Early glaucomatous damage is missed by standard metrics of the 24-2 visual field test and OCT circumpapillary retinal nerve fiber layer thickness analysis

Abstract

Purpose : In addition to an optic disc exam, glaucoma diagnosis is often based upon standard metrics of the 24-2 visual field (VF) and circumpapillary retinal nerve fiber layer (cpRNFL) thickness analysis of optical coherence tomography (OCT) scans. We evaluated the sensitivity of these metrics in eyes with mild, but confirmed, damage.

Methods : 143 eyes of 143 patients with abnormal or suspicious discs had open angles, a 24-2 VF mean deviation better than -6dB, and spherical refractive error between +/-6D. Two glaucoma specialists classified eyes as glaucomatous, normal/suspects, or undecided using 24-2 VFs, 10-2 VFs, disc stereo-photos, a custom inner retina reports [1] consisting of 24-2 and 10-2 VF probabilities superimposed on OCT disc and macular probability plots (3D-OCT 2000, Topcon, Inc), as well as information from the patients' charts. Of the 143 eyes, 73 eyes were classified as glaucomatous, 56 eyes as normal/suspects, and 4 eyes as undecided. 53 healthy eyes of 53 individuals were also studied. The 24-2VF and OCT metrics were obtained from commercially available reports. For the 24-2 VF, the metrics were: a mean deviation (MD) with p <5%; a pattern standard deviation (PSD) with p <5%; a glaucoma hemifield test (GHT) outside normal limits; and a cluster criterion (CC) of 3 adjacent points at 5, 5, and 1% or 5, 2, and 2% or worse within a hemifield. For the OCT cpRNFL analysis, the metrics were: a temporal, inferior, or superior quadrant (Q) with p ≤5%; the associated clock hours (CH) with 2 contiguous sectors at p ≤5% or one at p ≤1%; or a mean RNFL thickness (T) less than 75.3 μm or 85.0 μm.[2]

Results : The tables contain the results. For the 73 eyes with confirmed damage, the number of eyes missed/sensitivity for the 24-2 VF ranged from 13 eyes/82% (CC) to 32 eyes/56% (MD) eyes and for the OCT from 15 eyes/79% (Q) to 42/42% (T:75.3 um). While combining metrics slightly improved sensitivity, this was minimally effective, and specificity declined (see Tables). Further, 11 eyes were missed by all 4 24-2 VF metrics and 14 eyes by all 4 OCT metrics. 11 of these were local defects clearly seen on 10-2 and/or macular scans probability plots.

Conclusions : Confirmed glaucomatous damage can be missed by standard 24-2 VF and OCT metrics. 1. Hood & Raza. BJO. 2014; 2. Wollstein et al. BJO. 2012.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

 

Table1: 24-2VF

 

Table 2: OCT