L16 Specialised areas of the Retina Flashcards
When examining the fundus (back surface of the eye), what do you examine?
Quality of the optic nerve
Thickness of the retina
Quality of the fovea - positioning
Blood vessel - positioning > branching out in arcuate way, none in foveal area and mascula
What is the foveal position from the optic disc?
11.8˚ or 3.4mm temporal to the optic disk edge.
When foveal area is swollen, the foveal position may change (distant)
What is the distance (angle) from macula (centre) to fovea?
5.2˚
What does the macula include?
Perifovea, parafovea, foveal pit, foveal slope, and fovea
OCT test is used to look at
Fundus - layers of the retina.
If photoreceptor layer is discontinuous RPE, its an emergency
What is the macula lutea?
- Yellow-pigmentation in the macular region, more specifically in the cone axons of the Henle fibres. Thus, we see yellow around the fovea
- Thought to act as a short wavelength filter
- Protective mechanism for avoiding bright light and esp UV radiation damage
What is the yellow pigmentation a reflection from?
Pigments, xanthophyll (obtained from fruits adn veges), carotenoids (carrots), xeaxanthin and lutein present in the cone axons of the Henle fibre layer.
What are the features of foveal cone cells?
Thin, slender, densely packed, and light gets directly to cone cells
Look like rods
What’s the difference between central and peripheral retina?
- Presence of henle fibres in fovea. In periphery, cone and rod cells make contact with INL directly
- OPL of central retina is thicker than peripheral retina
- Difference in thickness of the synaptic layer (IPL and OPL)
- Presence of macula lutea pigment in central retina
What is the total number of cones in fovea?
200000 approx, 17500 cones per degree^2. Fovea is about 1-2˚.W
What is the total number of cones in the retina?
6,000,000
Total number of rods in the retina?
110,000,000 to 125,000,000
- high rod density in peripheral
Ora Seratta:
- Is an area that leads (transition) from retina to ciliary body
- Neural retina continuous with non-pigmented ciliary epithelium
- RPE continuous with pigmented epithelium of CB
What are ganglion cells?
Axons that project out as the optic nerve
Optic nerve is attached _____ and ____ (edge of eye to end of orbit) - optic nerve is attache to rectal muscles as they pass back into orbit.
intraocularly, intraorbitally
Optic nerve is on the ___ side of the eye
Nasal
The optic nerve is bundles of ganglion cell axons that exit the eye - CN__?
2
What is the nerve fibre layer?
Axons of ganglion cells that form bundles that then pass down optic nerve
Optic nerve myelination?
Axons are unmyelinated in the anterior part, but become myelinated in the optic nerve
The optic nerve is surrounded the 3 meningeal layers….
Pia mater, Arachnoid mater, Dura mater
What does the lamina cribrosa do?
A layer in the optic nerve that supports it and keeps it in place
Nerve fiber locations:
- Nasal fibres will be located medially at the end of the optic nerve as they decussate at the chiasm.
- Before deccusation, nasal fibres are located on the left side of the optic nerve.
What is a horizontal raphe?
A line that divides the retina into superior and inferior regions, as the collate to go into the optic nerve.
What is the nerve fibre pattern?
Optic nerve head is where all the axons are joined together, continue to form the optic nerve - not formed randomly. Those fibres close to fovea and macula come directly to optic nerve head on the temporal side. Those further apart will form an arcuate and pass through the superior and inferior part.
At optic nerve: macular is on the side, taking up large area, with ST, SN, IN, IT.
Proximal to chiasm: macular region is in the centre, surrounded by ST, SN, IT, IN.
What is the significance to the optic nerve pattern?
Partial damage to optic nerve causes localised visual field defects, superior inferior, temporal, nasal, central vision loss.
