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We have undertaken the first study to determine, in an operational scenario, the visual acuity required by beach lifeguards in order to identify a human head at the outer edge of a patrolled area of 300 m out to sea. The required visual acuity as determined by the angle subtended by a human head at this distance would be 6/17, but as a result of location and detection factors we hypothesised that it would have to be better than this.
The experiment received ethical approval and 21 beach lifeguards (16 men, 15 women, all under 35 years) gave their consent to participate. After eye tests to ensure normal vision (mean [range] visual acuity 6/4.8 [6/3.8–6/5]), they undertook a series of tests on beaches at Bournemouth (n = 9) and Westward Ho! (n = 12), during which their vision was blurred (using spherical lenses placed within a trial frame) to a visual acuity at which they could not identify the targets presented to them (approximately 6/70); these were human heads or equivalent‐sized buoys. The subjects looked out to sea or across a wet beach and their visual acuity was improved every minute by reducing the refractive blur in 0.25 dioptre increments until they could identify the target to the point at which they would investigate it further using binoculars. The tests were performed on the same day, in good weather, uniform lighting conditions and a sea state of 0–1 (calm).
Results are presented in table 11,, data were normally distributed (Anderson–Darling normality test).
The variability between subjects is likely to have been caused by the differing ability of individuals to adjust to the lenses, and the central processing required to search, see and identify a head in the sea. This also explains why the visual acuity required to see a human head at 300 m in the sea was 6/7, rather than the theoretical figure of 6/17. We therefore accept the hypothesis.
It is therefore recommended that a beach lifeguard should have visual acuity of 6/7 or better. As this will exclude some individuals, consideration could be given to allowing beach lifeguards to wear glasses. It seems logical to base the requirement for uncorrected eyesight on what the beach lifeguard must see when they have removed their glasses and are moving towards a casualty. By then the beach lifeguard will have detected the casualty. As the visual acuity required to maintain sight of a casualty is less than that required to locate/detect them in the first place, it is reasonable to require a beach lifeguard to have uncorrected vision, in their worst eye, that is at least equivalent to that required to see a head from 200–300 m distance, or an arm waving from 300 m. The average for these activities is 6/14.
In terms of the Snellen chart, we recommend that the corrected vision for beach lifeguards be 6/9 best eye, 6/18 worst eye, and the unaided acuity be no worse than 6/18 in either eye.
The authors would like to thank the volunteers, Dr Frank Eperjesi (Aston University), Adam Wooler, Peter Dawes, Chris Lewis and the RNLI who funded the project.
Funding: This work was funded by the Royal National Lifeboat Institution.
Competing interests: None.