Prevalence of retinal nerve fiber layer and visual field abnormalities in eyes with pre–perimetric glaucomatous optic neuropathy using advanced imaging and psychophysical testing

Abstract

Abstract: : Purpose: To evaluate the prevalence of retinal nerve fiber layer (RNFL) and visual field abnormalities in eyes with pre–perimetric glaucomatous optic neuropathy (GON) using advanced imaging and psychophysical testing. Methods: Complete examination, standard achromatic perimetry (SAP), short wavelength automated perimetry (SWAP), frequency doubling technology (Humphrey Matrix FDT), scanning laser polarimetry (SLP–VCC) and optical coherence tomography (Stratus OCT) imaging of the peripapillary RNFL were performed. Pre–perimetric GON was defined as either cup/disc asymmetry between fellow eyes of greater than 0.2, rim thinning, notching, excavation, or RNFL defect with normal SAP. Exclusion criteria were visual acuity < 20/40, diseases other than glaucoma, and abnormal or unreliable SAP. Abnormal RNFL measurements using OCT were defined as mean or quadrantic thickness values outside 95% normal limits. Abnormal SLP–VCC measurements were defined as a cluster of ≥ 3 contiguous superpixels outside 95% normal limits with 1 outside 99% normal limits, or any retardation parameter outside 95% normal limits. Abnormal FDT measurements were defined as MD or PSD outside 95% confidence limits and GHT outside normal limits. Abnormal SWAP measurements were defined as MD or PSD outside 95% confidence limits and a cluster of ≥ 3 contiguous points with probability level of <5%, with at least one of them with probability < 1% level in the pattern deviation plot. Results: 25 eyes of 25 patients with pre–perimetric GON were enrolled (mean age 60 ± 15 years, range 28–83). Mean central corneal thickness (CCT) was 563.4 ± 40.2µm, range 498– 626.3. Visual field abnormalities were identified in 6/25 eyes (24%) using SWAP and 5/22 eyes (22%) using FDT. RNFL loss using OCT and SLP–VCC was present in 12/25 (48%) and 15/25 (60%) eyes respectively. CCT was not significantly associated with RNFL loss using OCT or SLP–VCC, or visual field abnormalities using SWAP or FDT (P > 0.05). Mean RNFL thickness and rim area by OCT (80 ± 11.1µm, 0.76 ± 0.15 mm²) and FDT–MD (–2.8 ± 3.6 dB) was significantly worse (P = 0.04, 0.0002, 0.02) in eyes with vertical CDR ≥ 0.6 than eyes with CDR < 0.6 ((90.1 ± 12.3µm, 1.22 ± 0.26 mm², 0.4 ± 2.3 dB, respectively). Conclusions: Diffuse RNFL atrophy was more prevalent than selective visual field loss in this cohort of eyes with pre–perimetric GON. Eyes with greater cupping have a higher likelihood of structural and functional abnormalities.

Keywords: imaging/image analysis: clinical • nerve fiber layer • visual fields