Fig. (1) a) Plots of NAFX vs Gaze Angle during fixation of far targets with no therapeutic aids, with contact lenses, with acetazolamide, and during convergence at 60 PD. The equivalent visual acuities shown are for subjects over 60 years of age. Curves are 2^nd order polynomial fits to the data. N = “null” originally measured in 1963. b) Examples of the pre- and post-acetazolamide (heavy line) INS waveforms. Large spikes are blinks or video dropouts.