Glx Primer Flashcards
What is glaucoma?
Optic neuropathy + visual function loss
What is optic neuropathy?
Excavation and undermining of neural and connective tissue of optic disc; eventual development of VF defects
GCA damaged at LC w/ retrograde atrophy
What percentage of optic nerve fibers are lost before measurable VF loss occurs?
20-40%
What is pre-perimetric glaucoma?
Glaucomatous optic disc changes in pts w/ normal VF as determined by SAP
Ophthalmoscopic exam techniques
Optic disc size C/d ratio Loss of rim tissue Disc hemorrhage Peripapillary atrophy RNFL atrophy
Stereoscopic highly magnified view thru a dilated pupil:
- prefrontal lens: 78/60/90
- fundus CL aka Gonio
- Hruby lens
Non-stereo view relies on
Color cues
Can underestimate c/d
Stereoscopic view relies on
Contour cues
Which statement(s) is true? A. Number of RGC axioms entering optic nerve is fairly constant. B. The diameter of the scleral foramen varies widely. C. The diameter of the optic disc also varies widely. D. The smaller the scleral foramen, the smaller the optic cup.
All true
Diameter of the optic discs is governed by diameter of scleral foramen.
What is the mean vertical diameter of the disc? Horizontal?
Vertical: 1.9mm (range 1.0-3.0mm)
Horizontal: 1.75mm ( range 0.9-2.6mm)
What is the first step in assessment of optic cup size?
Assessment of disc size
Axonal tissue entering disc varies much less than size of disc itself - cup size can vary greatly w/o necessarily reflecting any underlying deficit in number of ganglion cells
How can you estimate physiological disc size?
Measure vertical diameter w/ indirect fundus lens method; digital imaging is more precise.
Steps in analysis of vertical CDR
- What is vertical CDR?
- What is the inferior rim-to-disc ratio?
- What is the sup?
- Do you want to reassess your initial impression of the vertical CDR?
It is best to use color and other monocular cues to locate cup margins. True or false?
False - tends to underestimate cup size
Use Stereopsis and mag w/ Biomicroscope! (Contour of rain tissue and deflections of blood vessels)
Difficultly in locating cup margin
- sloping rim tissue
- oblique ON insertion d/t high myopia
Difficulty in locating disc margin
- scleral ring
- peripapillary crescents and atrophy
- blurred or irregular disc margins
CDR is satisfactory in assessing glaucoma status. True or false?
False - lots of overlap in normal/glx suspect/glx groups
Which parts of the optic disc are more susceptible to glaucoma?
IT > ST
Can lead to vertical or oblique enlargement of optic cup
IT loss of neural rim can lead to:
- sharpened rim at disc margin
- sharpened polar nasal edge
- bayoneting at disc edge, where vessels cross the sharpened rim
- laminar dot sign d/t exposure of fenestrated in lamina cribosa
Rim loss may be diffuse, but is more often localized to sup/inf poles
Highly localized rim loss = notch
Describe pallor/cup discrepancy
In early glaucoma, enlargement of the cup may progress ahead of the area of the pallor. A potential error is to look only at the area of pallor and miss the large area of cupping. The neuro retinal rim does not develop pallor in glx optic neuropathy.
What is a significant predictor of glaucoma?
Violation of ISNT rule
What causes generalized enlargement and deepening of the cup?
Diffuse loss of ganglion cell axons rather than focal damage
Why is it difficult to detect generalized cup enlargement clinically?
Still round and obeys ISNT
*IMPORTANT to compare symmetry/asymmetry between eyes
Deepening of the cup
Exposure to underlying LC - seen as laminar dot sign
Advance glaucoma - back-bowing of LC, appears as “bean pot” - can result in vessel deflections
Splinter/“Drance” hemorrhages
Crosses disc margin Transient and resolves w/ time FIRST SIGN of glaucomatous damage More frequent in NTG>POAG Sign that glx is out of control Increased rate of glx progression NOT pathognomonic to glaucoma Often subtle and frequently overlooked Higher rates of detection w/ photography
Sign of peripapillary atrophy
Scleral ring - Border tissue of Elschnig
NOT part of optic disc and should NOT be included in C/D calc
NOT pathognomonic for glx - but greater in eyes w/ glaucoma; risk factor for conversion of OHT->POAG
Zone beta more strongly asso w/ glx - no RPE
____ is useful in the early detection of glaucoma.
Examination of NFL - NFL defects may preced VF loss and structural ONH changes
RNFL atrophy ddx
Glx or neurological disorders (MS)
Ophthalmoscopy for RNFL
Bright light, red-free filter (RPE and choroid absorb green light to create a dark bg; RPE and choroid - brighter?)
NFL is most visible in heavily pigmented eyes
Defects = dark stripes, wedge shaped defect in peripapillary area, or diffuse loss of striations
What is required for a glaucoma diagnosis?
Optic nerve damage = optic neuropathy
Cannot be diagnosed w/ a tonometer/IOP! - IOP is one of the primary risk factors
Glaucomatous optic neuropathy is a result of…
IOP AND resistance of optic nerve axons to pressure damage
What is the most important risk factor for glaucoma and the only one that can be effectively altered?
IOP
Decreasing IOP decreases the incidence of glaucoma. True or false?
True
Decreasing IOP can slow progression of OAG. True or false?
True
What are the three factors that determine IOP?
- rate of AH prod
- resistance to AH outflow across TM-SCHLEMM (specifically juxtacananlicular meshwork)
- EVP
*elevated IOP is ALMOST ALWAYS a consequence of increased resistance to outflow
Outflow facility incr/decr w/ age.
Decreases
Outflow facility can be affected by surgery, trauma, meds, endocrine factors. True or false?
True
Patients w/ glaucoma and elevated IOP have incr/decr facility of outflow.
Decreased
Which of the two major mechanisms of outflow limits backflow?
Trabecular
Trabecular outflow can be increased pharmacologically and surgically. Name the pharmacological agents and surgeries.
- ROCK (new)
- Parasympathetics (Pilo - highly effective but lots of side effects)
- Epinephrine compounds (low effectively - no longer used)
- trabeculoplasty/trabeculectomy (filtering bleb/opening)
Trabecular meshwork outflow
TM - schlemm’s - episcleral veins
UveoScleral outflow
AC - ciliary muscle - supraciliary and suprachoroidal spaces - intact sclera or along nerves and vessels that penetrate sclera
Uveoscleral outflow can be increased pharmologically and surgically. True or false?
False - can’t surgically
Pharm:
- prostaglandin analogs (lots of side effects)
- alpha-adrenergic agonists (dual-action effect: decr prod/incr outflow)
USO may also increase (IOP decrease) in pts w/ rhegmatogenous RD and cyclodialysis.
Fluctuation in IOP is a risk factor for optic nerve damage. True or false?
True
IOP peaks at night - what is measured in clinic is not ascertained
Trans-lamina cribosa pressure difference (TLPD) depends on…
Pressure difference between IOP and orbital CSFP
High IOP and low CSFP increases risk of glaucoma
High IOP + normal CSFP = POAG
Normal IOP + low CSFP = NTG
High IOP + high CSFP = OHT
Low IOP + high CSFP = papilledema
