Avoiding Clinical Misinterpretation & Artifacts of OCT Analysis of ONH, RNFL, & GCL

Question 1

What were the conclusions of this study?

Answer 1

OCT is invaluable in Dx optic nerve disease, we need to be cognizant of the artifacts that can occur w OCT

Question 2

What is the benefit of Spectral Domain OCT over Time-Domain OCT?

Answer 2

It is FASTER and has HIGHER resolution

NOTE: time domain obtains 400 A-scans/sec while spectral domain OCT 20,000-40,000 A-scans/second, which provides an axial resolution on the order of 4-6 um

Question 3

Whats the benefit of running macular ganglion cell layer-inner plexiform layer (GCL-IPL) on OCT?

Answer 3

It helps us evaluate the cells that give rise to the optic nerve

Question 4

What has thinning of the macular GCL-IPL been shown to have strong relationship with?

Answer 4

Vision loss in optic nerve diseases:

1. Glaucoma
2. Optic neuritis
3. Ischemic optic neuropathy
4. Hereditary optic neuropathy
5. Toxic optic neuropathy
6. Optic nerve glioma
7. Idiopathic intracranial hypertension

Question 5

How many FP and artifacts has the spectral domain OCT been found to have?

Answer 5

FP: 26.2% (about 1/3)

Artifacts: 15-36% (about 1/4th)

Question 6

What are factors that canc onfound the RNFL analysis?

Answer 6

1. Incorrect age
2. Poor signal strength
3. Inaccurate segmentation of the retinal layers
4. Long or short axial eye lengths
5. Interindividual differences
6. Cyclotorsion
7. PPA
8. Ocular diseases that can cause artifactual INC in RNFL thickness, and diff in the RNFL thickness in normals

Question 7

How does RNFL change with age?

Answer 7

RNFL thickness on OCT DECREASES by 0.365 um/year

Question 8

How does a reduction in signal strength from media opacities or optic nerve edema affect OCT interpretations?

Answer 8

Loss of retinal layer features, intraretinal hypodensity, and artifacts in layer segmentation and interpretation

Question 9

What are the most common causes of media opacities that affect OCT strength?

Answer 9

1. Dry eyes
2. Corneal opacities
3. Cataracts
4. Vitreous opacities

Question 10

What did Vizzeri et al find about the relationship between signal strength & mean RNFL thickness among healthy patients analyzed w Stratus OCT?

Answer 10

(+) linear relationship

Each unit of DEC in SS, the average RNFL thickness had a corresponding DEC of 2 um

Question 11

Once signal strength drops below x/10 in the Cirrus platform, the segmentation algorithm can sometimes fail and produce large regional errors in derived RNFL thickness?

Answer 11

7!!!!!

Question 12

What will optic nerve head edema do to OCT findings?

Answer 12

1. Block our ability to find the full extent of the underlying Bruch’s membrane and its termination at the neural canal opening –> disc area may look LARGER!!!!
2. Distortion of the retinal layers

Question 13

Where else can errors in segmentation be seen by examining?

Answer 13

the TSNIT curve

NOTE: a 0 um on the TSNIT RNFL thickness plot can only be due to segmentation error

Question 14

What can a vitreous opacity be incorrectly identified as? How does it affect RNFL measurements?

Answer 14

Internal limiting membrane

Artifactually thickened RNFL measurements

Question 15

How can errors in segmentation occur?

Answer 15

Decentering the scan in the z-axis

This can cause truncation of the image –> absolute loss on the RNFL thickness plot

Question 16

When is decentering the scan in the z-axis a particular problem?

Answer 16

1. Significant disc edema
2. Tilted disc
3. Sig cupping bc the peripapillary RNFL may be difficult to capture on a single B scan due to diffs in height btwn the opposite sides of the circular RNFL scans

NOTE: decentering can cause scans to have an area of truncation (shortening)

Question 17

How does axial length of the eye effect RNFL?

Answer 17

Higher axial length=myopia=THINNER RNFL