Effect of instructions on conventional automated perimetry

To investigate the effect of perimetrists' instructions on automated perimetry thresholds.

Eighteen volunteers in two age groups participated in a series of three test sessions. Each session consisted of a Humphrey Field Analyzer 30-2 test, a questionnaire, and a customized test program using a Humphrey perimeter to construct frequency of seeing (FOS) curves from which thresholds were calculated, and a descriptive measure of response criterion was derived. The FOS curves were obtained at a central and a peripheral test location within the same test session. The three test sessions differed only by the instructions given. The instructions were adapted from those listed in the manufacturer's instruction manual and were designed to influence participants to respond to the stimuli in a conservative, liberal, or neutral manner.

For the 30-2 threshold test, a significant difference in mean deviation was found among the three instruction types (P = 0.001) and between the two age groups (P = 0.001). Although differences were small in the younger subjects (2.04 dB), the means for the responses from liberal to conservative differed by 6.57 dB in the older subjects. Thresholds obtained in a peripheral location by the customized threshold test were found to differ significantly between the age groups (younger group mean, 31.0 dB; older group mean, 27.2 dB) and among the instruction types (liberal mean, 30.9 dB; conservative mean, 28.1 dB; and neutral mean, 30.3 dB; P < 0.001). The descriptive measurement of response criterion suggests that a difference in criteria occurred as a result of the instructions in both peripheral and central locations for both age groups (P = 0.0001). In addition, according to self-reports, liberal instructions caused participants to be more likely to respond, whereas the conservative instructions caused them to be more reluctant to respond.

Perimetrists' instructions can significantly affect obtained automated perimetry thresholds.