Identifying and understanding optical coherence tomography artifacts that may be confused with glaucoma

Optical coherence tomography is often used for detection of glaucoma as well as to monitor progression. This paper reviews the most common types of artifacts on the optical coherence tomography report that may be confused with glaucomatous damage. We mainly focus on anatomy-related artifacts in which the retinal layer segmentation and thickness measurements are correct. In such cases, the probability maps (also known as deviation maps) show abnormal (red and yellow) regions, which may mislead the clinician to assume disease is present. This is due to the anatomic variability of the individual, and the normative database must be taken into account.

Glaucoma; Artefacts; Tomography, optic coherence

Authorship

Ari Leshno

Bernard and Shirlee Brown Glaucoma Research Laboratory, Edward S. Harkness Eye Institute, Department of Ophthalmology, Columbia University Irving Medical Center, 635 W 165th St, New York, NY, USA 10032.Columbia UniversityUSANew York, NY, USABernard and Shirlee Brown Glaucoma Research Laboratory, Edward S. Harkness Eye Institute, Department of Ophthalmology, Columbia University Irving Medical Center, 635 W 165th St, New York, NY, USA 10032.

Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.Tel Aviv UniversityIsraelTel Aviv, Israel Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.

http://orcid.org/0000-0002-8717-1659

Donald C. Hood

Department of Psychology, Columbia University Schermerhorn Hall, 1190 Amsterdam Ave #406, New York, NY, USA 10027.Columbia UniversityUSANew York, NY, USA Department of Psychology, Columbia University Schermerhorn Hall, 1190 Amsterdam Ave #406, New York, NY, USA 10027.

http://orcid.org/0000-0001-6717-4791

Jeffrey M. Liebmann

http://orcid.org/0000-0002-5663-0533

Carlos Gustavo De Moraes

http://orcid.org/0000-0002-5626-0894

Corresponding author: Carlos Gustavo De Moraes, MD, MPH, PhD 635 W 165th St, Box 69, Zip code: – New York, NY, 10032, USA E-mail: cvd2109@cumc.columbia.edu

Institution: Columbia University Irving Medical Center New York, NY, USA

Conflict of interest:the authors declare no conflict of interest.

SCIMAGO INSTITUTIONS RANKINGS

Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.Tel Aviv UniversityIsraelTel Aviv, Israel Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.

Figures

Figures (7)

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Figure 1
Proposed anatomical model. Simulated examples of arcuate-like artifacts due to misalignment of the average normative data with the measured retinal nerve fiber thickness. (A) Average thickness from normative data with proper alignment. (B) Simulation of nasal shift of superior retinal nerve fiber bundle. (C) Simulation of temporal shift of the disc center. (D) Simulation of cyclorotation (head tilt).

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Figure 2
Arcuate-shaped retinal nerve fiber defects due to anatomic variation on major bundle location. (A) Topcon Hood report from a 23-year-old healthy subject scanned with the Triton Swept Source optical coherence tomography device. The retinal nerve fiber probability map shows significantly thinner arcuate-shaped areas in both the inferior and superior hemifields, resembling retinal nerve fiber defects (red arrows). However, a carefull look at the retinal nerve fiber thickness map shows a relatively thick yet temporally displaced retinal nerve fiber (black arrows). The black borders on both of these maps indicate an iso-thickness (75µm) border of the average thickest retinal nerve fiber around the disc. As predicted by a simple model, these arcaute-like defects in healthy eyes fall within this black border. This simple model also predicts that there should be a thicker than normal region. This can be seen to be the case in the report in B which shows significantly thicker regions. (B) Heidelberg Hood report from the same patient scanned with the Spectralis spectral-domain optical coherence tomography device on the same day. The probability maps here also show areas of significant thickening (blue-purple). Notice that in the inferior hemifield there is a “super-thick” area adjacent to the arcuate-shaped artifact. Both are due to the anatomical variation of major blood vessels and retinal nerve fiber bundles. This Hood report is avialable only for research purposes in some countries (e.g., the United States).

