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Haoran Wu, Xiaoning Li, Yao Tang, Bin Zhang, Zhikuan Yang; Abnormal temporal integration for stereoscopic vision in intermittent exotropia. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4430.
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© ARVO (1962-2015); The Authors (2016-present)
Despite periodical misalignment of the two eyes, some intermittent exotropia (IXT) patients exhibit normal stereoacuity, particularly when evaluated with a static test, such as Titmus. However, such test does not limit the target viewing duration, and it is known that normal subject’s stereoacuity improves with viewing duration and often reaches the best level around 100 milliseconds. Therefore, it is important to study if the temporal integration process is altered in IXTs.
Twenty-eight IXT patients (aged 7 to 28 years old) participated in this study. The inclusion criteria were: 1) no amblyopia, 2) anisometropia≤1D, 3) no incomitance of the deviation; 4) vertical deviation of <5 pd; 5) with stereopsis indicated by synoptophore, 6) no convergence insufficiency-type IXT 7) no history of strabismic surgery. Thirty-four aged matched normal subjects served as controls. Firstly, static stereopsis was measured with Titmus and TNO stereoacuity test. Next, to evaluate the temporal integration of stereopsis, dichoptic random dots stimuli were presented with varying durations ranging from 50 to 1500ms. For each stimulus presentation duration, the threshold to detect disparity was measured using a 3-down-1-up staircase algorithm. The stereo thresholds (th) versus viewing durations were fitted into a quadratic model of th= h0*sqrt(t-2+Tmin-2), where th was the stereoacuity at a given presentation duration (t), Tmin was critical time constant at which the stereoacuity no longer changes, and h0 determines the vertical height of the flat portion (Dmin), which is the best achievable stereoacuity.
For Titmus test, IXT subjects did not differ from normal subjects significantly (median: 160 vs 80 arcsec, p=0.28). For TNO test, the IXT subjects performed significantly worse (median: 25 vs 12.5 arcsec, p<0.01). For temporal integration test, Dmin was significantly worse in IXT subjects than in the normals (237.3±116.2 vs. 51.2±18.7 arcsec, p<0.01). Tmin was significantly longer in IXT subjects than in the normals (488.5±318.9 vs. 124.7±71.2 ms, p<0.01).
The temporal integration for stereopsis is impaired in IXT subjects, with longer time (Tmin) needed to achieve elevated best achievable stereoacuity (Dmin).
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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