PHOTORECEPTORS

Rods

shades of gray in dim light
- 120 million
- Absent in fovea, more numerous in the periphery of the retina
- 6-600 : 1 bipolar cell

Cones

stimulated by brighter light; highly acute color vision
- Blue, green, red cones
- 6 million
- Most dense in fovea centralis (area of highest visual acuity) - 1:1 bipolar cell higher acuity

Anterior Cavity

Divided into an anterior chamber and a posterior chamber by the iris (colored portion of the eyeball).
- Both chambers are filled with aqueous humor (a clear, watery liquid)
- Contains aqueous humor that helps maintain the shape of the eyeball and supplies oxygen and nutrients to the lens and cornea

Posterior Cavity

Aka vitreous chamber
- Filled with vitreous humor (a transparent, gelatinous substance)

Cornea

Admits and refracts (bends) light

Sclera

Provides shape and protects inner parts

Fibrous Tunic

Cornea and Sclera

Iris

Regulates the amount of light that enters eyeball

Ciliary body

Secretes aqueous humor and alters the shape of the lens for near or far vision

Choroid

Provides blood supply and absorbs scattered ligh

Vascular Tunic

Iris, Ciliary body, and Choroid

Retina

Receives light and converts it into nerve impulses; provides output to brain via axons of ganglion cells, which form the optic (II) nerve

Lens

Refracts light

Vitreous Chamber

Contains the vitreous body, which helps maintain the shape of eyeball and keeps the retina attached to the choroid