Comparison of retinal ganglion cell indices determined from different SITA threshold strategies

Abstract

Purpose : Glaucomatous disease, ultimately related to the loss of retinal ganglion cells (RGC), is most commonly assessed from the structural changes detected by optical coherence tomography (OCT) and functional changes detected by standard automated perimetry. Medeiros et al. (AJO. 2012; 154:814-824) proposed a structure-function RGC index (RGCI) using SITA Standard (SS) visual fields (VF), giving a combined model to monitor glaucoma's progression, as compared to isolated structural or functional metrics. We investigated differences in the RGCI when estimated from 3 types of SITA VFs in glaucomatous eyes.

Methods : 24-2 SS, SITA Fast (SF), and SITA Faster (SFR) VF and spectral domain OCT were acquired from 100 eyes of 100 glaucoma patients at 2 repeat visits within 1 month, using HFA3 (ZEISS, Dublin, CA) and CIRRUS™ HD-OCT (ZEISS, Dublin, CA). Using Medeiros’ previously described method, RGCIs were calculated using the 3 SITA VFs and the same OCT data between visits. Significance testing (2 one-sided, paired t-tests, ∝ = 0.05) for inter-strategy equivalence versus RGCI_SS was performed with Visit 2 data, using limits of equivalence of ± 5% from the reference RGCI_SS mean. Intra-strategy equivalence for RGCI_SS was similarly tested using data from both visits. Test-retest standard deviation (TRT-SD) and coefficient of variation (CV) were calculated for repeatability.

Results : Mean age was 67.1 ± 10.9 years (range: 26.9 to 82.7 years). Table 1 shows the mean ± SD for the OCT average retinal nerve fiber (RNFL) thickness, VF Mean Deviations (MD), and RGCIs. Bland-Altman and scatter plots (Fig. 1) show good agreements and strong correlations (comparable limits of agreement with Pearson’s r> 0.98) for all comparisons. RGCI_SF and RGCI_SFR were statistically equivalent to RGCI_SS (P < 0.001 and P < 0.001, respectively). TRT-SD and CV of RGCI_SF and RGCI_SFR were no worse than the values for RGCI_SS, indicating comparable variabilities, which were also larger in magnitude than inter-strategy differences.

Conclusions : RGCIs calculated from OCT and the various types of SITA VFs produced comparable values in a wide range of glaucomatous eyes and, therefore, could be compatible in mixed analyses. TRT variabilities were comparable among all index versions.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

Table 1. Mean ± SD of Summary Parameters & Repeatability Metrics

 

Figure 1. Intra-Strategy (Top) & Inter-Strategy (Middle, Bottom) Scatter & Bland-Altman comparisons of RGCIs