. Physiological optics : being an essay contributed to the American encyclopedia of ophthalmology . Eig. 76.—Speckled Appearance of the Entoptic Field Produced by Eubbing the Cornea. (After George Bull.) have an apparent motion after an excursion of the eyelid; they aredue to small specks on the anterior surface of the cornea and actuallymove in a direction contrary to their apparent motion. (4) On closing and then opening the eyelids, after looking at adistant luminous point, long striae running vertically are often are produced by the layer of tears in the conjunctival sac and 158
. Physiological optics : being an essay contributed to the American encyclopedia of ophthalmology . Eig. 76.—Speckled Appearance of the Entoptic Field Produced by Eubbing the Cornea. (After George Bull.) have an apparent motion after an excursion of the eyelid; they aredue to small specks on the anterior surface of the cornea and actuallymove in a direction contrary to their apparent motion. (4) On closing and then opening the eyelids, after looking at adistant luminous point, long striae running vertically are often are produced by the layer of tears in the conjunctival sac and 158 PHYSIOLOGICAL OPTICS which assume near the borders of the eyelids a prismatic form withan outer concave and inner convex surface. Because of this shape ofthe tear-prism we have a prism of varying power and hence striserather than doubled images are produced. (5) A rubbing of an eye causes the luminous spot to become. Tig. 77.—Star Figure of the Crystalline Lens. (After Helmholtz.) speckled or mottled, due to the slight irregularities of the cornea orthe irregular laying down of tear fluid. This soon disappears. (after G. Bull) shows the speckled appearance of the entoptic fieldproduced by rubbing the cornea. (6) The star figure of the crystalline lens can frequently be seen.
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