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ticularly in the skin of the negro), in the epithelial cells of the external layer of the retina (then called fuscin), in the outer layer of the choroid, and elsewhere. It is supposed to be derived from the decomposition of hemoglobin.

rs (Anat.), the sustentacular or connective-tissue fibers which form the framework of the retina.

A substance, present in the protoplasm of the retinal epithelium cells, and resembling, if not identical with, the substance (myelin) forming the medullary sheaths of nerve fibers.

he eye in which the rays from distant object are brought to a focus before they reach the retina, and hence form an indistinct image; while the rays from very near objects are normally converged so as to produce a distinct image. It is corrected by the use of a concave lens.

An instrument for viewing the interior of the eye, particularly the retina. Light is thrown into the eye by a mirror (usually concave) and the interior is then examined with or without the aid of a lens. -- Oph*thal`mo*scop"ic, a.

lar; as, the optic nerves (the first pair of cranial nerves) which are distributed to the retina. See Illust. of Brain, and Eye.

An image of external objects fixed on the retina by the photochemical action of light on the visual purple. See Optography.

The production of an optogram on the retina by the photochemical action of light on the visual purple; the fixation of an image in the eye. The object so photographed shows white on a purple or red background. See Visual purple, under Visual.

ping, etc., in consequence of the persistence of the successive visual impressions of the retina. It is often arranged so that the figures may be projected upon a screen.

A luminous impression produced through excitation of the retina by some cause other than the impingement upon it of rays of light, as by pressure upon the eyeball when the lids are closed. Cf. After- image.

on of light, or produced by it; as, the photochemical changes of the visual purple of the retina.

A more or less continued impression or image on the retina. H. Spencer.

That part of the eye of an invertebrate which corresponds in function with the retina of a vertebrate.

Inflammation of the retina.

The study of the retina of the eye by means of the ophthalmoscope.

The red pigment contained in the inner segments of the cones of the retina in animals. See Chromophane. W. KÜhne.

. -- Rods and cones (Anat.), the elongated cells or elements of the sensory layer of the retina, some of which are cylindrical, others somewhat conical.

device for determining the refractive state of the eye by observing the movements of the retinal lights and shadows. -- Ski*as"co*py (#), Ski*as"co*py (#), n.

iant with immense, but measurable, velocities, and producing different impressions on the retina according to their amplitude and frequency, the sensation of brightness depending on the former, that of color on the latter. The undulations are supposed to take place, not in the direction of propagation, as in the air wa…

l objects are appreciated as a result of the stimulating action of light on the sensitive retina, an expansion of the optic nerve.