1. Chapter 2 The Human Eye

2. Physics Review Light ◦ Electromagnetic radiation ◦ Wavelength determines quality  Measured in nanometers ◦ Why light?  Reliable: Travels very fast and straight  Prevalent: Lots of it  Informative: Reflected/Absorbed by surface molecules

3. The Head Eye placement: ◦ Lateral vs. Frontal Skull: Orbit Eye Movement ◦ 6 extra-ocular muscles:  Conjugate: move together  Vergence: move opposite Eyelids: ◦ Protection and moisture ◦ Blinking and Distance Tears

4. Eye Function Image: light distribution that preserves the spatial ordering of locations in space Image formation – reversing light divergence ◦ Optical power of:  1) cornea: 2/3rds of eye’s optical power  2) lens: flexing called accommodation

5. Eye Structure Three layers: ◦ Protecting: Fibrous Tunic ◦ Nourishing: Vascular Tunic ◦ Detecting: Retina

6. Fibrous Tunic Sclera – “white” of eye, dense material, gives eye it’s shape Cornea – transparent “bulge”, allows light into eye

7. Out of Focus ConditionCommon name Eye ShapeLocation of focus Lens needed MyopicNearsightedToo LongIn front of retina Concave HyperopicFarsightedToo ShortBehind retinaConvex EmmetropicNormal On foveaNone

8. Problems with Lens Presbyopia: ◦ loss of sight with age Astigmatism: ◦ Distortion of cornea

9. Vascular Tunic Choroid ◦ Pigment epithelium ◦ Contains blood vessels and capillaries ◦ Reduces light scatter and disposes of waste Anterior Chamber ◦ Manufactures aqueous humor ◦ Contains:  Iris/Pupil  Lens

10. Retina Contains photoreceptors Landmarks: ◦ Macula (1.5mm diameter): focus of eye, contains fovea ◦ Optic Disk: “blind spot”

11. Photoreceptors Order of stimulation: PhotoreceptorsBipolar CellsAmacrine CellsHorizontal CellsRetinal Ganglion Cells

12. Photopigments Two components ◦ Opsin: large protein, 3 types ◦ Retinal: from vitamin A Phototransduction Light Isomerize opsin and retinal Reduction of Current Reduction of Transmitter (Glutamate) Release

13. Wavelength Sensitivities CellMost Sensitive Wavelength Relative “color” Rods500 nmBluish-green Cones 440 nmViolet 530 nmGreen 560 nmYellow