Vergence eye movements impairments in schizophrenia and bipolar disorder.

One of the most evaluated eye tracking tasks in schizophrenia (SZ) and bipolar disorder (BD) are smooth pursuit eye movements. They rely on the maintenance of slowly moving object on the fovea. While most of the studies evaluated tracking of a target that moves in the fronto-parallel plane, only two assessed vergence eye movements (VEM), which relies on the pursuit of object that moves in depth. The aim of our study was to compare VEM performance in SZ and BD. We evaluated 28 SZ patients, 32 BD patients and 25 healthy controls (HC). Participants underwent thorough optometric examination before eye tracking task. VEM were measured with the use of infrared eye tracker and dedicated vergence stimuli generator. SZ patients showed higher mean break and recovery points of fusion and shorter correct tracking time than HC. BD individuals revealed tracking accuracy deficits and higher number of saccades than HC. Compared to BD, SZ patients showed decrease of maximal convergence and divergence. Moreover, they presented tracking accuracy deficits of non-dominant eye: altered eyes positioning error during convergence and divergence gain. Exploratory analysis revealed significant gender differences between groups in terms of binocular VEM parameters. In this study we have recognized pattern of eye movement disturbances differentiating abovementioned groups. SZ patients showed decreased vergence tracking range with shorter tracking time and impaired accuracy of non-dominant eye, while BD patients showed higher number of saccades with decreased tracking accuracy. Neuroimaging studies are necessary to identify neuronal underpinnings of VEM impairments in SZ and BD.

Vergence eye movements in bipolar disorder. / Ruchy wergencyjne w chorobie afektywnej dwubiegunowej.

OBJECTIVES: With respect to bipolar disorder (BD), previous research have demonstrated saccadic eye movements abnormalities, manifested mainly as an increase in reaction time (latency) in both prosaccadic and antisaccadic task. So far, there were no studies related to vergence eye movements in subjects with BD. Our primary aim was to evaluate vergence tracking performance in this clinical group. METHODS: 30 patients with BD in remission and 23 healthy controls were enrolled. Subjects underwent optometric examination where near point of convergence was measured by the use of Wolff Wand. Instrumented convergence measurements were performed using infrared eye tracker and dedicated vergence stimuli generator. RESULTS: BD patients presented significantly higher average error between eyes' convergence and convergence required to fixate the target and higher number of saccadic intrusions compared with healthy controls group. Principal component analysis performed on oculometric parameters revealed differences between BD patients and healthy controls. Significant correlations between the vergence disturbances and saccadic intrusions were found. CONCLUSIONS: BD patients showed the alterations of the vergence eye movements similar to the disturbances of eye movements in the fronto-parallel plane. While the abnormalities of vergence eye movements in some mental disorders have been reported, we have for the first time objectively measured this phenomenon in BD.

Gap effect and express saccades generation in amblyopia.

Amblyopia is a neurodevelopmental vision disorder that is associated with abnormal visual stimulation during early childhood. Although our knowledge regarding spatial vision deficits in amblyopic subjects is well established, the neural control of eye movements in amblyopia is yet to be explored. In the present study we have evaluated the gap effect, and for the first time (to our best knowledge), express saccades generation in amblyopic (strabismic as well as anisometropic) and age-matched control subjects. We have compared the saccadic latency under different gap conditions ("no gap," 50 ms gap, and 200 ms gap), between the amblyopic and control groups. Our results have shown that saccadic latency was reduced during the gap paradigms both for amblyopic and control groups for all viewing conditions. Furthermore, the size of the gap effect was comparable for all groups and viewing conditions (both for short and long gap durations). In addition, consistent with previous results, the amblyopic eye has manifested an increased saccadic latency as compared to the nondominant eye in the control group. Regarding the occurrence of express saccades, the 200 ms gap condition was associated with an increased number of express saccades as compared to 50 ms gap and "no gap" conditions, both for amblyopic and control subjects. We did not observe any significant difference in terms of express saccades production between the control and amblyopic subjects. Our findings may suggest that amblyopia does not alter physiological mechanisms related to the efficiency of visual attention/fixation disengagement as supported by the observation that the gap effect and express saccades production was comparable between the normal and amblyopic subjects.

Not only amblyopic but also dominant eye in subjects with strabismus show increased saccadic latency.

Amblyopia is a developmental disorder of vision usually associated with the presence of strabismus and/or anisometropia during early childhood. Subject literature has shown that both the amblyopic and fellow eyes (especially in strabismic subjects) may manifest a variety of perceptual and oculomotor deficits. Previous studies using simple saccadic responses (pro-saccades) showed an increased saccadic latency only for the amblyopic eye viewing conditions. So far, there have appeared no saccadic latency studies in strabismic amblyopia for more complex volitional saccades. In order to maximize the contribution of the central retina in the process of saccade initiation, we decided to use delayed saccadic responses in order to test the hypothesis about saccadic latency increase in both eyes in strabismic amblyopes. The results from our study have shown that saccadic latency is increased both in the dominant and amblyopic eyes. In addition, the amblyopic eye in the strabismic group showed greater increase in saccadic latency compared to an amblyopic eye in the anisometropic group from our previous study. The observed increase in saccadic reaction time for the dominant eye is novel and provides further evidence that the visual pathway associated with the dominant eye might be also impaired in strabismic amblyopia. Since an abnormal binocular input during visual system development may affect gaze stability in both eyes, we speculate that unsteady fixation accompanied with subtle perceptual deficits contribute to an increase in saccadic latency that is observed in the dominant eye. Moreover, it appears that the cortical processes related to saccade decisions are delayed both for amblyopic and fellow eyes in strabismic subjects.

The amblyopic eye in subjects with anisometropia show increased saccadic latency in the delayed saccade task.

The term amblyopia is used to describe reduced visual function in one eye (or both eyes, though not so often) which cannot be fully improved by refractive correction and explained by the organic cause observed during regular eye examination. Amblyopia is associated with abnormal visual experience (e.g., anisometropia) during infancy or early childhood. Several studies have shown prolongation of saccadic latency time in amblyopic eye. In our opinion, study of saccadic latency in the context of central vision deficits assessment, should be based on central retina stimulation. For this reason, we proposed saccade delayed task. It requires inhibitory processing for maintaining fixation on the central target until it disappears-what constitutes the GO signal for saccade. The experiment consisted of 100 trials for each eye and was performed under two viewing conditions: monocular amblyopic/non-dominant eye and monocular dominant eye. We examined saccadic latency in 16 subjects (mean age 30 ± 11 years) with anisometropic amblyopia (two subjects had also microtropia) and in 17 control subjects (mean age 28 ± 8 years). Participants were instructed to look at central (fixation) target and when it disappears, to make the saccade toward the periphery (10°) as fast as possible, either left or the right target. The study results have proved the significant difference in saccadic latency between the amblyopic (mean 262 ± 48 ms) and dominant (mean 237 ± 45 ms) eye, in anisometropic group. In the control group, the saccadic latency for dominant (mean 226 ± 32 ms) and non-dominant (mean 230 ± 29 ms) eye was not significantly different. By the use of LATER (Linear Approach to the Threshold with Ergodic Rate) decision model we interpret our findings as a decrease in accumulation of visual information acquired by means of central retina in subjects with anisometropic amblyopia.