Evidence for alterations in fixational eye movements in glaucoma

Background: Fixation changes in glaucoma are generally overlooked, as they are not strikingly evident as in macular diseases. Fundus perimetry might give additional insights into this aspect, along with traditional perimetric measures. In this work we propose a novel method to quantify glaucomatous changes in fixation features as detected by fundus perimetry and relate them to the extent of glaucomatous damage. Methods: We retrospectively analysed fixation data from 320 people (200 normal subjects and 120 with glaucoma) from the Preferred Retinal Locus (PRL) detection of a Compass perimeter. Fixation stability was measured as Bivariate Contour Ellipse Area (BCEA), and using two novel metrics: (1) Mean Euclidean Distance (MED) from the Preferred Retinal Locus, and (2) Sequential Euclidean Distance (SED) of sequential fixation locations. These measures were designed to capture the spread of fixation points, and the frequency of position changes during fixation, respectively. Results: In the age corrected analysis, SED was significantly greater in glaucomatous subjects than controls (P = 0.002), but there was no difference in BCEA (P = 0.15) or MED (P = 0.054). Similarly, SED showed a significant association with Mean Deviation (P < 0.001), but neither BCEA nor MED were significantly correlated (P > 0.14 for both). Conclusion: Changes in the scanning pattern detected by SED are better than traditional measures of fixation spread (BCEA) for describing the changes in fixation stability observed in glaucoma.