Physio - Vision

Location - outer layer of eyeball

Function - give shape to eyeball

(Composed of sclera, cornea and conjuctiva)

Location - posterior outer layer/white of the eye

Function - supports and protects eyeball

Location - anterior surface of eyeball

Function - transmits and refracts light

Location - middle layer of eyeball

Function - supplies blood; prevents reflection

(Composed of choroid, ciliary body and iris/pupil)

Locaton - middle layer in posterior portion of eyeball (lies between sclera and neural layer)

Function - supplies blood to eyeball

• -highly pigmented and vascular
• -absorbs light (prevents it from bouncing around in eye)

Location - anterior portion of vascular tunic

Function - supports the lens through suspensory ligament and determins its thickness; secretes aqueous humor

Location - anterior portion of vascular tunic; continuous with ciliary body

Function - regulates the diameter of the pupil, and hence the amount of light entering the vitreous chamber

Controlled by the ANS

(pupil is hole in iris)

• (also contains pigment producing cells)
• -lots = dark brown eyes
• -less = other colors

Location - inner layer of eyeball

Function - provides location and support for rods and cones(pigmented epithelium)

(Composed of retina)

Location - principal portion of internal tunic

Function - photoreception; transmits impulses

Area with very high density in cone cells

Location - center of macula lutea

Function - light is focused here

Area where no rods or cone cells exist

Location - between posterior and vitreous chambers; supported by suspensory ligament of ciliary body

Function - refracts light and focuses onto fovea centralis

Eyes are "transducers"

• detect visible light
• this changes membrane potential
• sends electrical signals to other retinal neurons
• ultimately action potentials send to brain

• fills anterior spaces of eye (anterior to lens)
• produced by ciliary body
• nourishes lens and corneal cells
• constantly produced and drained (via Canal of Schelm)

• fills posterior spaces of eye (behind the lens)
• critical function: support retina

Light bends when it passes through different media

• Ability to change the focus of light on the retina
• We accommodate by changing the shape of the lens (ciliary body)

Sharpness of vision (ability to distinguish 2 objects at a distance)

Used to test visual acuity

20/20 - normal vision: you see at 20 ft what a person sees at 20 ft

20/15 - better than normal: you see at 20 ft what a person sees at 15 ft

20/30 - worse than normal: you see at 20 ft what a person sees at 30 ft

Normal Vision

Rays focus on retina

• Nearsighted
• Long eyeball
• Rays focus in front of retina
• Concave lenses needed

• Farsighted
• Short eyeball
• Rays focus behind retina
• Convex lenses needed

• Loss of elasticity
• Comes with age
• Reading glasses needed

• Uneven lens or distortion in lens
• Rays do not focus
• Uneven lens correctd astigmatism