Chapter 2Chapter 2The Human Eye

Physics ReviewPhysics ReviewLight

◦ 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

The HeadThe HeadEye placement:

◦ Lateral vs. FrontalSkull: OrbitEye Movement

◦ 6 extra-ocular muscles: Conjugate: move

together Vergence: move

opposite

Eyelids:◦ Protection and

moisture◦ Blinking and Distance

Tears

Eye FunctionEye FunctionImage: 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

Eye StructureEye StructureThree layers:

◦Protecting: Fibrous Tunic◦Nourishing: Vascular Tunic◦Detecting: Retina

Fibrous TunicFibrous TunicSclera – “white” of eye, dense

material, gives eye it’s shapeCornea – transparent “bulge”,

allows light into eye

Out of FocusOut of FocusCondition Common

nameEye Shape

Location of focus

Lens needed

Myopic Nearsighted

Too Long In front of retina

Concave

Hyperopic Farsighted Too Short Behind retina

Convex

Emmetropic

Normal Normal On fovea None

Problems with LensProblems with LensPresbyopia:

◦loss of sight with age

Astigmatism:◦Distortion of cornea

Vascular TunicVascular TunicChoroid

◦Pigment epithelium◦Contains blood vessels

and capillaries◦Reduces light scatter

and disposes of wasteAnterior Chamber

◦Manufactures aqueous humor

◦Contains: Iris/Pupil Lens

RetinaRetinaContains

photoreceptors

Landmarks:◦ Macula (1.5mm

diameter): focus of eye, contains fovea

◦ Optic Disk: “blind spot”

PhotoreceptorsPhotoreceptorsOrder of stimulation:

PhotopigmentsPhotopigmentsTwo components

◦Opsin: large protein, 3 types◦Retinal: from vitamin A

Phototransduction

Wavelength SensitivitiesWavelength Sensitivities

Cell Most Sensitive Wavelength

Relative “color”

Rods 500 nm Bluish-green

Cones440 nm Violet

530 nm Green

560 nm Yellow