Optic nerve head Flashcards
What are the four parts that the optic nerve head is divided into
- Surface nerve fiber layer
- Prelaminar region
- Lamina cribrosa region
- Retrolaminar region
What consists of the surface nerve fiber layer
innermost portion, predominantly nerve fiber, axonal bundle acquire more ineraxonal glial tissue as this structure is followed posteriorly
What is the prelaminar region
Nerve axons and astrocytes with significant increase in astroglial tissue
What is lamina cribrosa
Continuation of the sclera. Has fenestrated scleral tissue. Astrocytes sep. the sheets and line the holes. Bundle of axons leave through these holes
What is the retrolaminar region
Decrease in astrocytes, myelin is acquired. Axonal bundles surrounded by connective tissue. Posterior limit is not clear but about 3 to 4 mm
Vasculature of the optic nerve head
arterially: posterior ciliary artery, except for nerve fiber layer which is supplied by retinal circulation
Blood vessel to optic nerve
Through the central retinal artery
Blood vessel supply to surface nerve fiber layer
main supply arterioral branches of central retinal artery. anastomize with the vessels of the prelaminar region
Blood vessel supply to prelaminar and laminar regions
Primary supply: short posterior ciliary arteries. Forms circle of zinn-haller. also supply peripapillary choroid
Blood vessel supply to retrolaminar region
medial and lateral perioptic nerve short posterior ciliary artery
Form an elliptical arterial circle around the optic nerve (also called circle of zinn haller)
Where are the capillaries derived from
Both retinal and ciliary circulation. Resemble retinal capillaries. Don’t leak fluorescein and may represent nerve blood barrier. Decrease in number posterior to lamina
Where does venous drainage occur
Through the central retinal vein
What does astroglial support do
Provides continuos layer between nerve fiber and blood vessels of optic nerve head.
What do the thin astrocytes do
Accompany the axons in the nerve fiber layer
What do the thick astrocytes do
Direct axons from prelaminar to laminar region
Where does glaucoma pathogenesis take place
lamina cribrosa
Where is the porous region of the sclera
lamina cribrosa
T/F Hyaluronate decreases with age and with increase in IOP
TRUE
What determines a healthy analysis of pores in lamina cribrosa
Round in eyes with physiologic cupping
How are the lamina pores superiorly what about inferiorly. what about nasally and temporally
Superiorly and inferiorly: Larger
Nasally and temporally: smaller
Where do the arcuate fibers occupy
Superior and inferior temporal regions
Which fibers spread approx 1/3 of the distal optic nerve primarily inferior temporal
papillomacular fibers. It also intermingles with extramacular fibers (may explain retention of central vison)
How many axons are there
70,000 to 1.2 million. Inc with inc in area
What is the influence of age in regards to the optic nerve head
The size of the onh is 95% before age 1.
