Slowed Saccadic Reaction Times in Seemingly Normal Parts of Glaucomatous Visual Fields

Abstract

Purpose: In eye movement perimetry, peripheral stimuli are confirmed by goal-directed eye movements toward the stimulus. The saccadic reaction time (SRT) is regarded as an index of visual field responsiveness, whereas in standard automated perimetry (SAP), the visual field sensitivity is tested. We investigated the relation between visual field sensitivity and responsiveness in corresponding locations of the visual field in healthy controls and in patients with mild, moderate and advanced glaucoma.Materials and Methods: Thirty-four healthy control subjects and 42 glaucoma patients underwent a 54-point protocol in eye movement perimetry (EMP) and a 24-2 SITA standard protocol in a Humphrey Field Analyzer. The visual field points were stratified by total deviation sensitivity loss in SAP into 6 strata. A generalized linear mixed model was applied to determine the influence of the various factors.Results: The generalized linear mixed model showed that the mean SRT increased with increasing glaucoma severity, from 479 ms in the control eyes to 678 ms in the eyes of patients with advanced glaucoma (p < 0.001). Mean SRTs significantly increased with increasing SAP sensitivity loss. Even at the locations where no sensitivity loss was detected by SAP (total deviation values greater or equal than 0 dB), we found lengthened SRTs in mild, moderate and advanced glaucoma compared to healthy controls (p < 0.05) and in moderate and advanced glaucoma compared to mild glaucoma (p < 0.05). At locations with total deviation values between 0 and −3 dB, −3 and −6 dB and −6 and −12 dB, we found similar differences.Conclusions: The lengthened SRT in areas with normal retinal sensitivities in glaucomatous eyes, i.e., planning and execution of saccades to specific locations, precede altered sensory perception as assessed with SAP. Better understanding of altered sensory processing in glaucoma might allow earlier diagnosis of emerging glaucoma.

Eye Movement Abnormalities in Glaucoma Patients: A Review

“…65,67 Thepass et al supported this finding and proposed that saccade latency may serve as a useful marker of glaucoma progression prior to field loss. 75 There was also a longer latency from stimulus presentation to peak saccade velocity in glaucoma patients. 64 A more pronounced increase in latency (compared to controls) occurred with a decrease in luminance which was 67 Najjar et al 66 anti-saccade task (16 glaucoma patients and 16 controls) found an increase in errors during this task, which is known to recruit frontal brain regions and test attention/cognition.…”

“… 67 31 perimetric glaucoma aged 72.3 ± 7.9 ** 23 controls (not age-matched; aged 65.9 ± 5.6) Static peripheral saccade target* Reduced velocities, increased latencies, decreased accuracy in glaucoma, correlated to disease severity Thepass et al 2021. 75 76 POAG and PACG glaucoma eyes: mild n=32 (mean age 66.5, MD −2.5), moderate n= 15 (mean age 67.9, MD −9.6), advanced n=29 (mean age 68.3, MD −17.6) 58 control eyes (mean age 65.5) Eye movement perimetry (54-point) with 24–2 visual field Saccade latency increased (even in areas of preserved visual field) with glaucoma severity which was also correlated to stimulus intensity and eccentricity. Notes : *static Peripheral Stimulus: Participants View a Central Fixation Point, Which is Extinguished After a Randomised Time Period (Within a Range of a Few Seconds) and a Stationary Saccade Target Appears in the Periphery.…”

“…For example, Thepass et al’s larger cohort of 76 glaucomatous eyes was divided into four main subgroups, testing 8 different target eccentricities, which limits their overall effect size. 75 …”

“… 66 Differences in saccade latencies in between-eye experiments (eg comparing one patient’s less-diseased eye to their more-diseased eye) reveal that the magnitude of glaucoma burden is positively correlated to increased latency. 75 Longer saccade latency in glaucoma patients may be caused by eye movement control centres (eg the SC, where 10% of RGCs target 6 ) requiring a longer time to collect visual information from the reduced RGC input (ie reduced signal). It would be of interest to explore reflexive saccades which isolate the retinotectal tract in a group of glaucoma patients, similar to Abe et al’s aim with OKN.…”

“…For example, Thepass et al's larger cohort of 76 glaucomatous eyes was divided into four main subgroups, testing 8 different target eccentricities, which limits their overall effect size. 75 A wide range of eye tracking devices were used and results from each study may not be directly comparable. A potential drawback to the low-cost portable eye tracking technology used in many of these studies is the reduced video frame rate (eg 25-200 Hz) compared to costly and less-portable laboratory devices with higher performance of over 1000 Hz.…”