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The Human Visual System The Human Visual System The Eye

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Page 1: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

The Human Visual SystemThe Human Visual SystemThe Eye

Page 2: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Anatomy of the Human EyeAnatomy of the Human Eye

Cornea

Pupil

Iris Sclera

Retina

Optic Nerve

Lens

Page 3: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Human Visual SystemHuman Visual System

RefractionCornea & Lens

Light ControlIris

(& Pupil)

Light Detection

Retina

ProcessingBrain

Page 4: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Image FormationImage Formation

The image projected onto the retina is upside down.

Object Image

Page 5: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

CorneaCornea The outer wall of the eye is formed by the hard, white sclera.

The cornea is the clear portion of the sclera.

Most of the refraction takes place at the cornea.Why?

Sclera

Cornea

Page 6: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Iris and PupilIris and Pupil The colored iris controls the size of the opening (pupil) where the light enters.

The iris controls the amount of light, like the aperture of a camera.

Iris

Pupil

Page 7: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Iris openDilated pupil

Iris closedConstricted pupil

Page 8: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

LensLens The lens is transparent. The lens can change

shape. This is what allows you to

focus on objects at different distances.

For close objects, the lens becomes thicker.

For far objects, the lens becomes thinner.

Lens

Ciliary muscle

TransparentFibers

Cross section of the eye lens

Page 9: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

AccommodationAccommodation The lens is attached to

the ciliary muscle. When the muscles

contract, the lens becomes thicker.

When the muscles relax, it becomes thinner.

The process by which the lens changes shape to focus is called accommodation.

Relaxed muscleTaut ligamentsDistant object

Near objectContracted muscleSlack ligaments

Page 10: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Muscle relaxes

Distant object

Lens gets thinner

Object is in focus

Page 11: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Muscle contracts

Near object

Lens gets thicker

Object is in focus

Page 12: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Aqueous Humor and Vitreous HumorAqueous Humor and Vitreous Humor

Transparent gelatinous liquid filling the eye.

Provides nutrients to the cornea and eye lens.

Also helps maintain the eyeball shape with its pressure.

Vitreous Humor

Aqueous Humor

Page 13: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

RetinaRetina The Retina is the light detector for the eye.

Two types of receptors in the retina: rods for low light level cones for color.

Signals from the receptors leave through the optic nerve to the brain.

Retina

Optic Nerve

Page 14: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Blind SpotBlind Spot The retina has a hole

in it where the optic nerves exit the eye.

This is because the nerves run in front of the retina.

Our brain fills in the blank spot with surrounding colour, so it’s hard to notice

“Hole” in retina

Photo receptors

Optic Nerve

Light

Page 15: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Rods and ConesRods and Cones

Only black, grey, white Only in low light levels.

Rod cell Cone cell

Three types of cones in order to detect colour

Requires a lot of light

Page 16: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Mach BandsMach Bands

Actual brightness

Perceived by you

Page 17: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Eye Defects*Eye Defects*

Image focuses on the retina for a normal eye.

Distant objects look blurry for a myopic (near sighted) eye.

Near objects look blurry for a hyperopic (far sighted) eye.

Normal

Myopic

Hyperopic

Object at infinity

Page 18: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Myopia – Near-sightednessMyopia – Near-sightedness Distant objects look

blurry because the eye cannot relax any farther so that the image is focused before the retina.

Near object in focus without accommodation.

Corrected with a diverging lens.

Myopic eye relaxedBlurry

Myopia corrected with a negative lens

Far object

Near objectMyopic eye relaxedIn focus

Far object

Page 19: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Hyperopia – Far-sightednessHyperopia – Far-sightedness Near objects look

blurry because the eye cannot accommodate enough for near objects.

Far object in focus. Corrected with a

converging lens.

Hyperopic eye Partially accommodatedIn focus

Hyperopia corrected with a positive lens

Far object

Hyperopic eye Fully accommodatedBlurry

Near object

Near object

Page 20: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Contact LensContact Lens

Contact lens is an alternative to corrective lenses.

Changes the curvature of the cornea by adhering to the surface with some fluid.

CorneaContact lens

Fluid

Page 21: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Presbyopia - “Old eye”Presbyopia - “Old eye”

Lens hardens with age. Eye cannot adequately

accommodate near objects.

Bifocals (lens with two focal lengths) contains a concave lens for distance (if needed) and a convex lens for near objects.

Near objects magnified

Far objects

Concave for distance correction (if needed)

Convex for near objectcorrection

Page 22: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

AstigmatismAstigmatism

The cornea is not spherical; Focal length different from one plane to a perpendicular plane.

F’ horizontal

F’ Vertical

Object

Image at F’ Vertical

Image at F’ Horizontal

Cornea

Direction of blur

Page 23: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

AstigmatismAstigmatism

Correction of astigmatism is done through the use of a cylindrical lens.

Cylindrical lens converge rays in one plane but not the perpendicular plane.

Cylindrical lens

Rays in the vertical plane are undeviated

Rays in the horizontal plane are focused

Page 24: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Common Eye Diseases*Common Eye Diseases*

Cataract - Clouding of the lens. Symptom: Loss of vision Cure: Lens replacement

Glaucoma - Pressure buildup in the eye, damaging the retina. Symptom: Loss of vision first in the periphery. Cure: Surgery to drain fluid from the eye.

Loss of vision is usually permanent

Page 25: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Common Eye Diseases (cont’d)*Common Eye Diseases (cont’d)*

Detached retina - portion of the retina detaches from the back of the eye. Symptom: Perception of flashes,

Loss of vision Cure: Laser surgery to reattach

retina Pink eye - Infection of the surface of

the eye. Symptom: Irritation Cure: Antibiotics

Ow!

Page 26: The Human Visual System The Eye. Anatomy of the Human Eye Cornea Pupil Iris Sclera Retina Optic Nerve Lens

Your eye careYour eye care

Go see a doctor if you think there is something wrong with your eye-

Early detection is essential to keeping damage low and preventing permanent loss of your vision.