Response time as a discriminator between true- and false-positive responses in suprathreshold perimetry.
OBJECTIVE
To report on differences between the latency distributions of responses to stimuli and to false-positive catch trials in suprathreshold perimetry. To describe an algorithm for defining response time windows and to report on its performance in discriminating between true- and false-positive responses on the basis of response time (RT).


METHODS
A sample of 435 largely inexperienced patients underwent suprathreshold visual field examination on a perimeter that was modified to record RTs. Data were analyzed from 60,500 responses to suprathreshold stimuli and from 523 false-positive responses to catch trials.


RESULTS
False-positive responses had much more variable latencies than responses to suprathreshold stimuli. An algorithm defining RT windows on the basis of z-transformed individual latency samples correctly identified more than 70% of false-positive responses to catch trials, whereas fewer than 3% of responses to suprathreshold stimuli were classified as false-positive responses.


CONCLUSIONS
Latency analysis can be used to detect a substantial proportion of false-positive responses in suprathreshold perimetry. Rejection of such responses may increase the reliability of visual field screening by reducing variability and bias in a small but clinically important proportion of patients.
Artes
Paul H
PH
Academic Department of Ophthalmology, Manchester Royal Eye Hospital, University of Manchester, Manchester, United Kingdom. paul_h_artes@yahoo.co.uk
McLeod
David
D
Henson
David B
DB
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D002648:Child; D005189:False Positive Reactions; D006801:Humans; D008875:Middle Aged; D011237:Predictive Value of Tests; D011930:Reaction Time; D015203:Reproducibility of Results; D014786:Vision Disorders / Q000175:diagnosis; D058609:Visual Field Tests / Q000592:standards*; D014794:Visual Fields