Anatomy.- The cornea is nearly circular in shape, though slightly more prominent in youth than in old age. It is perfectly transparent and this transparency is due to the arrangement as well as the individual transparency of each of its constituent elements. The cornea is composed of five layers which, taken from without inward, are the anterior epithelial layer, Bowman’s membrane, the substantia propria, Descemet’s membrane and the posterior endothelial layer.
The anterior epithelial layer is like the epithelium in other parts of the body, though in this location it is composed of from six to eight layers of cells, varying in size and shape, with nuclei and nucleoli, the innermost ones having offshoots. This epithelium is more transparent and thicker, but continuous with that of the conjunctiva.
Bowman’s membrane is simply a layer of corneal cement containing fibrillae and fasciculi, but with no lacunae or lymph canals, and therefore, has neither fixed cells nor movable corpuscles. It is closely adherent to the cornea proper and cannot be separated from it as a distinct layer.
The substantia propria is made up of extremely fine connective tissue fibrillae united into fasciculi. A cement substance binds the fibres and fasciculi together. There is a system of spaces, lacunae, and lymphatic canals, canaliculi, which are a continuation of the lymphatic vessels and spaces. The corneal cells fill these lacunae and their branching arms the canaliculi.
The fibrilloe and fasciculi of fibres are disposed in layers one above the other, forming in this way a structure made up of lamellae, about sixty in number.
The cement is a homogeneous substance binding the fibres and fibrillae together.
The corneal spaces are hollowed out of the compact tissue formed by the cement and the fasciculi arranged in lamellae and are composed of numerous lenticular-shaped shallow spaces communicating together by offshoots or canaliculi. These spaces have no proper lining and vary in size. They run from one layer to another and even penetrate between the fibres, thus forming a network throughout the corneal tissue. The canals convey the lymph for the nourishment of the cornea and the spaces contain the cells of the cornea, which are of three varieties-the fixed cells or corneal corpuscles, the migratory and the pigment cells.
The fixed cells lie in the lacunae, are flattened, have both nuclei and nucleoli and send prolongations into the canal.
The migratory cells are distinguished from the fixed by their large and variable size, their brilliancy and the power of motion. They correspond to leucocytes and increase in number during inflammation.
The pigment cells are similar to the fixed cells, found only at the periphery of the cornea and are especially present in negroes.
Descemet’s membrane is the inner lining of the parenchyma. It is a structureless, homogeneous membrane, of a glassy appearance and highly refractive. It is firm and elastic, and is supposed to be a condensation of the cement substance of the cornea proper.
The endothelial layer consists of a single layer of endothelial cells lining the posterior surface of the membrane of Descemet. The cells are flat and of varying shape and distinctly nucleated. At the periphery of the cornea this layer is reflected upon the ligamentum pectinatum iridis and thence upon the anterior surface of the iris.
Blood-vessels are only found on the outskirts of the cornea and are derived from the anterior ciliary arteries.
The nerves of the cornea, about forty in number, penetrate its tissue, lose their medullary sheath, become transparent and divide dichotomously to form large plexuses, which ultimately end in a fine plexus beneath the anterior epithelium. From this subepithelial plexus fibrils are given off which pass among the epithelial cells.
Inflammation of the Cornea may be either primary or secondary to inflammation of other tissues. It may induce inflammation of the adjacent structures, such as the conjunctiva, iris, ciliary body, etc., or it may exist with inflammations of these structures.
Inflammation of the cornea is diagnosed by increased ciliary injection, a decreased transparency, a loss of lustre of the cornea or ulceration. Vision is more or less disturbed, according to the location of the inflammatory foci, by the dispersion, absorption or irregular refraction of light. Keratitis is perhaps one of the most frequent diseases of the eye; it is also, considering the function of the eye, one of its most important affections. It endangers the function and also the form of the eye in many ways, viz.: by causing incurable opacities, by a permanent change in its convexity, by perforation and its sequelae; by inducing iritis, irido-cyclitis, etc.; by destruction of a portion or the whole of the cornea; by destruction of the form of the entire globe, as in staphyloma, phthisis bulbi, etc., or again, keratitis may run its course, leaving no bad results.
