The human eye
What are the main parts
of the human eye?
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Ciliary muscle
Cornea
Iris
Lens
Optic nerve
Pupil
Retina
Sclera
Vitreous humor
Aqueous humor
Correction
Sclera ; iris ; pupil ; cornea
• Sclera
• The sclera is the white of the eye. "Don't shoot until you
see their scleras."
• Cornea
• The cornea is the clear bulging surface in front of the eye. It
is the main refractive surface of the eye.
• Iris/Pupil
• Iris is heavily pigmented
• Pupil is the hole through which light passes
• Pupil diameter ranges from about 3-7 mm
• Eye color (brown, green, blue, etc.) depends on the amount
and distribution of the pigment melanin
Human eye color charts
Lens ; ciliary muscles
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Transparent body enclosed in an elastic capsule
Made up of proteins and water
Gradient refractive index (1.38 - 1.40)
Young person can change shape of the lens
thanks to ciliary muscles
• Contraction of muscles causes lens to bulge
• At roughly age 50, the lens can no longer change
shape : presbyopia
• Becomes more yellow with age: cataracts
Retina
• The light has to pass through many layers of cells
before finally reaching the photoreceptors. The
photoreceptors are where the light is absorbed and
transformed into the electrochemical signals used by
the nervous system. This change is called transduction.
There are two types of receptors: the rods (rodshaped) and the cones (cone-shaped).
• The rods enable us to see black and white; the cones
enable us to see the colors.
• Three types of cones exist:
• cones that absorb long-wavelength light (red)
• cones that absorb middle-wavelength light (green)
• cones that absorb short-wavelength light (blue)
Rods and cones
Two kinds of lenses
Experiments
Method to determine the focal length
Defects of vision
Optical illusions