Abstract
Purpose :
To analyze fixation patterns in 10 glaucoma patients involved in a test-retest study, testing a possible association between perifoveal retinal ganglion cell (RGC) loss and fixation.
Methods :
Thanks to its eye tracking technology, the Compass fundus perimeter (CMP, Centervue, Italy) is able to record fixation (ie x-y retinal movements) during visual field testing with a 25 Hz sampling. The data are then reported as displacements of the Preferred Retinal Locus (PRL). For all subjects, we acquired dense Spectral Domain (SD) OCT vertical scans of the posterior pole (Spectralis SD-OCT, Heidelberg Engineering) with 60 μm spacing and segmented the RGC layer to obtain a RGC thickness map. We matched the detailed confocal fundus images provided by both instruments and remapped the fixation data on the RGC map.
Then, we used the Drasdo model to map the PRL locations to the coordinates of their corresponding RGCs. To test if the local RGC thickness could influence fixation, we divided the RGC map in 36 sectors centered on the fovea, counted the number of times the Drasdo shifted fixation points fell into each sector and correlated it to sector mean RGC thickness. We used random effects in the frame of generalized mixed models to account for correlations among clustered data.
Results :
The subjects had an overall mean sensitivity of 13.1 ± 6.9 dB. 9 patients out of 10 had at least one visual field point depressed within 10° from the fovea and significant perifoveal ganglion cell loss.
Using a generalized linear mixed effect model with a Poisson error distribution we found a significant correlation between sector point counts and RGC absolute thickness (28% increase/μm, p = 0.0003). A significant correlation was also found with the normalized RGC thickness (p = 0.0004).
We then calculated the mean fovea centered vector orientation (in degrees) of the fixation points in each test and found a strong test-retest correlation of the mean fixation orientation within the same subject (correlation coefficient 0.78, p = 0.006).
Conclusions :
The strong association between glaucoma perifoveal RGC loss and fixation orientation suggests that RGC loss may shape fixation patterns. Therefore, high quality imaging, PRL detection and fundus tracking might be useful for accurate visual field testing and precise structure function analysis, especially in advanced glaucoma patients.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.