the uveal tract, of a serous, plastic purulent type.
Choroiditis Serosa.-Is considered by some authorities as a form of glaucoma. The consideration of serous inflammations of the uveal tract is a subject of great disagreement among the various authorities. We have referred to each disease separately because each division of the uveal, the iris, ciliary body, and choroid are certainly susceptible to separate involvement by other pathological processes, and we cannot conceive why there may not be a serous inflammation of either structure alone. As a rule, however, we usually find a serous inflammation involving the choroid, ciliary body and iris at the same time, and while it may commence in one structure it probably rapidly extends to the others and perhaps should more properly be termed a serous uveitis. As the cornea is also usually affected in serous uveitis, it may be that the disease described as descemetitis is merely a manifestation of the similar process in the cornea through a direct extension by continuity of tissue.
PATHOLOGY.-There is at first a general or localized hyperaemia, especially affecting the veins of the choroid. Following the hyperaemia there is either serous or sero-fibrinous exudation, which is found extending inward either into the pigment layer of the retina, between the retina and vitreous, or into the vitreous body itself. The increased secretion of a serous fluid within the eye may, when the channels of excretion have become altered or obliterated, result in glaucomatous symptoms.
SYMPTOMS.-There may be slight ciliary injection and the dotted appearance of the cornea, as in serous iritis. The aqueous and vitreous humors are slightly hazy, causing a general indistinct and hazy appearance of the fundus. Fine floating opacities may be discovered in the vitreous and vision is impaired in proportion to the opacity of the media. The tension should always be examined, as it is very liable to become increased and glaucomatous symptoms set in. Serous choroiditis seems often to be associated with syphilis, rheumatism or gout, and generally occurs as a complication of serous iritis.
The treatment is the same as with other inflammations of the choroid, but the use of remedies, especially Gels, and Bry, is very essential.
Choroiditis Disseminata Simplex.-Simple disseminated choroiditis is of the plastic form of inflammation.
PATHOLOGY.-Plastic choroiditis, never attacks the whole choroid, but takes place in small patches, which may coalesce and grow larger. The hyperaemia in this form is followed by a fibrocellular exudation into the stroma of the choroid, and we find numerous small nodules composed of a fibrinous substance and round cells. There is also a lymphoid infiltration along the vessels, which makes them appear as yellowish-white striae. The retina and pigment layer at this stage are normal, or only slightly elevated by the underlying infiltration. Absorption may take place at this stage, leaving the stroma of the choroid normal. If the process goes on there is a proliferation of the pigment layer over the nodules, the exudation presses more and more upon the retina, the layer of rods and cones become involved and the tissue of the retina is affected. The proliferation of pigment extends into the external granular layer, and, when the exudation extends deeply into the retina, the radial fibres of the retina run into the exudation and become united with the fibrillated, structure of the nodule. In the later stages the cell elements gradually disappear and the fibres retract, leaving a depressed retinal scar. The cells covering the exudation lose their pigment and may be totally destroyed. Their pigment, having thus been freed, is taken up by the cells at the periphery of the patch of exudation, and then we have the characteristic white atrophic spot surrounded by a dark pigmented border.
Professor of Ophthalmology in the College of the New York Ophthalmic Hospital; Surgeon to the New York Ophthalmic Hospital. Visiting Oculist to the Laura Franklin Free Hospital for Children; Ex-President American Homoeopathic Ophthalmological, Otological and Laryngological Society. First Vice-President American Institute of Homoeopathy : President Homoeopathic Medical Society of the State of New York ; Editor Homoeopathic Eye. Ear and Throat Journal : Associate Editor. Department of Ophthalmology, North American Journal of Homoeopathy, etc.