J Korean Ophthalmol Soc.  2009 Apr;50(4):558-564. 10.3341/jkos.2009.50.4.558.

Analysis of Localized Retinal Nerve Fiber Layer Defects not Detected by Optical Coherence Tomography

• Han YS
• Jea SY
• Kim SJ
• Lee JE
• Lee JE
• Koo GH

• KMID: 2212257
• DOI: http://doi.org/10.3341/jkos.2009.50.4.558

Abstract

PURPOSE: To analyze localized RNFL defect cases that were identified in retinal nerve fiber layer (RNFL) fundus photographs but not in optical coherence tomography (OCT).
METHODS
Analysis of OCT scans and images was performed for 14 eyes (17 locations) that showed localized RNFL defects in RNFL fundus photographs but not in RNFL thickness average analysis.
RESULTS
With respect to the range of RNFL defects, 41.2% were less than 10degrees, 47.0% were 11 to 20degrees, and 11.8% were 21 to 30degrees. In 71.4% of the RNFL cases the defects were less than 10degrees and the decrease of RNFL thickness was not readily observable on the OCT scan images. In all cases of RNFL defects in the 11 to 30degrees range the decrease in RNFL thickness could be assessed on the OCT scan images. Nonetheless, the decrease of RNFL thickness could not be seen on the OCT analysis images in which the results of the RNFL thickness made through an automated computer algorithm were displayed.
CONCLUSIONS
The range of localized RNFL defects that were difficult to detect with OCT consisted of those cases that were almost less than 20degrees. The limitations of the OCT scan itself in patients with RNFL with an angular width defect less than 10degrees and the problems of RNFL thickness analysis processing in patients with an angular width of 11 to 30degrees may decrease the sensitivity of OCT in diagnosing RNFL defects.

Keyword

Optical coherence tomography; RNFL defect; RNFL fundus photograph

MeSH Terms

Eye
Humans
Nerve Fibers
Retinaldehyde
Tomography, Optical Coherence
Retinaldehyde

Figure

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  Figure 1. False negative findings of OCT and measurement of the location and width of RNFL defect on red-free fundus photograph. Localized, wedge-shaped RNFL defect was identified on red-free fundus photograph (A, arrows). But RNFL thickness throughout 360° (12 zones) were measured normally on RNFL thickness average analysis of OCT (B). The diameter and the location of the circle were determined as they corresponded as closely as possible to the circle displayed in the fundus image of RNFL thickness report. A reference line was drawn horizontally through the center of the circle. The temporal meeting point of the line with the circle was set at 0°. The directional angle was assessed in a clockwise direction for right eyes and a counterclockwise direction for left eyes. The start (S) and end (E) points of each RNFL defect, where the borders of the defect met with the circle, were determined (A).

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  Figure 2. Analysis of causes about false negative response of OCT. (A) Localized RNFL defect was detected on red-free fundus photograph. The start (S) and end (E) points of RNFL defect were assessed as angular measure from 0° on reference line. The measured values were then converted to linear measures by multiplying by the result by D in millimeter and dividing 360°. (B) RNFL defects were identified in topographically matched region as a deflection on OCT scan image of RNFL thickness report (arrow). (C) RNFL defects were not indentified in topographically matched region on OCT analysis image of RNFL thickness report (arrow), which display the results of measuring the RNFL thickness as two white lines through automated computer algorithm, so-called “layer on”.

• 

  Figure 3. Analysis of causes about false negativeness of OCT. (A) Two localized RNFL defects were detected on red-free fundus photograph. The start (S1, S2) and end (E1, E2) points of RNFL defect were assessed as angular measure from 0° on the reference line. The measured values were then converted to linear measures by multiplying by the result by D in millimeter and dividing 360°. (B) RNFL defects were not already identified in topographically matched region as a deflection on OCT scan image of RNFL thickness report (arrow). (C) RNFL defects were not also indentified in topographically matched region on OCT analysis image of RNFL thickness report (arrow).

Reference

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