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L. F. Dell'Osso, Z. I. Wang; Dynamic Improvements in Visual Function After the Tenotomy and Reattachment Procedure: Model Predictions and Patient Data. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2835.
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Infantile nystagmus syndrome (INS) patients often cannot quickly locate new visual targets (they are "slow to see") or visually track moving objects (they cannot "catch up"). Dynamic demands on visual function are not measured by static measures, e.g., visual acuity; they require time-sensitive measures. We investigated how the dynamic properties of INS, saccadic latency (Ls) and both stationary (saccadic) and pursuit target-acquisition times (Lt), were affected by the tenotomy and reattachment (T&R) procedure. We used our behavioral ocular motor system (OMS) model to predict the responses of subjects with INS.
We compared the pre- and post-T&R responses of 4 INS subjects with different INS waveforms to test the model’s predictions. Infrared reflection was used for one INS subject, high-speed digital video for three. We analyzed the human subjects’ responses to large and small target-step and ramp stimuli. Ocular motor simulations were performed in MATLAB Simulink and analysis in MATLAB using OMtools software (downloadable from omlab.org).
Ls values were typically slightly higher than normal and unaffected by T&R. Saccadic and pursuit Lt values were a function of when in the INS cycle the moving stimuli occurred and were decreased by the T&R procedure. Model outputs and predictions accurately simulated human data. During smooth pursuit, stimuli occurring near intrinsic saccades resulted in steady-state errors in both the predicted model outputs and patient responses.
Intrinsic saccades disrupt the OMS’ ability to accurately calculate saccade amplitude and either refoveate or pursue targets. The T&R procedure reduces both stationary and pursuit target-acquisition times. OMS model simulations predicted novel stimulus-based effects on both types of target acquisition time in INS. Our model demonstrated emergent behaviors and predicted the therapeutic effects of T&R. The dynamics of INS foveation in INS-subject responses to changes in target position and velocity corresponded to both of the above patient complaints and to our model predictions.
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