Opacities visible with the ophthalmoscope usually come from effusion of blood into the vitreous, or inflammation of the retina, choroid, or ciliary body. Blood thrown into the vitreous will usually leave some permanent turbidity. In choroiditis or retinitis the ophthalmoscope may reveal the changes in these structures. A turbidity appearing in the anterior portion of the vitreous, without any apparent cause, is probably due to cyclitis which cannot be seen with the ophthalmoscope, but may cause special tenderness around the sclero-corneal zone. It is common in recurrent ophthalmia of the horse and in irido-choroiditis in animals generally, and may be a distinct feature of glaucoma. The general reflection of the pupil is copperas green, but gray or white points, lines, bars or patches may often be recognized. These being back of the lens and axis of the eye, move in the opposite direction from the line of vision, thus if the eye looks upward they descend, if it looks downward they ascend, if it turns to the right, they turn to the left and vice versa. Tested by a burning candle the three reflections remain clear and distinct unless lens or cornea are affected.
Not infrequently the vitreous is found abnormally fluid, and among its solid particles in affected horses have been found crystals of cholesterin (Jacobi) and tyrosin (Möller). In the illuminated vitreous such crystals may be seen to reflect the light like a shower of sparks (synchysis scintillans). Opacity of the vitreous has been seen in cases of amaurosis in horses (Hertwig) and glaucoma in lambs (Prinz).
Treatment is rarely satisfactory, though in some recent cases, and in the absence of any other irremovable lesion, reabsorption of a slight exudate may take place, in connection with the use of mild saline laxatives and diuretics.
RETINITIS.
With choroiditis and cyclitis, albuminuria, nephritis, mellituria, leukæmia, petechial fever, contagious pneumonia. Photophobia, contracted pupil, redness around optic disc, enlarged retinal vessels, white and gray spots and radiating lines, exudates, clots, fatty degeneration. Treatment: correct primary disease.
Retinitis is usually an accompaniment of choroiditis and cyclitis, but it also occurs as a complication in a number of constitutional maladies, such as albuminuria, nephritis, mellituria, leukæmia, petechial fever, contagious pneumonia, etc. Fröhner records a case in a leukæmic horse, Peters in one suffering from petechial fever, Schindelka in cases of contagious pneumonia in the horse, and Eversbusch in recurrent ophthalmia of the horse, and under other conditions in dogs.
The attack is accompanied at the outset with much photophobia and contraction of the pupil. When this is dilated and the fundus of the eye examined with the ophthalmoscope, the retina is seen to be reddened for some distance around the optic disc and the blood-vessels are materially enlarged. Later, white or gray spots and lines are seen in and around the disc, tending to assume a radiating direction, and the retina at large, on careful examination may have a distinctly striped appearance. Brownish, reddish or light colored exudates and hæmorrhages may be made out in certain cases between retina and hyaloid, or between the retina and choroid. Fatty degeneration of the fibrous tissue is common.
Treatment must be first that for the primary disease of which the retinitis is a complication, and the result will depend on how amenable that affection is to therapeutic measures. In advanced albuminuria or mellituria, the retinitis, which is usually double, is hopeless, while in contagious pneumonia, petechial fever, leukæmia and other less fatal affections, retinitis in its initial stages may recover. In cases of advanced disease with serious structural changes in the retina, recovery cannot be looked for.
DETACHMENT OF THE RETINA.
This may occur in any case of retinitis or choroiditis. It is especially common in recurrent ophthalmia in horses. It may also occur through the dragging by contracting inflammatory products in organization. Spontaneous recoveries have taken place through reabsorption, and attempts have been made by the injection of iodide lotion to hasten this, or more safely by rest and diaphoresis. Puncture and aspiration have also been tried with most varied results. As a rule in the lower animals the treatment of the inflammation, with rest, a pressure bandage, and pilocarpin will be indicated.