The Location of Peripapillary Glaucomatous Defects Seen on Frequency-Domain OCT Scans

Abstract

 

Purpose

 

To examine the locations of glaucomatous damage in the peripapillary retinal nerve fiber layer (RNFL), thickness measurements from frequency domain optical coherence tomography (fdOCT) disc scans were analyzed.

 

Methods

 

Optic disc fdOCT volume scans from 54 healthy control eyes and 130 patient eyes, classified as suspect or mild glaucoma, were analyzed. All patient eyes had 24-2 visual fields (VFs) with mean deviations better than -5.5 dB. By hand-correcting automated segmentation [1,2], the RNFL thickness profile was obtained for a peripapillary circle 1.73mm in radius. RNFL defects were defined as peripapillary regions where the patient's RNFL thickness fell below the 99% confidence limit of control values. The location of a defect in each eye was defined as the point of greatest difference between the patient's and control's RNFL thickness values. The locations of major blood vessels (BVs) were also marked. The BVs were separated into superior-nasal (SN), superior-temporal (ST), inferior-temporal (IT), and inferior-nasal (IN) groups and their locations averaged.

 

Results

 

Of the 130 patient eyes, 55 exhibited RNFL defects. The locations of these defects (figure) showed a bimodal distribution in the superior disc, while the locations in the inferior disc showed a single peak. Average BV locations are indicated by the red lines. Defects clustered around the ST, SN, and IT, but not the IN BVs. As expected, the greatest RNFL thickness in controls (green in fig.) was associated with the average locations of the 4 major BV clusters. However, control RNFL thickness was not a perfect predictor for defect location.

 

Conclusions

 

The glaucomatous defects in the peripapillary RNFL fall into three regions, two in the superior disc and one in the inferior disc. For the ST, SN and IT region, the locations of the defects are associated both with the major BVs and the regions of thickest RNFL in healthy controls. However, the absence of defects in the IN region indicates that the locations of defects are not simply related to either BV location or RNFL thickness. 1. Raza et al. AO, 2011; 2. Yang et al. Opt Exp, 2011

 

 

Figure 1. Blue bars: frequency of RNFL defects as a function of location around disc (10° bins). Green region: the mean control thickness scaled to the maximum mean control thickness of 148.9 µm (green circle). Red lines: the locations of the SN, ST, IT, and IN BVs.

 

Keywords: 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • 627 optic disc • 610 nerve fiber layer