Optical coherence tomography (OCT) can be used to understand and follow advanced glaucoma

Abstract

Purpose : It is commonly assumed that optical coherence tomography (OCT) cannot be used for following eyes with advanced glaucoma [e.g., eyes with 24-2 visual field (VF) with mean deviation (MD) ≤ -15 dB]. While this may be true for OCT metrics such as average thickness of the circumpapillary retinal nerve fiber layer (cpRNFL),[1] we hypothesize that inspection of OCT circle scans allows one to both understand and follow glaucomatous damage in eyes with advanced glaucoma.[2]

Methods : Forty-one eyes from 35 patients (mean: 67.5 ± 13.5, range: 22.1 to 89.4 yrs) with glaucoma had a 24-2 MD ≤ -15 dB (mean: -19.89 ± 4.07, range: -31.67 to -15.01 dB). All eyes had averaged circle scans (Spectralis, Heidelberg Engr). To examine the relationship between structural and functional metrics, the R² value was calculated between the 24-2 MD and global thickness. In addition, each circle scan was inspected, and preserved cpRNFL regions in the temporal half of the disc marked. These regions were topographically compared to 10-2 VF locations using a schematic model in Fig. 1.[2]

Results : Global cpRNFL thickness varied between 28 and 64 um (47.8 ± 9.56) and was poorly correlated with 24-2 MD (R²=0.06), as expected.[1] On the other hand, for 36 of the 41 eyes, there were preserved portions of the cpRNFL clearly visible on the circle scan (e.g., within green rectangle in Fig. 2A, enlarged in 2B). In all cases, these regions of preserved cpRNFL topographically agreed with the preserved regions on 10-2. For example, the region within the green rectangle in Fig. 2A,B is shown as the green arc in Fig. 2C. This disc region is associated with the retinal and 10-2 regions shown in pale green in Fig. 2C,D. In 4 of the 5 remaining eyes, there was evidence of RGC layers on macular B-scans, which could also be topographically compared to VFs.

Conclusions : OCT scans can be used to assess the preserved regions of cpRNFL in eyes with advanced glaucoma. There is excellent topographical agreement among preserved regions on the 10-2 VF and the cpRNFL. On the other hand, metrics such as VF MD and OCT average thickness are poor ways to identify preserved regions of vision. Instead, qualitative assessment of OCT scans should be incorporated to follow changes in eyes with advanced glaucoma.

1. Medeiros et al., AO, 2012; 2. Hood, PRER, 2017.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

Fig. 1. Schematic model of the macula (± 8°) with 10-2 VF points.

 

Fig. 2