Ishara Mills-Henry, Ph.D.MIT

Human Eye

Cows versus HumansWhat can they see and what can we see?

External Tissue of Eye

Cow Eye

Human Eye Orbit

Eye movements

http://www.michaelbach.de/ot/mot_eyeJitter/index.html from Pinna B & Spillmann L (2002) A new illusion of floating motion in depth. Perception 31:1501–1502.

Cow Eye

Cornea – Refractive Errors

Pictures taken from www.essilor.com.au

Myopia – NearsightednessHyperopia - Farsightedness

Pictures taken from www.essilor.com.au

Corrective LensesMyopia

concave lens will correct the problem by focusing the light farther onto the surface of the retina.

Hyperopia 

a convex lens will refract light rays allowing them to focus directly onto the retina.

Lasik

Iris and Pupil

Pupil changes size to adjust for light levels (like an aperture)

Let’s take a peak inside…

Lens

AccommodationClose one eye and stare at a point about 20 feet

away. Keep focusing on the point and raise one of your

fingers into your line of sight just below the point.

How does your finger look?

Now, change focus: look at the tip of your finger instead of the point 20 feet away.

How does the distant image look?

AccommodationFar Away Objects – The zonule fibers provide tension to the lens giving it an elongated shape.

Close Objects – Ciliary muscles contractRelaxes the tension of the lens leading to a rounder shape changing the focal length of the eye. This brings objects that are closer to the eye into focus.

Presbyopia

• Limited lens accommodation

Cataract

www.nih.nei.gov

Retina

Color Vision

Optic NerveWhere’s my blind spot?

Why is it so hard to find?

Where’s my blind spot?

Why is it so hard to find?

Right Eye

Left Eye

Glaucoma

Bloodshot eyesInflammation of blood vesselson sclera (white of eye)

CausesConjunctivitis (pink eye)Dry eyeEye strainAlcohol induced

Why more men than women?1 in 12 people have some sort of color

deficiency. About 8% of men and 0.4% of women in the US.

Some types of color vision deficiency are sex–linked diseases