Eye

Sclera

• outermost, protective layer (coat)

• thick white connective tissue

• white of the eye

Cornea

transparent part of the sclera in which light enters

Choroid

• Vascular tunic - nourishes the vitreous humor

• Highly pigmented - prevents light scattering

• Choroid is modified anteriorly to form the ciliary body

• Iris and Pupil

ciliary body

smooth muscles which attaches to the lens and iris

Iris

circular pigmented structure which helps regulate the amount of light entering the eye

Pupil

the rounded opening of the iris, light passes through it

Retina

• innermost - sensory tunic

• extends to the ciliary body

• contains millions of receptors (photoreceptors): rods and cones

• Rods and cones are distributed all over the retina except at the optic disc (- blind spot)

• Lateral to each blind spot is the fovea centralis

Rods

function in low light, at night

Cones

function in bright light (blue, green, red)

Fovea Centralis

area of greatest visual acuity (only cones)

Rods vs Cones

Cones:

• cone shaped

• clustered around the fovea centralis

• less abundant

• daylight vision

• color vision RBG

Rods:

• rod shaped

• located on the retina’s periphery

• more abundant

• low light vision

• gray scale

Aqueous vs Vitreous Humors

Aqueous:

• Anterior - in front of lens

• liquidy

• maintains structure of the eye

• nourishes

• replenishes - drains into the canal of Schlemm

Vitreous:

• Posterior - in back of lens

• gel-like

• maintains structure of the eye

• does not nourish

• does not replenish

Pathway of Light

1. cornea

2. Aqueous Humor

3. Pupil

4. Lens

5. Vitreous Humor

6. Cones/rods

7. Optic Disk

8. Optic Nerve

9. Optic Chiasma

10. Thalamus

11. Occipital Lobe

Disorders

• cataracts: lens (cloudy/hardening) = age

• glaucoma: genetic, aqueous Humor blockage

• colorblindness: sex-linked genetic disorder, photo receptor absence