RANGE OF STRUCTURAL AND FUNCTIONAL ABNORMALITIES IN EYES WITH ADVANCED GLAUCOMATOUS CUPPING

Abstract

Abstract: : Purpose: To evaluate the characteristics of the retinal nerve fiber layer (RNFL) and visual field in eyes with advanced glaucomatous cupping. Methods: Complete examination, standard achromatic perimetry (SAP), scanning laser polarimetry with variable corneal compensation (SLP–VCC) and optical coherence tomography (Stratus OCT) imaging of the peripapillary retina and optic disc were performed. Advanced cupping was defined as vertical cup–disc ratio (VCDR) ≥ 0.80 using OCT optic nerve head (ONH) analysis. Structural and functional characteristics were assessed separately in eyes with disc area <2 mm² and ≥2 mm². Exclusion criteria were visual acuity < 20/40, diseases other than glaucoma, and unreliable SAP. RNFL images using OCT and SLP–VCC were obtained using a circular scan (3.4 and 3.2 mm diameter respectively) centered on the optic disc. ONH images were obtained using 6 radial scans centered on the optic disc. Results: 29 eyes of 29 glaucoma patients with VCDR ≥ 0.80 on OCT ONH analysis were enrolled (mean age 70 ± 12 years, range 40–93). The average visual field mean defect = –18.0 ± 10.2 dB (range –1.1 to –32.8). OCT generated VCDR demonstrated close agreement (R² = 0.60, P = 0.0002) with masked clinical assessment of VCDR. 11 eyes (38%) were excluded from further analysis due to failure of analysis by the OCT software (n = 6, MD = –24.6 to –30.1 dB) and failure of image acquisition by SLP–VCC (n = 5, MD = –22.7 to –30.1 dB). Mean RNFL thickness using OCT was 52.8 ± 14.7µm (range, 24.3 to 76.3) and SLP–VCC was 40.1 ± 8.4µm (range, 24.0 to 52.7); mean rim area using OCT was 0.5 ± 0.1 mm² (range, 0.2 to 0.7). A significant correlation was observed between MD and RNFL thickness using OCT and SLP–VCC (R² = 0.5, P = 0.0009) and rim area (R² = 0.3, P = 0.02). Eyes with disc area <2 mm² demonstrated significantly (P = 0.04) greater visual field loss (MD = –26.0 ± 5.3 dB) and RNFL loss using OCT (36.3 ± 10.5µm) compared with eyes with disc size ≥2mm² (–12.7 ± 10.0 dB; 56.0 ± 13.5µm respectively). Conclusions: Eyes with advanced glaucomatous cupping have a wide range of RNFL and visual field loss, which may be attributed to variability in optic disc size. Eyes with visual field MD ≤ –23 dB have a high failure rate using OCT and SLP–VCC.

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