The classification of corneal diseases is as varied as the different writers upon this subject, each new author seeming to strive for some new name or sub-division to cover different types of the same disease. We have selected to follow in a general way the classification of de Wecker as being in our opinion the simplest and most practical.
Keratitis Phlyctenularis.-Eczema Corneae, Scrofulous, Strumous, or Pustular Keratitis.)
PATHOLOGY.- Consists of a circumscribed infiltration of leucocytes into Bowman`s layer. This infiltration is always confined to the parts surrounding a nerve-branch as it pierces the epithelial layer. This simple local infiltration generally results in local purulent keratitis, with a loss of substance and the formation of a scar.
SYMPTOMS.-We will first notice small, grayish elevations upon some part of the cornea, usually the periphery, varying in size-perhaps, as a rule, about one-half the size of the head of a pin. There may be one such elevation or a row of them extending around the cornea. There will be a redness which may encircle the entire cornea, or more often, where there is but one phlyctenule, confined to the quadrant of the eye affected and assuming a more or less triangular shaped injection, the apex of which will be at the point of infiltration. The conjunctiva is often more or less inflamed, may be swollen and secretes a muco-purulent discharge. The photophobia is often so intense that the child will bury its face away from the light and it will be found difficult to open the eye for examination. Again, other cases will be met with in which there is not the slightest photophobia. The appearance of the vesicle is generally preceded or accompanied by a sense of heat and itching in the eyelids, lachrymation and ciliary neuralgia. Sometimes the phlyctenules are very superficial and appear as small, transparent vesicles, whose epithelial covering is soon shed, leaving a small excoriation which may easily escape detection. Generally, however, the infiltration is more apparent and is surrounded by a zone of opaque and swollen cornea; the apex breaking down, it extends in circumference and depth and forms an ulcer which usually becomes covered with a layer of epithelium and gradually fills up, the cornea regaining more or less of its transparency.
COURSE.-It is usually acute, though it may be very chronic, as there is a great tendency to relapses. Just as the symptoms of irritation and vascularity are subsiding, the phlyctenule disappearing and the disease seems to be almost cured, all the acute symptoms return, a fresh crop of pustules make their appearance and a severe relapse takes place. This may occur again and again and the affection assume a chronic character.
CAUSES.-It is most frequently found in children and young persons of a weakly, scrofulous constitution and those of a nervous, excitable temperament. It is often found after the exanthematous diseases or in eczema of the face, from confinement in close, dusty rooms, after exposure to cold or moisture.
PROGNOSIS.-Depends upon the course and extent of the disease. Each attack in itself should be promptly treated, when it will usually heat in a short time, as it yields readily to treatment. When due to scrofula there will probably be relapses and more or less loss of sight will occur from macula, if the location be central.
TREATMENT.-As the treatment of this disease is precisely the same as that for conjunctivitis phlyctenularis, what is there said of treatment applies as well to keratitis phlyctenularis and avoids unnecessary repetition. (See Conjunctivitis Phlyctenularis, page 213.)
Keratitis Fascicularis.-This disease is very similar to and may occur with phlyctenular keratitis. It consists of a vascularized infiltration in which there is a narrow band of vessels running parallel to each other and extending into the cornea. At the end of this fasciculus of vessels there is a more or less crescentic-shaped infiltration, which is often ulcerated. There is usually but one such infiltration, although several may occur at the same time. There are the usual symptoms of pericorneal injection, photophobia and lachrymation. The affection is mostly found in scrofulous children and its treatment is the same as that for phlyctenular keratitis. The yellow oxide of mercury ointment is often of special value in this form of keratitis.
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.