A comparison of the Frisby, Random-Dot E, TNO, and Randot circles stereotests in screening and office use.

Three random-dot stereogram (RDS) tests, the Frisby, Random-Dot E (RDE), and TNO tests, and a stereotest with monocularly visible contours, the Randot circles test, were administered to two populations of 3- to 5-year-old children in vision screening settings and to a sample of patients with strabismus and amblyopia. The Frisby test missed (underreferred) cases of binocular dysfunction detected by the RDE and TNO tests, using a 250 seconds of arc (250") (Frisby and RDE) or 240" (TNO) thresholds as the pass-fail breakpoint. The TNO underreferred cases at 240" relative to the RDE, but underreferred none if the TNO's breakpoint was lowered to 120". The Randot circles test produced better-indicated stereoacuities than the RDS tests and was found able to reliably grade stereoacuity in patients with stereopsis too poor to be graded by RDS tests.