Fixation stability in normal children

Abstract

Abstract: : Purpose: To investigate the fixation stability in normal Swedish children. Methods: One hundred and two normal children in four age groups (4–6, 7–9, 10–12 and 13–15y) underwent infrared reflexion eye movement recordings (IOTA Inc. Sweden) while fixating a small high contrast target on a computer screen 50 cm in front of the face. The children used a chin rest for stabilisation of the head during the recording and instructed to keep a steady fixation on the target. After a three–point calibration had been performed, the fixational eye movements were recorded for 30 seconds. By inspecting the whole recorded file off–line the most stable ten seconds of each recording were chosen for analyses with regard to number of blinks, intruding saccades and fixation stability. The fixation stability was calculated as the area radius containing 67% of the fixation positions (AR) after the blinks and intruding saccades with an amplitude larger than 3 degrees had been manually taken away from the recording. Also the distribution of the horisontal and vertical fixational position around the center of gravity of fixation (CG) as well as the horisontal and vertical vergence position were calculated. Results: There was no significant difference between the groups with regard to number of blinks during fixation. However, the number of intruding saccades decreased with increasing age (p=0.001). Also the AR decreased with increasing age (p<0.001). The AR for the four age groups were 5.7, 3.1, 2.2 and 1.7 degs. respectively. The mean horisontal (p=0.001) and vertical (p<0.001) fixational position from the CG was found to decrease with increasing age. The horisontal (p=0.003) and the vertical (p=0.003) vergence position was also found to decrease with increasing age. No significant preponderance of directional location of the fixation positions around the CG was found. Conclusions: Fixational stability increase with increasing age in normal children. The results will serve as a normal material for studying fixational behaviour in different pediatric patient groups.

Keywords: eye movements • infant vision • strabismus