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Mary K Durbin, Gary Lee, Sophia Yu, Ian P Conner, Robert T Chang, Tin Aung, Thomas Callan; Intervisit repeatability of a combined retinal ganglion cell index in glaucoma. Invest. Ophthalmol. Vis. Sci. 2020;61(9):PB00106.
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Glaucoma, which involves loss of retinal ganglion cells (RGC), is commonly assessed from structural changes detected by optical coherence tomography (OCT) and functional changes detected by standard automated perimetry. A structure-function RGC index (RGCI) was proposed giving a combined model to stage and to monitor glaucomatous progression, as compared to isolated structural or functional metrics [Medeiros et al. AJO 2012; 154(5)]. In this clinical study, we investigated the intervisit test-retest repeatability of the RGCI.
Visual field (VF) and OCT data were acquired from 74 eyes of 74 glaucoma subjects at 5 repeat visits within 3 months, using HFA™ II-i (ZEISS, Dublin, CA) and CIRRUS™ HD-OCT (ZEISS, Dublin, CA). At each visit, SITA Standard 24-2 VFs and Optic Disc 200x200 and Macula 200x200 cube scans were acquired. Only reliable fields and good quality OCT scans were included.VF thresholds, mean deviation (MD), VF Index (VFI), 16 OCT summary parameters (rim area, cup-to-disc area ratio (CDR), vertical cup-to-disc diameter ratio (vCDR), average and four quadrant RNFL thicknesses, average, minimum, and six sectoral GCIPL thicknesses) were extracted for comparison and to calculate the RGCIs as previously described by Medeiros et al.Intervisit test-retest standard deviation (TRT-SD) and coefficient of variation (CV) were calculated for all parameters together and after dividing subjects into quartiles by their mean MD across qualified visits.
Mean age was 63.6 (SD: 10.1; range: 35.7 to 79.6) years. Mean MD was -3.9 (SD: 4.1; range: -18.2 to 1.2) dB. TRT-SD for RGCI was 0.36 [1e5 count and CV was 5.6% (See Table 1). CVs for the other summary VF and OCT parameters ranged from 1.8 to 7.2%. TRT-SD was similar across the quantiles, ranging from 0.30 to 0.41 [1e5 count] with decreasing MD (See Fig. 1).
The combined RGC index shows reasonable repeatability, within the range of individual OCT and VF summary parameters, in a glaucoma population, including similar repeatability over the range of disease. As such, the RGCI may be a reasonable parameter for use in staging and monitoring glaucoma, especially for both event-based and trend-based progression analyses.
This is a 2020 Imaging in the Eye Conference abstract.
Table 1: Summary TRT-SD and CV of VF, OCT, and RGCI parameters
Figure 1: TRT-SD (with 95% confidence interval) for the MD-grouped quartiles
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