PurposeTo evaluate the contribution of fixational saccades toward fixation instability in strabismic monkeys.MethodsBinocular eye movements were measured as six experimental monkeys (five strabismic monkeys and one monkey with downbeat nystagmus) and one normal monkey fixated targets of two shapes (Optotype, Disk) and two sizes (0.5°, 2°) during monocular and binocular viewing. Fixational saccades were detected using an unsupervised clustering algorithm.ResultsWhen compared with the normal monkey, amplitude and frequency of fixational saccades in both the viewing and nonviewing eye were greater in 3 of 5 strabismic monkeys (1-way ANOVA on ranks P < 0.001; median amplitude in the normal monkey viewing eye: 0.33°; experimental animals: median amplitude range 0.20–0.82°; median frequency in the normal monkey: 1.35/s; experimental animals: median frequency range 1.3–3.7/s). Increase in frequency of fixational saccades was largely due to quick phases of ongoing nystagmus. Fixational saccade amplitude was increased significantly (3-way ANOVA; P < 0.001) but by small magnitude depending on target shape and size (mean difference between disk and optotype targets = 0.02°; mean difference between 2° and 0.5° targets = 0.1°). Relationship between saccade amplitude and the Bivariate Contour Ellipse Area (BCEA) was nonlinear, showing saturation of saccade amplitude. Fixation instability in depth was significantly greater in strabismic monkeys (vergence BCEA: 0.63 deg2–2.15 deg2) compared with the normal animal (vergence BCEA: 0.15 deg2; P < 0.001).ConclusionsIncreased fixational instability in strabismic monkeys is only partially due to increased amplitude and more frequent fixational saccades. Target parameter effects on fixational saccades are similar to previous findings of target effects on BCEA.

Purpose Recent magnetic resonance imaging studies have suggested that extraocular muscles (EOM) are further divided into transverse compartments that behave differentially and often unexpectedly during eye movements. Selective innervation of EOM compartments may explain the observation that certain horizontal recti compartments contribute to specific vertical eye movements and that some cyclovertical EOM compartments do not contribute to vertical vergence. We investigated the discharge characteristics of extraocular motoneurons during these eye movement tasks where EOM compartments behaved differentially for evidence of selective innervation. Methods We recorded from all six extraocular motoneuron populations in the abducens, oculomotor, and trochlear nuclei as two non-human primates performed vertical vergence and vertical smooth-pursuit. The relationship between motoneuron firing rate, horizontal and vertical eye parameters of the innervated eye during each task was determined using multiple linear regression. Results All 26 medial rectus motoneurons recorded showed no significant modulation during vertical smooth-pursuit and vertical vergence. Twenty-eight of 30 abducens motoneurons showed no significant modulation during vertical vergence, and all 30 cells did not modulate during vertical smooth-pursuit. For the cyclovertical motoneurons, 147 of the 149 cells (44/46 inferior rectus, 27/27 superior oblique, 41/41 superior rectus and 35/35 inferior oblique) modulated significantly during vertical vergence. Conclusions Extraocular motoneuron activity during vertical vergence and vertical smooth-pursuit does not support the theory that EOM compartments are selectively innervated. The observed differential behavior of EOM compartments is likely not driven by oculomotor control and could be due to passive change in EOM cross-sectional area.

ABSTRACT:Our aim was to evaluate the influence of visual impairment on the quality of life of patients reporting at the low vision centre of the Eastern Regional Hospital in Koforidua. The World Health Organization Quality Of Life (WHOQOL-Bref) which assesses quality of life in four main domains was administered to two hundred and ninety four (294) patients who visited the low vision centre of the Eastern Regional Hospital, for various eye services. Additional information on patient demographics and their visual acuities were obtained. The mean quality of life scores were determined for the visually and non-visually impaired. 86(29.3%) of the participants were visually impaired (presenting vision worse than 6/18). A significant difference in mean age was realized between subjects who were visually impaired (53.7 ± 18.4) (mean ± SD) and subjects who were not visually impaired (34.3 ± 13.1) (p = 0.001). The visually impaired participants had a lower quality of life scores in all four domains of quality of life naming, environmental, physical, social and psychological with 7.5% unadjusted reduction in overall quality of life.Visual impairment is associated with significant reduction in different quality of life domains for this population. Quality of life is poorer with increasing severity of visual impairment.

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