Validation and Repeatability of the Paul Harris Stereotest

Abstract

Purpose : The Paul Harris (PH) Randot test is a vectographic booklet for measuring stereopsis that, similarly to the TNO stereotest but unlike the Titmus stereofly and traditional Randot (tRandot) tests, is devoid of monocular cues. This prospective observational study investigated the intra-test repeatability and inter-test agreement for the PH Randot test compared with the other clinical stereotests.

Methods : Seventy subjects (mean age: 24±7, range: 18-53, 54 female) with normal binocular vision were measured three times with each stereotest, in random order. Thirty subjects were re-measured after a week. Bland-Altman (B-A) analysis and a repeated measures ANOVA with one factor, determined the interchangeability between the PH Randot and other stereotests by determining the mean difference between the measurements of two stereotests (m_diff-tests) and their confidence intervals. Intra-test repeatability was assessed by comparing the mean difference between the 1^st and 2^nd measurements (m_{diff-measurements}) and their standard deviation (stdev_measurements).

Results : Mean stereothreshold measurements differed significantly between the TNO and PHRandot and the other booklets (mean stereothresholds- TNO: 51.3±14.5", Stereofly: 36.0±15.5", tRandot: 33.6±16.8",PHRandot: 22.7±5.7"; F_(df=3,69)=77.8, p<0.0001, Tukey HSD<0.01). The Titmus and tRandot were not significantly different from one another. B-A analysis found that the PHRandot yielded systematically lower thresholds in subjects with stereopsis lower than 40", which may be due to a difference in step sizes between the booklets. Nevertheless, the m_diff-tests between the PHRandot and the tRandot (11") and Titmus (13") was lower than the minimal step size (20") and over 94% of the observations were within ±20" of each other. This was not the case for the TNO (m_PHRandot-TNO=28"). The comparison between the 1^st and 2^nd measurement sessions yielded the smallest m_diff and stdev_measurements for the PH Randot test (PHRandot= 2.72” ± 11.4”, tRandot = 10.61± 40.8, Titmus= 18.28 ± 33.3, TNO=-14.39 ± 68.1), indicating better repeatability.

Conclusions : Normal subjects with above normal stereopsis often achieve lower thresholds using the PHRandot stereotest than with other stereotests. Nevertheless, the PHRandot test can be used interchangeably with the tRandot and Titmus tests but not with the TNO test. The PHRandot yielded the best inter-test repeatability, indicating more precision.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.