Download Human Vision: Electrophysiology and Psychophysics

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Transcript
Human Vision:
Electrophysiology
and
Psychophysics
The Lens
Several biological visual systems
include one or several lenses
What is a lens?
Convex lens
Concave lens
This takes place by refraction
What is refraction?
The refractive index of a
transparent substance is
the ratio of the velocity
of light in air to that in
the substance
Converging lens
1/f = 1/a + 1/b
a
b
The Diopter
Refractive power = 1 m/ focal length
The eye
Eye is equivalent to a camera with a variable aperture
system. The retina is the film and the pupil the variable
aperture.
The eye is capable of vision in
conditions of light that vary greatly in
intensity
Accomodation
Distant vision
Close vision
Presbyopia – Condition in old age where the lens
loses its capacity to change shape.
Refractive indices of the eye
Total refractive power of the eye is 59 diopters
Vitreous humour
Lens
Aqeous humour
Cornea
Air
1.34
1.4
1.33
1.38
1.00
Image inversion
Common problems in vision
Emmertropia
Hypermetropia
Myopia