Lec.2: Glaucoma Background, Basics and Concepts Flashcards
purpose of aqueous humor?
provides: shape, optical properties, nourishment to cornea and lens
name the muscles of the ciliary body muscle.
longitudinal fibers, circular fibers and radial fibers
what sit eh functional unit that is responsible for production of aqueous humor secretion?
ciliary process
what is hypotony?
soft eyeball that doesn’t maintain its shape
why is there an absence of protein and lipids in the aqueous fluid?
to enhance light transmission
in normal people, when is IOP highest and lowest?
highest in AM and lowest in PM
why may IOP spike in the PM for glaucoma patients?
because outflow may not be as good as the healthy patient
what enzymes are known to increase the production of aqueous?
Na/K-ATPase and carbonic anhydrase
what are the pathways of aqueous humor outflow?
trabecular (conventional) or uveoscleral (unconventional) route
name the route of the conventional route.
trabecular meshwork–> schelemm’s canal–> lumen –> collector channels–> aqueous veins –>episcleral venous circulation
how is aqueous humor outflow affected if there in an increase in pressure in the episcleral veins?
decreases. when laying down episcleral pressure is increased
which rout is can you quite readily decrease IOP?
conventional route
how long does it take to notice a large drop in uveoscleral outflow?
4-6 weeks
what is the percent of aqueous outflow by the trabecular route?
70-95% (main route)
what is the percent of aqueous outflow by the uveoscleral outflow? and which drug enhances outflow of this pathway?
5-30%
prostaglandin
is it true that both total and trabecular outflow increase with age?
false, they decline with age
what are the four parts that divide the optic nerve head?
surface nerve fiber layer, prelaminar region, lamina cribosa region and retrolaminar
in what part of the ONH are axonal bundles acquiring more interaxonal glial tissue?
surface nerve fiber layer
what is the predominant sructure of the prelaminar region?
nerve axons and astrocytes with signficant increase in astroglial tissue
what region of ONH has fenestrated sheets of scleral tissue that are separated by astrocytes?
lamina cribrosa
where in the ONH is there a decrease in astrocytes and myelin is acquired?
retrolaminar region
what is the main source of blood supply to the optic nerve?
posterior ciliary artery
what is the main blood supply to the surface NFL?
CRA (central retinal artery)
what is the main blood supply to the prelaminar and laminar regions?
SPCA (short posterior ciliary arteries) which then forms the circle of Zinn-Haller
in poor circulation, which vessels are more responsible for the decrease in circulation?
small vessels NOT the large vessels
which vessels cause sudden death of tissue in ischemic optic neuropathies?
large vessels
thin astrocytes accompany which axons?
axons in NFL
thick astrocytes accompany which axons?
direct axons from prelaminar to laminar region
what is found surrounding the myelin sheaths?
hyaluronate
how does increase in age and IOP affect hyaluronate?
hyaluronate decreases
how would the pores of the lamina cribrosa appear in an individual with glaucoma?
distorted or compressed pores
size of pores (from largest to smallest), follow which rule?
ISNT
what regions of the NFL do arcuate fibers (Bjerrum’s fibers) occupy?
superior and inferior temporal regions
do superior fibers cross into the inferior retina and vice-versa?
no. imagine a line that separates the two
approximately how many axons are we born with?
1 million
by what age does the ONH reach 95% of its full size?
1 yr old
is loss of axons based on size (largest are lost first)?
no
is cupping the absence of tissue?
yes
what does more cupping and less pallor indicate?
glaucoma
what is the extent of ocular damage in glaucoma?
associated with loss of the neurons that connect to the LGN or visual cortex
aside from increase IOP and low blood circulation, what else contributes to glaucoma?
aberrant immunity cells and excessive glutamate stimulation
which receptors does glutatmate overstimulate to kill off ganglion cells?
NMDA receptors and Kainate glutamate receptors
what endothelial cell secretes vasodilators?
nitric oxide
what endothelial cell secretes vasoconstrictors?
endothelin-1
why should you not use a fundus camera to asses c/d ratio?
uses post-processing of the data to adjust the colors (more pink). this leads to false estimates
what is considered to be an abnormal inter-ocular c/d asymmetry (between OD and OS)?
0.2 or greater
how much space should an optic nerve occupy in a 15 degree image?
5 degrees of the space
what condensing lens gives exactly 1x magnification (spares conversion factors)?
66D lens
what is considered a large nerve?
nerve larger than 2.5
what is considered a small nerve?
smaller than 1.5
what is considered a medium nerve?
1.5-2.0
how does a grey crescent affect estimation of the rim tissue?
leads to underestimation
in PPA (peripapillary atrophy) what does the widest region of the crescent correspond too?
thinnest rim tissue region
what is it called when a optic nerve is completely tilted 90 degrees?
tilted disc syndrome (ISNT rule wont work here)
what does the scleral lip represent?
represents anterior extension of sclera between choroid and optic disc
what is zone beta (chrioscleral crescent)?
broader, more irregular area of depigmentation. represents retraction of RPE and thinning or absence of choroid
what does a large zone beta indicate?
higher risk of glaucoma
where does rim tissue tend to be thinnest (in reference to zone beta)?
where zone beta is widest
what is zone alpha?
peripapillary crescent of increased pigmentation
why does PPA need to be monitored?
because it may increase over time (it is an indicator of glaucoma)
is presence of hemorrhage enough to initiate treatment for glaucoma?
no
what is barring?
rim becomes thinner and leaves an area (gap) or pallor between the rim and the circumlinear blood vessel
when is barring a “hard” sign of glaucoma.
is you dont see it when you first examine the patient, but after 3 years they develop barring
what is bayonetting (double angulation of blood vessel)?
vessels are observed going into the base of the cup, traveling up, and coming out of a different region
what is a last ditch effort to save the eye?
shunt vessels (due to obstruction of venous flow through distorted lamina cribrosa)
