Structure-Function Relationship using Spectral Domain Ocular Coherence Tomography, Flicker Defined Form Perimetry and Standardized Automated Perimetry in Patients with Glaucoma

Abstract

Purpose: : To evaluate the correlation between glaucomatous structural damage and functional defects in patients with glaucoma.

Methods: : The study comprised of 110 participants with mild-moderate glaucoma. Mean age of 63.3 ± 8.8 years (range 45-83), 54% female. Glaucoma was defined according to a modified Hodapp classification into mild (82.2%) or moderate (11.8%) using mean deviation (MD): 2.8 to -10.37 of Humphrey Visual Analyzer (HFA II, Carl Zeiss Meditec). One eye of each participant was randomly assigned if both eyes were eligible for the study (56 OD). The study consisted of 3 visits over a 6 week period and included standard automated perimetry (SAP, 24-2 ASTA-Std; visits 2 and 3) and flicker defined form perimetry (FDF 24-2 ASTAStd; all visits) on the Heidelberg Edge Perimeter (HEP; Heidelberg Engineering (HE)). Digital stereo disc photography and optical coherence tomography (Spectralis HRA+OCT; HE) were acquired at the third visit. The visual fields were divided into sectors corresponding to the six found in the retinal nerve fibre layer (RNFL). The relationship between global and sectoral RNFL thickness with FDF and SAP were analyzed using correlation coefficients and linear regression analysis.

Results: : There was a significant correlation between RNFL thickness to both MD and mean sensitivity (MS) of the visual function (p<0.002; Bonferroni corrected) for the global and sectoral measures, except for the temporal sector for FDF and the temporal, nasal and inferior nasal sectors for SAP. The global measures gave a correlation for MD of r=0.53 (FDF) and r=0.48 (SAP). The highest correlations were found for FDF in the superior and inferior temporal sectors using MD (FDF: r=0.70 & 0.68; SAP: r=0.60 & 0.58 respectively). Although the r-values were similar between FDF and SAP, the structure-function relationships were quite different. The FDF showed a steep linear relationship over the entire range of RNFL thickness while SAP had a flat distribution.

Conclusions: : FDF demonstrated better correlation with SD-OCT than SAP in all sectors of the ONH, in particular in the superior temporal and inferior temporal sectors. SAP showed relatively little abnormality whereas FDF gave a linear reduction over the entire range of RNFL thickness in the superior and inferior temporal sectors.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • perimetry • optic nerve