Human Eye Anatomy and Visual Processing: Key Concepts and Pathways

Pupil

Expands in the dark (activated by SNS); constricts in the bright (activated by PSNS)

Cornea

Helps refract light to hit the retina filled with photoreceptors

Lens

Shape can be modified to help with focus

Macula

Middle of the retina; has the most cones; damage leads to blurred vision (peripheral vision not affected)

Fovea

Eye area with the most cones allowing high detail vision in daylight; located in the macula

Rods

1000 times more sensitive than any other photoreceptor; used to see at night; cannot see color

Cones

Used to see in the day; 3 types allow full spectrum of visible light; see in high detail

Horizontal cells

Refine photoreceptor signals by inhibiting neighboring photoreceptors while keeping one active to locate light source

Bipolar cells

Transport photoreceptor signals further toward retina output

Amacrine cells

Help refine signals coming from bipolar cells

Retinal ganglion cells

Take refined photoreceptor signals to the optic nerve which travels to the optic chiasm

Lateral geniculate nucleus

Located in the thalamus; relays visual information to the visual cortex

Optic chiasm

Two nerve pathways crossing to reach opposite visual cortex hemispheres; inner sides of eyes report contralaterally

Saccades

Rapid, ballistic eye movements shifting focus between points; essential for vision and reading

Dorsal stream

The 'where' visual pathway; processes spatial location and movement of objects

Ventral stream

The 'what' visual pathway; identifies objects and characteristics based on memory

macula degeneration

loss in detailed central vision, peripheral vision spared