Background: Reading disability is the main problem in patients with hemianopic field defects (HFD). The purpose of this study was to examine eye movement patterns in HFD with special emphasis on the importance of clinical parameters.
Methods: 40 patients with HFD (21 left, 19 right) and 21 normal subjects were examined by an infrared reflection system to record eye movements during reading and by Tübingen perimetry. Reading and clinical parameters were correlated.
Results: Reading speed was reduced in all patients compared to normal subjects (853 vs 1541 characters/min), in right (785 char/min) more than in left HFD (915 char/ min). The number of saccades and regressions per line was markedly increased in right HFD (9.8 vs 4.5; 2.2 vs 0.3), less so in left HFD (6.4; 1.0). The number of saccades during the return sweep was more increased in left HFD (1.5 vs 0.5) than in right HFD (0.9). Reading parameters improve with increasing distance of HFD to the visual field center (minimum in right HFD 5 degrees, in left HFD 2 degrees) and with increasing time since onset. Some left HFD patients learn a predictive strategy for the return sweep. The effect is less pronounced for age and skill and is absent for the localization of the lesion.
Conclusion: Patients with right HFD are more disabled. The side of the HFD, its distance to the visual field center and the time since onset are significant parameters for reading performance. The analysis of reading parameters in correlation with clinical parameters provides valuable information about the necessary perceptual field and learning effects and is helpful in rehabilitation.