The American encyclopedia and dictionary of ophthalmology Edited by Casey A Wood, assisted by a large staff of collaborators . the relation sin i/ sinr = a constant (the index of refraction), this relation being known asSnells Law, from its discoverer, Willibrod Snellius.—Angle-true, seeOrthoscopic. Critical angle, the limiting angle of incidence which,within a medium more dense than air, separates the totally reflectedrays from those which, at least partially, escape into air. (C. F. P.)Angle alpha. This angle, generally written angle a measuring from 5°to 7°, is formed by the junction of the
The American encyclopedia and dictionary of ophthalmology Edited by Casey A Wood, assisted by a large staff of collaborators . the relation sin i/ sinr = a constant (the index of refraction), this relation being known asSnells Law, from its discoverer, Willibrod Snellius.—Angle-true, seeOrthoscopic. Critical angle, the limiting angle of incidence which,within a medium more dense than air, separates the totally reflectedrays from those which, at least partially, escape into air. (C. F. P.)Angle alpha. This angle, generally written angle a measuring from 5°to 7°, is formed by the junction of the visual axis and the opticaxis. The visual axis, or visual line, is the ray which passes throughthe first nodal point of the eye to the fovea after having been re-fracted so as to pass through the second nodal point. The locationof this axis is not constant, being dependent upon the varying fixing ANGLE, BI-ORBITAL 471 point of the fovea. Nor is the optic axis a constant, for this is theline passing through at least three of the four centers of curvatureof the cornea and lens. Congenital anomalies of these structures. L Wm LIVEAS- Of Tic hxii o^ - ANQie Al?HA • •• ? f>o%r • - •• •• ?. PotT .. Angle Alpha. displace the linear position of the points; consequently this decenter-ing must be neglected.— (H. G.) Angle, Bi-orbital, The angle subtended by the axes of the orbits. Angle, Co-orbital. In craniometry, the angle made by the anatomicalplane, where it crosses the bi-orbital plane. Angle epsilon. Landolts name for the angle included between themacular axis and the papillary axis. It is usually greater in hyper-opes than in myopes. Angle gamma. This term, usually written, angle y, is merely anothername for the angle alpha (q. v.). It is also known as theangle beta, (6), according to the individual authors definition. SeePhysiological optics. Angle, Great, of the eye. The inner canthus, or angle formed by thejunction of the upper and lower lids. Angle kap
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