Saccadic movements assessment in eccentric fixation: A study in patients with Stargardt disease

Purpose: To investigate saccadic movements in subjects with eccentric fixation due to a deep central scotoma in Stargardt disease (STGD). Methods: We studied 10 patients with STGD and 10 healthy subjects (control group). Saccadic movements of all the 20 subjects were assessed by using the eye tracker technique Tobii Glasses Pro 2. Standard measurements of reading ability (MNREAD charts), visual acuity (ETDRS charts), contrast sensitivity (Pelli-Robson charts), reading contrast threshold and speed (REX charts), retinal sensitivity and stability and localization of the fixation (MP1 fundus perimetry) were obtained in all subjects. Results: The saccadic movements time was significantly slower in STGD than in healthy subjects (699 +/- 193 ms vs 299 +/- 40 ms,p < 0.001). When STGD patients moved fixation to the target localized in retinal scotomatous areas, the movement was significantly slower compared to non scotomatous areas in the retina (1103 +/- 798 ms vs 524 +/- 187 ms,p = 0.039). There was a trend toward a correlation between slow saccadic movements in STGD subjects and the reading performance indices, although statistical significance was not achieved. Conclusion: Ocular saccades guided by eccentric fixation in STGD patients are significantly slower than in the control group, especially when the target corresponds to retinal areas with a deep scotoma. These results can explain the worse reading performance in STGD subjects, in particular when a non-viewing area on the right part of the text is present.