The Visual System 1 - the Eye and Retina

Question 1

Recall the major anatomical structures of the eye.

Answer 1

image

Question 2

Describe the mechanisms that focus a sharp image on the retina.

Answer 2

For image formation, light focuses on the retina (ideally, fovea)

80% of refraction occurs by cornea, 20% by lens

Lens accommodation
-Lens flattens for distant objects, relaxed ciliary muscle
-Lens rounds for closer objects to increase refractive power, contracted ciliary muscle

Question 3

Explain the functional significance of having different types of photoreceptors

Answer 3

Photoreceptors contain light sensitive photopigments that absorb light

Duplicity theory - cant have high sensitivity and high resolution in single receptor

Rod photoreceptors
-More discs
-Higher photopigment concentration
-More sensitive to light
-Enables vision in low light
-Low visual acuity, low resolution

Cone receptors
-Fewer discs
-Used during daylight conditions
-Colour visions
-High visual acuity, high resolution
-Lower sensitivity to light
-Contains ⅓ different types of photopigments

Fovea has no rods, most of the cones, low convergence of retinal ganglion cells

Central retinal - low convergence, low sensitivity, high resolution

Peripheral retina - high convergence, high sensitivity, low resolution