A comparative study of computerised visual field testing and optic disc morphometric parameters in the follow-up of primary open angle glaucoma.

Abstract

To evaluate the correlation between computerised visual field testing and optic disc morphometric parameters (rim area, rim/disc area ratio, cup/disc area ratio and optic disc surface smoothness (ODSS)) in the follow-up of a group of patients affected by primary open angle glaucoma (POAG). Reliable automated perimetry (Humphrey 640 VFA, central 30-2 threshold program) was performed at T0 (the enrollment time), T1 (after 6 +/- 1 months; range 5-7 months), T2 (12 +/- 1 months), T3 (18 +/- 1 months), and T4 (the end of the follow-up period: 24 +/- 2 months) in one eye randomly chosen from each of 30 POAG patients. Computerised optic disc analysis (IMAGEnet X Rev-3-51b, Topcon Europe, The Netherlands) was performed at T0 and T4. To evaluate the correlation between morphometric parameters and computerised visual field testing, the stability or worsening of visual field test was evaluated by means of 'Mean Deviation linear regression analysis' (STATPAC 2 software); that of morphometric parameters was studied using their coefficients of variation. A rank of '0' was assigned to stability and a rank of '1' to worsening. The Spearman rank correlation coefficient was used to evaluate statistically the correlations between visual field analysis and morphometric parameters. Furthermore kappa statistic was used to evaluate the agreement of morphometric parameter changes with visual field progression analysis. According to the MD slope regression analysis, in 18 patients the visual fields were stable while in 12 they were worsening during the follow-up period. In 86.65% of patients (n = 26) the morphometric parameter ODSS and visual field analysis were concordant (p < 0.0001). In 80% of patients (n = 24) the cup/disc area ratio and visual field analysis were concordant (p < 0.001). The other morphometric parameters (rim area, rim/dics area ratio) were less correlated with visual field analysis than ODSS (p < 0.05). The agreement of visual field analysis with all the morphometric parameters was good (kappa = 0.690, 95% confidence interval (CI) of kappa = 0.589-0.790). The agreement of visual field analysis with ODSS and cup/disc area (kappa = 0.688; 95% CI = 0.511-0.864) was better than the agreement of visual field analysis with rim area and rim/disc area ratio (kappa = 0.438; 95% CI = 0.260-0.655). Analysis of the progression of visual field damage and optic nerve head morphometric parameters should both be taken into account in glaucoma follow-up. Among the morphometric parameters evaluated by means of Topcon IMAGEnet, ODSS and (to a lesser extent) the cup/disc ratio should have the greatest weight.