Chapter 15

What structures make up the fibrous layer?

Sclera and cornea

Function of the sclera

Protects eye and maintains shape

Function of the cornea

Major site of light refraction

Structures of the vascular layer

Choroid, ciliary body, iris

Function of the choroid

Provides blood supply to eye

Function of the iris

Controls pupil size

Function of the ciliary body

Controls lens shape for accommodation

What makes up the neural layer?

Retina

Function of the retina

Contains photoreceptors that detect light

What are the photoreceptors of the eye?

Rods and cones

Functions of rods

Dim light, black/white vision, peripheral vision

Functions of cones

Color vision, sharp vision, bright light

Where are cones concentrated?

Fovea centralis

Location of best vision

Fovea centralis in the macula lutea

Why is the fovea centralis the area of best vision?

Highest concentration of cones and minimal light scattering

What is the optic disc?

Blind spot where optic nerve exits eye

What is aqueous humor?

Fluid in anterior cavity of eye

Function of aqueous humor

Nourishes cornea/lens and maintains pressure

What is vitreous humor?

Gel-like substance in posterior cavity

Function of vitreous humor

Maintains eye shape and supports retina

What is accommodation?

Changing lens shape to focus light

What happens to the lens during near vision?

Lens becomes rounder

What happens to the lens during distant vision?

Lens flattens

What is refraction?

Bending of light as it passes through substances

Main structure responsible for refraction

Cornea

Structure responsible for fine focusing

Lens

Pathway of light through the eye

Cornea → aqueous humor → pupil → lens → vitreous humor → retina → photoreceptors

What is rhodopsin?

Light-sensitive pigment in rods

What happens when light hits retinal?

Retinal changes shape

What happens during light adaptation?

Na+ channels close, photoreceptor hyperpolarizes, less neurotransmitter released

What happens during dark adaptation?

Na+ channels stay open and neurotransmitter is continuously released

What is bleaching?

Retinal separates from opsin after light exposure

Visual pathway to the brain

Photoreceptor → bipolar cell → ganglion cell → optic nerve → optic chiasm → optic tract → thalamus → visual cortex

What cranial nerve carries visual information?

Optic nerve (CN II)

What photoreceptors detect color?

Cones

Three cone types

Red, green, and blue cones

How is depth perception achieved?

Binocular vision from overlapping visual fields