W3 Retina & Fovea Specialisations

where does the retina terminate

at the ora serrata

what are the 10 layers of the retina

retinal pigment epithelium

photoreceptors

external limiting membrane

outer nuclear layer

outer plexiform layer

inner nuclear layer

inner plexiform layer

ganglion cell layer

nerve fibre layer

internal limiting membrane

where do the outer 5 layers of the retina receive their blood from

choriocapilliaris

where do the inner 5 layers of the retina receive their blood from

central retinal artery

which branch is the central retinal artery formed from

ophthalmic artery

what is the function of the rods

scotopic light

low light levels

high sensitivity

what is the function of the cones

photopic light

high acuity

low sensitivity

what are the wavelengths for the 3 cone VPs

S - 420

M - 534

L - 563

what are the wavelengths for rod VP

498

what does the visual pigment consist of

chromofore

+

protein

what is the chromofore

retinal

what is the protein

opsin

what is the isomer of the chromofore in the dark

bent 11-cis retinal

what is the isomer of the chormofore in the light

all trans retinal

what is the trigger for transduction

metarhodopsin II

why are cones not very sensitive to light

Visual pigments are inherently unstable and will occasionally isomerise even in the absence of light (thermal isomerisation).

To avoid telling the brain there is light there when there isn't, ganglion cells require input signalling ca. 5 isomerisations in order to fire.

This is unlikely to happen within the cone system in low light levels as the same cone, due to being connected to its own ganglion cell, will need to absorb 5 photons in order to activate that ganglion cell

The cone system will therefore not be activated in low light levels

what is spatial acuity

ability to resolve detail

what is acuity

ability to resolve 2 points

what are the 4 regions of the fovea

foveola

fovea

parafovea

perifovea

what are the carotenoids in the henle fibres

zeaxanthin

lutein

what is the role of carotenoid pigments

removes short wavelengths of light

improves image quality by removing wavelengths prone to chromatic aberrations

act as an antioxidant and removes damaging wavelengths

why is the foveola adapted for high acuity vision

inner 5 layers pushed away

avascular

carotenoid pigments