Photoreceptors

Which layer of the retina contains photoreceptors?

Outer Nuclear Layer

Inner Segment

Outer Segment

Retinal Signal Sequence

Light gets absorbed by photoreceptors(rods and cones)

Photoreceptors signal bipolar & horizontal cells

Bipolar & horizontal cells signal amacrine cells

Amacrine cells signal ganglion cells

Ganglion cells signal LGN & Visual Cortex

LGN

Lateral Geniculate Nucleus

Rod vs Cone(anatomy)

Neurotransmitter segment called spherule in rods, pedicle in cones

Outer segment "stack of coins" in rods, pyramid in cones

Disk Shedding/Phagocytosis

RPE breaks down outermost segment and remnants

Disk completely renewed every ~14 days

RPE

Retinal Pigment Epithelium

Monolayer of cells which breakdown outermost disc of photoreceptor for renewal and maintenance

Dysfunction in RPE leads to Drusen

Rods vs Cones(count)

Rods ~120mil, cones ~6mil

Rods vs Cones(peak density)

Rods ~20degrees(absent in fovea), cones 0degrees

Rods vs Cones(time response)

Rods slow, cones fast

Rods vs Cones(directionality)

Rods no directionality sensitive to scattered light, cones yes sensitive to direct light

Rods vs Cones(temporal resolution)

Rods low ~12Hz, cones high ~60Hz

Rods vs Cones(light sensitivity)

Rods HIGH, cones low

Rods vs Cones(spatial sensitivity)

Rods low, cones high

Direct link to VA

Rods vs Cones(dark adaptation)

Rods ~30-40mins, cones ~10mins

What is the pigment in rods?

Rhodopsin

Retinal Eccentricity

The distance from the fovea expressed in mm or degrees

Photoreceptor Size and Eccentricity

Cone size increases with eccentricity

What are the pigments in cones?

Cyanolabe, chlorolabe, and erythrolabe

Rhodopsin

Maximal light absorption at 507nm

Cyanolabe

Maximal light absorption at 426nm

Found in S-cones

Chlorolabe

Maximal light absorption at 530nm

Found in M-cones

Erthyrolabe

Maximal light absorption at 560nm

Found in L-cones