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Figure 3
Deviation in disc centering. In order to simulate the effect of improper disc-centering on the probability map, the same scan was used to generate three different reports. In each of the three reports, the black outline indicates the location of the disc-center on the retinal nerve fiber maps (thickness and probability) defined for analysis and comparison with normative data. (A) Proper disc centering. (B) Temporal displacement of disc center resulting in both arcuate-shaped artifacts as well as temporal defects on the retinal nerve fiber probability map. Notice how the major retinal nerve fiber bundle peaks (orange arrows) move farther apart on the cpRNFL plot (red arrows) and how the average thickness on the pie-charts changes. (C) Nasal displacement of disc center resulting in a minor arcuate-shaped artifact in the inferior hemifield as well as some artifacts on the nasal half of the disc. Notice how the major retinal nerve fiber bundle peaks (orange arrows) move closer to each other on the cpRNFL plot (red arrows).

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Figure 4
Artifacts due to uncorrected cyclotorsion/ head tilt. (A) Report of a healthy 26-year-old individual showing a normal retinal nerve fiber thickness map. (B) In a subsequent visit, an arcuate-shaped retinal nerve fiber defect appears in the superior hemifield (red arrow) suggesting progression (note also the red in the 7th clock-hour pie chart corresponding to the same location). However, a more careful examination reveals that the retinal nerve fiber thickness did not change except for some counter-clockwise rotation, which resulted in an increase of the fovea-to-disc angle (white lines). Notice also that the cpRNFL thickness line remained the same, but the thickness map appears to have shifted slightly to the right (horizontal yellow arrow). This was most likely due to head-tilt and cyclotorsion, which resulted in the observed artifact. Moreover, most of the artifact falls within the black outline as predicted by the anatomical model.(14)

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Figure 5
Example of a circum-foveal artifact. (A) Circum-foveal artifact: “abnormal” regions (<1%, red) largely within the central ±4° (white dashed circle) in both hemi-retinas. Both 24-2 and 10-2 visual field test performed on the same day as the scan verify that there is no functional abnormality scan. (B) Example of central foveal dot-artifact (red arrow) in an otherwise normal.

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Figure 6
Artifacts due to an incorrect date of birth. Heidelberg optical coherence tomography report of a healthy 73 year old patient. (A) The report with the proper date of birth showing a normal apearing retinal nerve fiber and ganglion cell layers without any significantly thin areas on the probability maps. (B) The same scan but the report produced with the wrong date of birth, making the patient “younger” by 51 years (22 instead of 73). Notice the temporal retinal nerve fiber “defects” (red arrows) become thicker and more obvious with a more significant change on the ganglion cell layers probability map. The cpRNFL pie chart also becomes yellow and red in the temporal half.

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Figure 7
Lower end of normal. Example of the difficulty in differentiating, glaucoma from healthy eyes that fall within the lower fifth percentile of the normative database. The optical coherence tomography reports taken from two different individuals show very similar patterns on the retinal nerve fiber probability map (top right) and cpRNFL thickness plot (top left). Even though it is based on the retinal nerve fiber thickness map, it is hard to determine which eye is healthy and which one suffers from diffuse damage. However, a closer look at the ganglion cell layers thickness reveals that while the healthy eye has a rather uniform ganglion cell layers (A), the glaucomatous eye (B) has a patchy pattern, suggesting areas of focal damage.

Figure 1 Proposed anatomical model. Simulated examples of arcuate-like artifacts due to misalignment of the average normative data with the measured retinal nerve fiber thickness. (A) Average thickness from normative data with proper alignment. (B) Simulation of nasal shift of superior retinal nerve fiber bundle. (C) Simulation of temporal shift of the disc center. (D) Simulation of cyclorotation (head tilt).

Figure 2 Arcuate-shaped retinal nerve fiber defects due to anatomic variation on major bundle location. (A) Topcon Hood report from a 23-year-old healthy subject scanned with the Triton Swept Source optical coherence tomography device. The retinal nerve fiber probability map shows significantly thinner arcuate-shaped areas in both the inferior and superior hemifields, resembling retinal nerve fiber defects (red arrows). However, a carefull look at the retinal nerve fiber thickness map shows a relatively thick yet temporally displaced retinal nerve fiber (black arrows). The black borders on both of these maps indicate an iso-thickness (75µm) border of the average thickest retinal nerve fiber around the disc. As predicted by a simple model, these arcaute-like defects in healthy eyes fall within this black border. This simple model also predicts that there should be a thicker than normal region. This can be seen to be the case in the report in B which shows significantly thicker regions. (B) Heidelberg Hood report from the same patient scanned with the Spectralis spectral-domain optical coherence tomography device on the same day. The probability maps here also show areas of significant thickening (blue-purple). Notice that in the inferior hemifield there is a “super-thick” area adjacent to the arcuate-shaped artifact. Both are due to the anatomical variation of major blood vessels and retinal nerve fiber bundles. This Hood report is avialable only for research purposes in some countries (e.g., the United States).

