Abstract
Purpose: :
Novel psychophysical stimuli that differentiate dysfunctional retinal ganglion cell activity from total lack of activity may be a superior method to detect and monitor the progression of visual impairment. We develop an equivalent noise paradigm that targets motion sensitivity in a group of patients with ocular hypertension and early glaucoma.
Methods: :
In a 2 alternative forced choice task and with fixation monitored by an eye tracker, patients with glaucomatous damage (N=14, mean age 61), ocular hypertension (N=25, mean age 57) and age-matched controls (N=12, mean age 58), all with normal or corrected foveal visual acuity, identified the direction (clockwise or counter-clockwise) of limited lifetime, moving random dots. Stimuli were presented at 0 and ±8 deg eccentricity, in areas of normal threshold on the Humphrey visual field plot. Dot directions were drawn from a normal distribution whose mean and standard deviation were varied by a computer staircase. Minimum directional offset for directionally noiseless stimuli and maximum tolerable noise for 180 deg direction identification were fit with equivalent noise functions to estimate internal noise (indicative of neural dysfunction) and sampling efficiency (indicative of neural non-function).
Results: :
At all retinal loci, direction discrimination thresholds were significantly higher in patients with Glaucoma (p<0.05), but not significantly different between hypertensive and control eyes (p<0.1). Equivalent noise analysis revealed significantly elevated levels of internal noise between glaucomatous and both control (p<0.01) and hypertensive (p<0.05) eyes. In Glaucomatous eyes, internal noise was significantly higher in upper (p<0.01) and lower (p<0.05) visual field than in fovea. Sampling efficiency estimates were not significantly different across groups or retinal loci.
Conclusions: :
In retinal areas with no measurable Humphrey visual field loss, there is a motion sensitivity deficit in glaucomatous eyes. The impairment is caused by an elevation of neural noise, indicating the presence of neural dysfunction that has yet to progress to non-function. Equivalent noise analysis may therefore offer a sensitive diagnostic for detecting the presence and progression of glaucomatous vision loss.
Keywords: motion-2D • visual fields • perimetry