Three-rods test as drivers' license vision test from the viewpoint of reproducibility, eye deviation, and functional visual acuity

Abstract

BackgroundThree-rods test is required as depth perception vision test to obtain motor vehicle license to drive taxies, buses, and trucks in Japan. Functional visual acuity is measured automatically by successive visual target presentation in a fixed period of time. This study examined three-rods test from the viewpoint of reproducibility, eye deviation, and functional visual acuity to assess the feasibility for drivers' license vision test.MethodsAt three-rods test, a central rod was moved at the speed of 50 mm/sec forward and backward automatically against two fixed rods on both sides inside an illuminated box. An examinee at the distance of 2.5 m observed the rods inside the box from a small window and pushed a button to stop the central rod in alignment with the fixed rods. Erred distance of the central rod from the fixed rods as a mean of 4 measurements was used. At functional visual acuity test, an examinee moved a joystick to the same direction as Landolt-C opening as a visual target which was sequentially presented every 2 seconds for 30 times in 1 minute.ResultsThe mean erred distance of three-rods test was reproducible between two tests done on separate occasions (n = 44, ρ = 0.679, P < 0.0001, Spearman rank correlation). Exophoria induced by wearing 4-prism-diopter base-out prism did not significantly influence the mean erred distance while vertical diplopia induced by wearing 4-prism-diopter base-up prism disrupted the measurement (n = 9). The mean erred distance of three-rods test was better correlated with functional visual acuity tested with both eyes open than with conventional visual acuity with both eyes open (n = 17, ρ = 0.2 versus ρ = 0.179).ConclusionIn the context of the small sample size in the present study, the three-rods test was reproducible, and testable in the presence of phoria, but not testable in diplopia, indicating the feasibility as a depth perception vision test.

Factors affecting depth perception and comparison of depth perception measured by the three-rods test in monocular and binocular vision

“…Regarding the validity of the three-rods test, Matsuo et al previously reported that this test was reproducible and feasible enough for an appropriate screening test of depth perception in the general population, although it is not as accurate as stereo tests used in an ophthalmic practice [7]. The authors also reported that the three-rods test had a better correlation with functional VA tested with both eyes open [6]. Similarly, we also find a relationship between binocular distance functional VA and performance on the modified three-rods test employed in our study.…”

“…The design and structure of the system were basically the same as the three-rods test used previously [ 6 ]. Due to the viewing distance being greater than in the standard three-rods test, the apparatus was scaled up in size so that it would have the same optical size (at a maximal distance of 20 m) as the apparatus in the standard three-rods test.…”

“…Driving tasks are characterised by dynamic situations in which moving vehicles are operated in an environment with both static and moving objects. Several vision-related tests are employed routinely for individuals to qualify for a driver's license [ 5 , 6 , 7 , 8 ]. The three-rods test is used to examine depth perception, and it is used routinely to qualify for a driver's license in Japan in addition to visual acuity (VA) testing.…”

Various Factors that Interfere with the Accurate Assessment of the Three-rods Test and Modified Three-rods Test to Resolve Monocular Cues

“…Previous research has shown that the statistically signi cant positive correlation of results between threerods test and stereotests used in daily ophthalmic practice (distance Randot Stereotest and Titmus Stereotest) 16 . The authors also reported that the results of the three-rods test done on separate days were positively correlated 17 . These studies collectively support the validity of the use of the three-rods test as a means of evaluating binocular stereoacuity.…”