Saccadic reaction times in alternating cover.

PURPOSE: The aim of this study was to compare saccadic reaction times (SRTs) during the alternating cover with SRTs during monocular viewing. METHODS: Seven subjects with intermittent exotropia, eight subjects with esophoria and ten control subjects were participated. The normal-task was to fixate the central fixation point until the peripheral target appeared randomly either 5 degrees to the right or left. In the alternating cover task (AC-task), the cover was switched from the fixating eye to the other eye, central fixation target was simultaneously extinguished and peripheral target was lit. An infrared limbal-tracking system and electro-oculogram were used for measurements of eye movements. The study followed the tenets of the Declaration of Helsinki. We certify that there is no conflict of interest. RESULTS: In AC-task, the average SRTs of control subjects, subjects with exophoria and subjects with intermittent exotropia were 224.2 ± 46.5 ms, 198.2 ± 45.3 ms and 227.3 ± 69.9 ms, respectively. On the other hand, the average SRTs of control subjects, subjects with exophoria and subjects with intermittent exotropia in normal-task were 200.7 ± 37.8 ms, 178.2 ± 34.6 ms and 185.4 ± 54.1 ms, respectively. CONCLUSIONS: The SRTs of most control subjects, subjects with exophoria and subjects with intermittent exotropia in AC-task were prolonged compared to normal-task.

Smooth-pursuit eye-movement-related neuronal activity in macaque nucleus reticularis tegmenti pontis.

Neuronal responses that were observed during smooth-pursuit eye movements were recorded from cells in rostral portions of the nucleus reticularis tegmenti pontis (rNRTP). The responses were categorized as smooth-pursuit eye velocity (78%) or eye acceleration (22%). A separate population of rNRTP cells encoded static eye position. The sensitivity to pursuit eye velocity averaged 0.81 spikes/s per degrees /s, whereas the average sensitivity to pursuit eye acceleration was 0.20 spikes/s per degrees /s(2). Of the eye-velocity cells with horizontal preferences for pursuit responses, 56% were optimally responsive to contraversive smooth-pursuit eye movements and 44% preferred ipsiversive pursuit. For cells with vertical pursuit preferences, 61% preferred upward pursuit and 39% preferred downward pursuit. The direction selectivity was broad with 50% of the maximal response amplitude observed for directions of smooth pursuit up to +/-85 degrees away from the optimal direction. The activities of some rNRTP cells were linearly related to eye position with an average sensitivity of 2.1 spikes/s per deg. In some cells, the magnitude of the response during smooth-pursuit eye movements was affected by the position of the eyes even though these cells did not encode eye position. On average, pursuit centered to one side of screen center elicited a response that was 73% of the response amplitude obtained with tracking centered at screen center. For pursuit centered on the opposite side, the average response was 127% of the response obtained at screen center. The results provide a neuronal rationale for the slow, pursuit-like eye movements evoked with rNRTP microstimulation and for the deficits in smooth-pursuit eye movements observed with ibotenic acid injection into rNRTP. More globally, the results support the notion of a frontal and supplementary eye field-rNRTP-cerebellum pathway involved with controlling smooth-pursuit eye movements.

[Reflexive and voluntary saccades in Parkinson's disease].

PURPOSE: To evaluate the characteristics of saccadic eye movements in patients with Parkinson's disease(PD). SUBJECTS AND METHODS: Eye movements of 14 patients with moderate to advanced PD and 12 age-matched controls were recorded with an infrared system. Two kinds of saccade tasks were used: saccade tasks for eliciting reflexive saccades(visually guided saccades in the gap condition) and saccade tasks for eliciting volitional saccades(visually guided saccades, saccades in overlap condition, memory-guided saccades, and anti-saccades). Latency, accuracy, peak velocity, and other parameters of saccades were evaluated. RESULTS: Visually guided saccades and saccades in the gap condition were slightly hypometric in PD patients. Saccades in the short-term overlap condition were not impaired in PD patients. Increased mean latencies and decreased degrees of accuracy of memory-guided saccades, and increased error rates of the memory-guided saccade task were marked in PD patients. Error rates in the anti-saccade task were not increased in PD but the mean saccadic latencies were slightly increased. CONCLUSION: Reflexive saccades are preserved in PD, whereas memory-guided saccades are markedly impaired. But anti-saccades in a task for eliciting in volitional saccades are not impaired in PD.