physiology of vision including photoreceptors , day anad night vision, color blindness

The above mentioned powerpoint presentation highlights physiology of vision alongwith color vision

1. Image Formation Dr. Asma , Deptt . Of Physiology, HCMD

2. cornea and lens focus an image of distant objects on retina “film ” . contraction of ciliary muscles changes s hape of lens to bring objects to focus. Adjustment of pupillary diameter helps maintain proper light exposure to retina.

3. accommodation of the lens constriction of the pupil controlled by smooth muscle fibers of ciliary muscle and iris.

4. REFRACTION ‘The bending of light as it passes at an oblique angle from one medium (such as air) to another (such as water).’

5. Refract ion 3/4 of the focusing occurs on the cornea L ens is responsible for fine- tuning of image C onvex surface of the lens causes light waves to converge (come to a point ) . C oncave surface of lens causes light waves to diverge (fan out ) . N ormal eye shape causes light waves to sharply focus s on retina .

6. Light Refraction light waves of distant objects travel at almost parallel angles - focused on retina by cornea and flatter lens light waves of nearer objects reach eye in a more divergent line - the closer the object, the more divergent the lines

7. Visual Pathway B egins in photoreceptors of retina - stimulated by image focused on retina R eceptor potentials travel via optic nerve to lateral geniculate nucleus in thalamus then on to visual cortex on occipital lobe . P rocessing of visual information along entire pathway .

8. RO DS P re d ominant type o f photoreceptors , found in all areas of retina except fovea centralis . E xtremely sensitive to light . I n dim light stimulated. D o not distinguish color . A ll night images black + whi te , unsharp .

9. Outer segment of Cones T ransduction of light. Outer segment of Lamellar membrane holds pigment- containing saccules . Many flattened saccules (lamellae) arranged parallel to surface of retina  carries photosensitive pigment => Rhodopsin .

10. Inner Segment of Cones Inner segment contains : many mitochondria cell nucleus Large synaptic base which most likely contains neurotransmitter => Glutamate

11. blue- green green- sensitive red- sensitive

12. Color Blindness Absence or deficiency of one of the three photopigments inherited condition ( Color genes located on X chromosomes, dominant trait) most common type is red- green X- linked