Eye movements during saccadic and fixation tasks in patients with homonymous hemianopia

The aim of our study was to quantify ocular motor performance in patients with homonymous hemianopia and in healthy controls during saccadic and fixation tasks and to detect potential spontaneous adaptive mechanisms in the hemianopic patients.

Eye movements were recorded in 33 hemianopic patients (15 right, 18 left; disease duration, 0.2-29 years) and 14 healthy subjects by scanning laser ophthalmoscope allowing determination of the absolute fovea position relative to the stimulus without calibration. Landing accuracy of saccades was determined for 5° saccades, indicated by the number of dysmetric saccades (DS), and fixation stability (FS) after landing. In addition, during continuous fixation of a central cross, FS, and distribution of fixational eye movements (FEMs) were measured. Size of macular sparing was determined using custom microperimetry software (stimulus grid, 0.5°).

Compared with controls, landing accuracy was decreased in hemianopic patients, indicated by significantly more DS (hypometric and hypermetric) to the blind side compared with the seeing side. The number of DS was greater in patients with macular sparing of <4°. DS were not correlated with age and disease duration. FS after landing was lower after saccades to the blind side. Distribution of FEM during continuous fixation was asymmetrically shifted to the blind side, especially in cases of macular sparing of <4°.

Number of DS was not correlated with disease duration indicating insufficient spontaneous long-term adaptation. Increased number of DS and decreased FS after landing in patients with small or absent macular sparing stresses the importance of intact parafoveal vision. Asymmetric FEMs during continuous fixation indicate an advantageous adaptive mechanism to shift the visual field border towards the hemianopic side.