BIO 208 Lecture Notes - Lecture 13: Macula Of Retina, Amacrine Cell, Ciliary Muscle
Document Summary
Focusing and vision: when an object is less than 20 feet from the eye, the image falling on retina is no longer in focus, three events must occur to bring the image into focus, accommodation by the lens. Contraction of the ciliary muscles causes the lens to become mosre spherical. Change in the lens shape enables the eye to focus on objects that are less than 20 feet away: constriction of the pupil. Greater proportion of the light passes through center of lens, better focus- prevents divergent rays from entering and creating blurriness: convergence of the eyes. Medial rotation of the eyes so that each eye is directed towards the object (move nger towards eye= going cross-eyed . Problems with accommodation: myopia: nearsighted , eyeball to deep, lens unable to atten enough, hyperopia: farsighted , eyeball too shallow, lens unable to accommodate, presbyopia, age-related hyperopia due to loss of elasticity in lens (cannot form a round spherical lens)
