Cognitive regulation of saccadic velocity by reward prospect.

It is known that expectation of reward speeds up saccades. Past studies have also shown the presence of a saccadic velocity bias in the orbit, resulting from a biomechanical regulation over varying eccentricities. Nevertheless, whether and how reward expectation interacts with the biomechanical regulation of saccadic velocities over varying eccentricities remains unknown. We addressed this question by conducting a visually guided double-step saccade task. The role of reward expectation was tested in monkeys performing two consecutive horizontal saccades, one associated with reward prospect and the other not. To adequately assess saccadic velocity and avoid adaptation, we systematically varied initial eye positions, saccadic directions and amplitudes. Our results confirmed the existence of a velocity bias in the orbit, i.e., saccadic peak velocity decreased linearly as the initial eye position deviated in the direction of the saccade. The slope of this bias increased as saccadic amplitudes increased. Nevertheless, reward prospect facilitated velocity to a greater extent for saccades away from than for saccades toward the orbital centre, rendering an overall reduction in the velocity bias. The rate (slope) and magnitude (intercept) of reward modulation over this velocity bias were linearly correlated with amplitudes, similar to the amplitude-modulated velocity bias without reward prospect, which presumably resulted from a biomechanical regulation. Small-amplitude (≤ 5°) saccades received little modulation. These findings together suggest that reward expectation modulated saccadic velocity not as an additive signal but as a facilitating mechanism that interacted with the biomechanical regulation.

Outcomes and complications of hydrogel scleral explant removal.

BACKGROUND AND OBJECTIVE: To report symptoms of extrusion of hydrogel explants after retinal detachment (RD) repair and the outcomes and complications following removal. PATIENTS AND METHODS: All 23 patients had previous RD repair by episcleral buckle with hydrogel explant. Signs and symptoms of scleral buckle (SB) extrusion were analyzed. Main outcomes measured were redetachment of the retina, persistent diplopia, and decreased postoperative visual acuity (VA). RESULTS: Mean time between RD repair and removal of extruded SB was 16.2 years (range: 11 to 21 years). Fifteen patients (65%) received encircling SB and 8 had segmental SB. SB was combined with vitrectomy in 12 patients and 3 received silicone oil. Common complaints included limited ocular motility, presence of a palpable mass under the eyelid, pain and discomfort, diplopia, visible SB under eroded conjunctiva, complete immobility, and signs of infection. Two eyes were phthisical. No scleral perforations occurred during removal of explants. After SB removal, RD recurred in 2 patients and diplopia persisted in 4. VA was not affected by SB removal. CONCLUSION: Deterioration may occur after implantation for 10 years or longer. This is due to microstructural change of the hydrogel material. The most common problems are motility disturbance and presence of a tumor-like, palpable mass under the eyelid. Removal of the implant can alleviate some ocular problems. However, RD can recur and diplopia may persist after removal of the SB. Vision usually is not affected.