Lecture 8: Optic Disc Imaging, RNFL Analysis, & Ganglion Cell Analysis

Question 1

What is POAG?

Answer 1

• Optic neuropathy = atrophy of the optic nerve and loss of RGC
• loss of axons of the optic nerve fibers in the RNFL
• Damage to RNFL precedes observable changes to the optic nerve head (“cupping”)
• Significant RNFL loss can produce before functional loss (pre-perimetric)

Question 2

____ loss precedes ___ loss

• preceeds by __ years in __% of eyes
• As much as __-__% of RNFL may be lost before SAP VF changes apear
• Change in the cup represents loss of ____ of axons

Answer 2

structural; functional

• 6 years in 60% of eyes
• 30-50%
• thousands

Question 3

Describe the glaucoma continuum

Answer 3

Question 4

The fibers travel in an organized path

• Axons originating from ___ arc above or below arcades
  
  • Form inferior & superior rim
• Fibers from ___ retina insert into nasal rim
• Fibers from ___ insert into temporal rim
  
  • papillomacular bundle

Answer 4

• Temporal retina
• Nasal retina
• macula

Question 5

Which fibers are more (NOT most) resistant to glaucoma

Answer 5

fibers from nasal of of the retina come directly to the optic disc

Question 6

Which fibers are most resistant to glaucoma damage?

Answer 6

Fibers from the macular area come horizontally as the papillo macular bundle - keep vision centrally until the end

Question 7

Which fibers are the most sensitive to glaucomatous damage?

Answer 7

• Fibers from the temporal retina arch above and below the macula as superior and inferior arcuate fibers with horizontal raphe in between

Question 8

There is selective loss to the superior and inferior arcuate bundles - relative sparing of papillomacular and nasal bundles in (early/late) disease

Answer 8

early

Question 9

Slit defects occur in about __% of normals

Answer 9

10

Question 10

Wedge defects represent what?

Answer 10

represent expanding focal damage to the optic nerve

Question 11

What doe the image show?

Answer 11

slit defect

Question 12

What does the image show?

Answer 12

Pseudoslit defect

Question 13

What does this image show

Answer 13

wedge defect

Question 14

Thin NFL looks dark or bright?

Answer 14

dark

Question 15

VF defects appear in the more __ to __ levels of diffuse NFL loss

Answer 15

moderate to severe

Question 16

Quigley detected RNFL damage in __% of eyes with visual field loss but only in __% of normal eyes.

Answer 16

84%;3%

Question 17

RNFL photography has a sensitivity __% and a specificity __%

Answer 17

80%;94%

Question 18

OCT is used in both ___ and ___ of glaucoma

Answer 18

detection and analysis of progression

Question 19

What is the mean value of RNFL thickness in the general population?

Answer 19

92.9 um +/- 9.4

Question 20

a normal, nonglaucomatous eye has an RNFL thickness of >__um

Answer 20

80

Question 21

An average RNFL thickness of __-__um is suspicious for glaucoma

Answer 21

70-79

Question 22

Which test is best to discriminate healthy from glaucomatous eyes?

Answer 22

OCT

• sensitivity 84%; specificity 90%

Question 23

__% of glaucoma patient have visible NFL loss __-__ years before VF loss

Answer 23

60%; 4-6 yrs

Question 24

the axon loss is due to the ______ which is measurable by the OCT

Answer 24

ganglion cell dropout - indirect method of measuring

Question 25

In cases of paracentral which one has the BETTER ability to diagnose glaucoma, ganglion cell analysis or RNFL changes?

Answer 25

Ganglion cell analysis

Question 26

Average GCC thickness is between __ and __ um have been reported in normal eyes

Answer 26

68-74.8

Question 27

What does the ganglion cell complex include?

Answer 27

NFL, ganglion cell layer, inner plexiform layer

Question 28

What does the GCC measure?

Answer 28

measure thickness of 3-innermost retinal layers that are

Question 29

Thinning of GCA occurs most often on __ side and is more common in glaucoma with __ or __ VF defects

Answer 29

temporal, central, paracentral

Question 30

What is even based analysis?

Answer 30

• compare one test to another
  
  • Decide if amt of change is within measurement error
  • Approx 4um inter-visit reproducibility for SD-OCT (less than 10um for most OCTs)
  • be sure change is real, should be greatehr tahn 2x that or 8um (greater than 20um for most OCTs)
  • Should compare current test to the baseline tests; not the previous test (could miss slow progression)

Question 31

What is trend based analysis?

Answer 31

• looks at series of sequential tests and measures slope of change over time for whatever parameter you are looking at
• Primarily looks at rate of change rather than the amt
• less susceptible to fluctuation
• Requires a large number of tests (baseline test plus 2-3 subsequent test)
• Can not perform if testing on different machines

Question 32

What are 2 benefits of OCT-A?

Answer 32

• Diagnostic ability of peripapillary vessel density of OCTA especially the inferotempora sector measurement, found to be good in POAG and PACG
• Diagnostic abilities of vessel density measurements comparable to RNFL measurements in both POAG & PACG

Question 33

What are limitations of OCT-A (3)

Answer 33

• Lack of a normative database
• Large variation of retinal vasculature densities and blood flow that are likely present in the population
• Unclear whether systemic blood flow parameters or systemic anti-hypertensive medications would affect retinal vascular densities or retinal blood flow

Question 34

When is OCT most useful when evaluating glaucoma?

Answer 34

• Most useful when pt is glaucoma suspect, or has early to moderate disease
• Tool to detect damage and progression
• Can be quite helpful in early disease
  
  • In HVF plasticity and overlap inherent in visual system can compensate for early damage
  • Early damage may be picked up by OCT rather than VF (structural before functional change)
• Remember: in late diseae OCT is less useful due to “floor effect”