Factors influencing normal perimetric thresholds obtained using the Humphrey Field Analyzer

The relationships between dioptric blur, pupil size, retinal eccentricity, and retinal sensitivity were investigated in the central 5 degrees of the visual field in 10 normal subjects using the Humphrey Field Analyzer. Pupil size did not influence the foveal sensitivity or retinal profile in the unblurred condition. The slope of the retinal profile was significantly steeper in the 3 mm pupil size condition (-0.62 dB/degree) than when compared to the 8 mm pupil size condition (-0.34 dB/degree), when averaged over all dioptric blur conditions. The depth of focus for the 3 mm pupil size condition (3.86 diopters) was significantly greater than that found for the 8 mm pupil size condition (1.82 D). The retinal threshold doubling eccentricity (E2) was calculated to be similar to that of grating acuity and contrast sensitivity (3.71). The data suggest that while large depth of focus effects in small pupil sizes appear to reduce the need for accurate refractive error corrections in determining perimetric retinal sensitivities, variations in the slope of the retinal profile under conditions of uncontrolled dioptric blur and pupil size may result in the artifactual sensitivity decreases. Therefore, it is recommended that measurement of pupil size and accurate correction of near refractive errors be performed to minimize the possibility of incorrect detection of central visual field defects.