Neuro-Ophthalmology Vol. 3 Flashcards
Approximately how many rods are found within the retina?
80 to 120 million
Approximately how many cones are found within the retina?
5 to 6 million
Where is the only place that rods are not found within the retina?
Fovea
Where is the physiologic blind spot located?
Approx. 17 degrees from the fovea
What is the average size of the physiologic blind spot?
5 by 7 degrees
What is the smallest subpopulation of cones?
Blue cones
What is the only type of cones NOT found at the fovea?
Blues cones
Where is the fovea located in relation to the optic disc?
4 mm temporal and 0.8 mm inferior to optic disc
What is approximate surface area of the retina?
2500 mm2
What calls connect the ganglion cells to the photoreceptors?
Bipolar cells
What is the most common type of ganglion calls?
Parvocellular (P cells; 80%)
What is the largest type of ganglion cells?
Magnocellular (M cells)
What type of ganglion cells are responsible for color perception and have low contrast sensitivity?
P cells
What type of ganglion calls are responsible for light contrast and motion?
M cells
What type of ganglion cells have the largest field of reception?
M cells
Where is the photoreceptor: ganglion cell ratio the highest?
Periphery (1000:1)
Where is the photoceptor:ganglion cell ratio the lowest?
Fovea (1:1)
Where is the concentration of ganglion cells the highest?
Macula
What causes the star-shaped pattern of macular edema?
Radial arrangement of axons of the bipolar cells (e.g. Henle layer)
What is the primary neurotransmitter of the retina?
Glutamate
What arteries make up the primary blood supply to the optic disc?
Posterior ciliary arteries
Where is the ophthalmic artery located in relation to the optic nerve within the optic canal?
The ophthalmic artery is located Inferior to the optic nerve within the optic canal
What bone makes up the optic strut?
Lesser wing of the sphenoid
What is the average length of the optic canal?
8 to 10 mm
What is the average width of the optic canal?
5 to 7 mm
In what direction does the optic canal course posteriorly?
Superior and medially
What is the most inferior portion of the frontal lobe?
Gyrus rectus (lies above and parallel to the optic nerves)
What is the average width and length of the optic chiasm?
12 x 8 mm
What is the average thickness of the optic chiasm?
4 mm
How far above the sella is the optic chiasm located?
Approx. 10 mm directly superior (though can be anterofixed or postfixed)
What percentage of the nasal fibers of the retina desiccate at the optic chiasm?
53%
What fibers of the retina are first to cross the optic chiasm?
Inferior fibers
Where is the lesion resulting in a superior temporal visual field defect with a central scotoma in the contralateral eye?
Junction of the optic nerve and chiasm
Where are the internal carotid arteries found in relation to the optic nerves?
The internal carotid arteries are located inferior to the optic nerves
What arteries provide the blood supply to the optic chiasm?
Proximal anterior cerebral and anterior communicating arteries
