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Mark S. Bolding, Kristine B. Hopkins, Adrienne C. Lahti, Lei Liu, Paul D. Gamlin; Decreased Vergence Tracking Gain in a Cohort of Patients with Schizophrenia. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4858.
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Compared to healthy controls, patients with schizophrenia have lower smooth pursuit gain and increased rates of catch up saccades (CUS) (O’Driscoll and Callahan, 2008). They have also been reported to exhibit a higher prevalence of convergence insufficiency (Flach et al., 1992). To date, however, there have been no reports on vergence tracking gain in such patients. Therefore, we investigated both static and dynamic vergence behavior in healthy controls and patients with schizophrenia.
41 subjects participated in the study. Exclusion criteria included acuity of less than 20/40 in either eye and lack of stereovision. 20 participants had been diagnosed with schizophrenia (SZ) and 21 were matched healthy controls (HC). Binocular vision testing included cover test at distance and near, near point of convergence, positive fusional vergences at near (prism bar), and stereo acuity. Eye movements were recorded in multiple tasks including triangular waveform 20° smooth pursuit at a frequency of 1.0, 0.5, and 0.2 Hz and vergence tracking of a real target that moved between 10 and 30 cm at a frequency of 0.25, 0.1, 0.05 Hz. Eye position data were collected at 500 Hz using a binocular video eye tracker. Pursuit gains were calculated after removal of saccades from the data. Group differences were compared using Wilcoxon rank sum tests.
Consistent with previous reports, the SZ group exhibited lower gains and an increased rate of CUS for 0.5 and 1.0 Hz smooth pursuit tasks (0.5 Hz gain: HC=0.73, SZ=0.64, p<0.05; 1.0 Hz gain: HC=0.45, SZ=0.35, p<0.05). For vergence tasks, when compared to the HC group, the SZ group did not demonstrate a significantly greater incidence of convergence insufficiency, but did exhibit significantly lower gains during all vergence tracking tasks. Gain differences increased with higher target speeds (0.05 Hz: gain: HC=0.90, SZ=0.67, p<0.05; 0.1 Hz gain: HC=0.88, SZ=0.65, p<0.05; 0.25 Hz gain: HC=0.86, SZ=0.59, p<0.01). HC subjects exhibited significant correlation in gain within the smooth pursuit and the vergence tracking tasks (R=0.67; p<0.005), but not between these tasks (R=0.19). In contrast, SZ subjects exhibited significant correlation in gain both within (R=0.68; p<0.005 ) and between (R=0.45; p<0.05) the smooth pursuit and vergence tracking tasks.
We did not observe a significantly increased rate of convergence insufficiency in patients with schizophrenia. However, our observations clearly demonstrate previously unreported vergence tracking deficits in such patients.
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