Figure 3 Deviation in disc centering. In order to simulate the effect of improper disc-centering on the probability map, the same scan was used to generate three different reports. In each of the three reports, the black outline indicates the location of the disc-center on the retinal nerve fiber maps (thickness and probability) defined for analysis and comparison with normative data. (A) Proper disc centering. (B) Temporal displacement of disc center resulting in both arcuate-shaped artifacts as well as temporal defects on the retinal nerve fiber probability map. Notice how the major retinal nerve fiber bundle peaks (orange arrows) move farther apart on the cpRNFL plot (red arrows) and how the average thickness on the pie-charts changes. (C) Nasal displacement of disc center resulting in a minor arcuate-shaped artifact in the inferior hemifield as well as some artifacts on the nasal half of the disc. Notice how the major retinal nerve fiber bundle peaks (orange arrows) move closer to each other on the cpRNFL plot (red arrows).

Figure 4 Artifacts due to uncorrected cyclotorsion/ head tilt. (A) Report of a healthy 26-year-old individual showing a normal retinal nerve fiber thickness map. (B) In a subsequent visit, an arcuate-shaped retinal nerve fiber defect appears in the superior hemifield (red arrow) suggesting progression (note also the red in the 7th clock-hour pie chart corresponding to the same location). However, a more careful examination reveals that the retinal nerve fiber thickness did not change except for some counter-clockwise rotation, which resulted in an increase of the fovea-to-disc angle (white lines). Notice also that the cpRNFL thickness line remained the same, but the thickness map appears to have shifted slightly to the right (horizontal yellow arrow). This was most likely due to head-tilt and cyclotorsion, which resulted in the observed artifact. Moreover, most of the artifact falls within the black outline as predicted by the anatomical model.(14)

Figure 5 Example of a circum-foveal artifact. (A) Circum-foveal artifact: “abnormal” regions (<1%, red) largely within the central ±4° (white dashed circle) in both hemi-retinas. Both 24-2 and 10-2 visual field test performed on the same day as the scan verify that there is no functional abnormality scan. (B) Example of central foveal dot-artifact (red arrow) in an otherwise normal.

Figure 6 Artifacts due to an incorrect date of birth. Heidelberg optical coherence tomography report of a healthy 73 year old patient. (A) The report with the proper date of birth showing a normal apearing retinal nerve fiber and ganglion cell layers without any significantly thin areas on the probability maps. (B) The same scan but the report produced with the wrong date of birth, making the patient “younger” by 51 years (22 instead of 73). Notice the temporal retinal nerve fiber “defects” (red arrows) become thicker and more obvious with a more significant change on the ganglion cell layers probability map. The cpRNFL pie chart also becomes yellow and red in the temporal half.

Figure 7 Lower end of normal. Example of the difficulty in differentiating, glaucoma from healthy eyes that fall within the lower fifth percentile of the normative database. The optical coherence tomography reports taken from two different individuals show very similar patterns on the retinal nerve fiber probability map (top right) and cpRNFL thickness plot (top left). Even though it is based on the retinal nerve fiber thickness map, it is hard to determine which eye is healthy and which one suffers from diffuse damage. However, a closer look at the ganglion cell layers thickness reveals that while the healthy eye has a rather uniform ganglion cell layers (A), the glaucomatous eye (B) has a patchy pattern, suggesting areas of focal damage.

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Identifying and understanding optical coherence tomography artifacts that may be confused with glaucoma

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[1] Corresponding author: Carlos Gustavo De Moraes, MD, MPH, PhD 635 W 165th St, Box 69, Zip code: – New York, NY, 10032, USA E-mail: cvd2109@cumc.columbia.edu