Changes in Saccadic Velocity Across the Human Lifespan

Abstract

Abstract: : Purpose: To determine the variation of saccadic peak velocity as a function of age. Methods: A total of 135 normal subjects participated in the study, ranging in age from 3 to 86 years. Eye movements were recorded using a video based eye tracker sampling at 120Hz (ELMAR 2020). Subjects made visually guided prosaccades responding to dot stimuli (white dot on black back ground) presented randomly and of varying amplitude ranging from 5 to 30 degrees horizontally in both leftward and rightward directions. Eye position data were differentiated to obtain velocity. Saccades were determined using a velocity threshold method. Saccadic amplitude [A] was plotted against peak velocity [V_p] (main sequence) and fitted with the exponential function (V_p=V_pmax [1-exp (KA)]) in accordance with previous literature. The asymptotic peak velocity [V_pmax] and the slopes at origin [K] were calculated for all subjects. Subjects were categorized into groups (3year old ,4,5,6,7-9,10-19,20-29 till 80-86). A one-way ANOVA was performed on the categorized age groups. Post hoc Bonferroni comparisons were employed to the results of the ANOVA. Results: Low saccadic peak velocities were seen in very young children and the highest were seen in the adolescent group. Generally, an increasing trend in asymptotic peak velocity was seen up to age 20 followed by a decrease until 50 years where it remained stable until it decreased in the ninth decade. The asymptotic peak velocity elicited in response to the stimulus varied significantly between age groups (F_{1, 135} = 7.323; p=0.000). Post hoc tests indicated a significant difference (p<0.05) between adolescent children (age group between 10 to 19) and other age groups except, 6, 7-9,20-29,50-59,70-79 age groups. K values followed a similar trend with respect to age as the asymptotic peak velocities. A significant difference was seen for K values between age groups (F_{1, 135} =6.128; p=0.000). Conclusions: Age was found to be a significant parameter in predicting asymptotic peak velocity. It is therefore important to compare test data (scientific or clinical) to age matched normals since there are significant changes in saccadic peak velocity across the human life span (3-86 years).

Keywords: eye movements: saccades and pursuits • visual development • aging: visual performance