21.Light the only stimulus capable of stimulating the photoreceptors of : 1417044
21.Light is the only stimulus capable of stimulating the photoreceptors of the eye.
22.Parasympathetic neurons stimulate the circular muscle of the iris to contract in response to dim light.
23.Sympathetic stimulation of the iris causes contraction of the radial muscle and thus produces pupil dilation.
24.The sclera is the most external layer of the eye and the choroid is the most internal layer of the eye.
25.A convex lens converges light rays or brings them closer together.
26.The greater the curvature of a lens, the greater its ability to refract light rays.
27.The fovea is the point on the retina where the optic nerve leaves.
28.The curvature of the lens must be adjusted to enable the eye to focus both near and far sources on the retina.
29.Light rays passing through a concave lens undergo convergence.
30.The term cataract refers to the condition in which the lens becomes stiff and loses its elasticity.