Age related effects of restricted head movements on the useful field of view of drivers.

Eighty drivers in a sample of four groups of 20 (10 males, 10 females), aged under 30 years ('young'), 40-59 ('middle aged'), 60-69 ('older'), and 70 years and over ('oldest'), participated in tests of head rotation and of several visual functions relevant to safe driving. Head rotation data showed that the oldest drivers had lost about 1/3 of movement and that the loss tended to be more evident in males. Second attempts almost always produced slightly better results. All participants had at least 20/40 binocular vision, however, tests of monocular visual acuity, stereovision, and horizontal peripheral vision revealed that the poorest performers were aged 60 years and over and that the degree of decrement increased with age. Many of the older and oldest drivers in the sample were both severely restricted in their ability to turn their head and evidenced a loss of visual functioning. Analysis of the effect of reduced head movement on the useful field of view indicated that, for the drivers aged 60 years and over, there was an evident restriction on the distances at which approaching traffic could be brought into the central, stationary field, so that even at maximum head rotation plus one saccade (15 degrees), approaching vehicles would not be clearly perceived beyond a distance of 50 m. The findings are discussed in relation to older drivers' involvement in intersection accidents.