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1

The eye

•  Basic anatomy •  Optics and retinal image formation:

pinhole camera, cornea, lens, myopia/hyperopia, presbyopia, blind spot, visual angle

•  Types of eye movements

pupil

cornea lens

fovea

optic nerve retina

optic nerve fibers

photoreceptors

The eye

Cross-section of the vertebrate eye! Cross-Section of the Eye

Cornea Lens

Retina

Optic disk

Glaucoma Secondary glaucoma

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2

Detached retina

Schiotz tonometer

Ouch! Non-contact tonometer

Measures the time from the generation of the air puff until the cornea is flattened. It takes less time for the puff to flatten a soft eye than it does a hard eye.

Mike May

S.B.

Some properties of light •  Light bounces off of surfaces (reflection)

•  Light bends when the index of refraction changes

(refraction)

•  The amount of refraction depends on wavelength (the prism’s rainbow, dispersion)

•  Light bends when passing by an edge or through a small aperture (diffraction)

air water

or glass

air water

or glass

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3

Image formation Retinal projection depends on size and distance

Visual angle Visual angle

Pinhole optics Pinhole size

Aperture

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4

Normal eye

Focused for near (e.g. 70 D)

Focused for far (e.g. 60 D)

Object in world far

away

Object in world near

Good

Good

Myopic (nearsighted) eye

Focused for near (e.g. 70 D)

Focused for far (e.g. 60 D)

Object in world far

away

Object in world near

Good

Hyperopic (farsighted) eye (shown here with hyperopia caused by shortened eyeball)

Focused for near (e.g. 70 D)

Focused for far (e.g. 60 D)

Object in world far

away

Object in world near

Good

The Eye’s Optics •  Gathering and focusing light vs. image formation •  Focal power is measured in diopters: Focal power is 1/focal

length (diopters are in units of 1/m). •  The eye has a focusing power of 60+ Diopters (D)

–  60 D when focused far, more when focused near –  What is the focal length of the eye? 1/x = 60 D... –  Cornea: 43 D, Lens: 17+ D –  Young children can accommodate 20 D; teenagers 10 D, 60-year-

olds typically only 0.5 D at best. –  Bionic lenses? –  Myopia, hyperopia, presbyopia, and emmetropia

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5

Right eye in bony orbit Eye movements

•  Why torsion? (Listing’s Law) •  Basic types of eye movements

– Saccades – Smooth pursuit – Nystagmus (including optokinetic) – Vestibulo-ocular reflex – Vergence – Tremor, microsaccades