Visual Field Mapping by Tangent Screen and Humphrey Perimetry: A Comparative Study

Abstract

Background and Objectives: (a) To compare manual tangent screen perimetry and automated Humphrey perimetry for visual field testing, and (b) to analyze whether manual tangent screen perimetry still has a role or it should be replaced by computerized automated Humphrey perimetry in physiology labs and clinical diagnostic settings.

Methods: Study was done on 45 patients between 18 and 65 years of age that included 30 eyes of patients suffering from glaucoma/ other eye diseases giving rise to visual field defects, 5 eyes of patients suffering from neurological diseases and 10 eyes of normal subjects.

All patients underwent perimetry examination by tangent screen at 1 meter distance (and 2 meter distance, if required) and automated Humphrey perimetry by Humphrey visual field analyzer (HFA) using 30-2 ‘white on white’ full threshold strategy. Tangent screen consists of black screen 2 meter square or 1 meter square. Accordingly, patient is seated at a distance of 2 meter or 1 meter respectively. A patient with organically constricted visual fields will show an increase in the size of the visual field when moved to a farther distance while a patient with functional visual field loss will often report the same absolute size of the field (tubular or gun-barrel field) to be consistent with their first field. This is clear evidence of functional visual field impairment.

Results: Out of 45 patients, 29 were male and 16 were female. The age cases in the study ranged from 40-79 years with mean age of 60.70 years. Tangent screen perimetry was able to detect about 5 patients with early field defects and 15 patients with moderate/ advanced field defects. On the other hand, Humphrey automated perimetry was able to detect 10 patients with early field defects and 18 patients with moderate/ advanced field defects. While only 13.33% technicians preferred tangent screen perimetry, around three-fourths of the technicians found Humphrey automated perimetry more preferable. 91.11% technicians found HVF to be technically easier because the automated perimeter eliminates observer bias, is easier to perform and also overcomes the tedium of manual perimetry. Moreover, automated perimetry also uses quantified parameters while manual perimetry does not. On evaluating sensitivity and specificity of manual tangent screen perimeter using the Humphrey automated perimeter as the standard, the tests showed that the tangent screen perimeter had 75.75% sensitivity and 88.88% specificity. Since the mean time taken was more in automated perimetry: 474.5 sec, 474 sec and 459.9 sec versus 340.5 sec, 339.1 sec, and 339.1 sec in glaucoma, neurological and normal patients respectively; more patients-66% preferred tangent screen perimetry.

Interpretation and Conclusions: Our results suggest that visual field testing with automated perimetry is superior to visual field testing with tangent screen perimetry. The automated perimeter picked up visual field defects in a larger number of eyes than the tangent screen perimeter. Visual field defects were more extensive on automated perimetry compared to tangent screen perimetry.

The advantage of the HVF analyzer also lies in its ability to make use of quantified parameters like mean deviation and corrected pattern standard deviation to detect subtle worsening of visual field defect, with statistical level of confidence.