1. EYE

2. CONJUNCTIVA • Transparent mucous membrane lining the eyelids and covering anterior surface of eyeball except cornea • Richly innervated • Vascular

3. Lacrimal Apparatus • Tears with bactericidal enzyme flow across the eyeball, wash away foreign particles, and help with diffusion of O2 & CO2.

4. Extrinsic Eyes Muscles trochlea • Innervated by cranial nerves III, IV and VI • 4 rectus muscles move eye up, down, left & right • superior & inferior oblique are complicated

5. The Tunics of the Eyeball • Fibrous layer (tunica fibrosa) = sclera and cornea • Vascular layer (tunica vasculosa) = choroid, ciliary body & iris • Internal layer (tunica interna) = retina and optic nerve

6. OPTICAL COMPONENTS • Transparent structures that refract (bend) light rays to focus them on the retina 1. Cornea - covers anterior surface of eyeball 2. Aqueous humor - clear serous fluid located between lens and cornea 3. Lens - suspended by ring of suspensory ligaments 4. Vitreous humor - jelly-like located between the lens and retina

7. NEURAL COMPONENTS 1. Retina - out growth of diencephalon - pressed against rear of eyeball by vitreous body 2. Optic nerve - attached to retina at the optic disc

8. IMAGE FORMATION 1.Light passes from an object through the lens 2. A tiny inverted image forms on the retina • Pupillary constrictor (smooth muscle) in iris narrows the pupil in bright light • Pupillary dilator (radial & myoepithelial) widens the pupil in dim light

9. Refraction • Bending of light rays occurs when light passes through substance with different refractive index at any angle other than 90 degrees • refractive index of air is arbitrarily set to n = 1 • refractive index of cornea is n = 1.38 • refractive index of lens is n = 1.40 • Cornea refracts light more than lens does • lens fine-tunes the image as shift focus between near and distant objects

10. ACCOMMODATION • Allows the lens to focus on close objects 1. Contraction of ciliary muscle relaxes suspensory ligaments 2. Lens becomes more convex in shape 3. Light is refracted more strongly & focused onto retina

11. Emmetropia (Distant Vision) & Accommodation (Near Vision)

12. Accommodation of Lens

13. EYE DEFECTS • Hyperopia - farsightedness - due to short eyeball - correct with convex lenses • Myopia - nearsightedness due to long eyeball - correct with concave lenses

14. Effects of Corrective Lenses

15. Retinal Cells • Posterior layer of retina is pigmented epithelium - absorbs excess light & prevents reflections • Photoreceptors are anterior to epithelium 1. Rod cells - allow night vision - outer segment has a stack of membranous discs containing rhodopsin (pigment) 2.Cone cells - allow color vision in bright light - outer segment tapers to a point

16. Non-receptor Retinal Cells • Bipolar cells (1st order neurons) • synapse on ganglion cells • moderate convergence occurs • Ganglion cells (2nd order neurons) • axons form optic nerve • great convergence occurs • Horizontal & amacrine cells form connections between other cells

17. VISUAL PIGMENTS 1. Rhodopsin (visual purple) - in rod cells - consists of opsin (protein) & retinal (vitamin A derivative) 2. Photopsin (iodopsin) - in cones - 3 kinds of cones absorb different wavelengths of light to produce color vision

18. PHOTOCHEMICAL REACTION IN RODS • Rhodopsin absorbs light & converts from a bent shape (cis-retinal) to a straight (trans-retinal) form that dissociates from opsin (bleaching) • 50% of rhodopsin is regenerated 5 minutes after bleaching occurs

19. Rods and Impulse Transmission

20. Color Vision • Cones permit color vision • Cones are named for absorption peaks of photopsins • blue cones peak sensitivity at 420 nm • green cones peak at 531 nm • red cones peak at 558 nm (orange-yellow) • Perception of color is based on mixture of nerve signals • Color blindness is hereditary lack of one photopsin • Red-green color blindness (sex-linked recessive trait found in 8% of males) occurs if an individual lacks either red or green cones

21. Test for Red-Green Color Blindness

22. Rods vs. Cones RODS CONES