Vision and visual skills in archery: Strydom 2010

Two South African optometrists measured eight visual abilities in 28 archers, eleven shooting compound, eight recurve and nine traditional, aged between 12 and 58 and ranging from beginners to experts, in order to build reference bands specific to archery. The bands run from superior to needs immediate attention and are set against those derived in 2002 from elite athletes in other sports.

The archers fall below those bands almost everywhere: visual acuity, contrast sensitivity, stereopsis and eye-hand coordination. On stereopsis the archers' lowest band reaches 160 seconds of arc against the 25 to 30 of the elite athletes. They come out above on two counts: eye-body coordination, where the superior band starts at 48 lights against 37, and visual response time with the right hand, under 0.180 seconds against 0.268, while with the left hand they sit just below the reference.

In the two tests built specifically for archery the figures speak more clearly. The error in judging distance grows with the distance: at 17 yards the average band runs from 2.80 to 5.05 yards of error, at 55 yards from 19.25 to 31.50. And in the 19 archers using a sight, groups of three arrows at 18 metres were tighter with one eye closed: the superior band sits under 14.43 millimetres with monocular aiming and under 58.74 with binocular.

The archers were recruited across disciplines, 21 men and seven women, 27 of them right-handed, and were allowed to keep their optical correction only if they already used it while shooting. Static acuity was taken with a Snellen chart at three metres and converted to six-metre values; contrast sensitivity with the Functional Acuity Contrast Test, five rows at rising spatial frequencies; stereopsis with the Randot test; eye-hand coordination and visual response time with a Wayne Saccadic Fixator, the panel of lights to be pressed; eye-body coordination with the same panel while standing on a balance board.

The two archery-specific tests are the ones worth describing. For distance judging, four tennis balls were placed in an open field at 17, 22, 32 and 55 yards, that is 16, 20, 29 and 50 metres, measured beforehand with a range finder; the archer had thirty seconds per object and wrote down an estimate. For monocular and binocular aiming, done only by the 19 archers using a sight, three arrows were shot at 18 metres at a white sheet of paper 90 by 50 millimetres with the non-dominant eye closed by a cap that did not interfere with the usual routine, and three more with both eyes open, measuring each time the distance between the centres of the two outside shafts.

The bands were built in two ways, both taken from the 2002 reference study: by percentiles when the test gave a minimum and a maximum, and by successive steps from the mean in the other cases.

The study measures nothing about performance: no competition score, no grouping beyond the aiming test itself, no correlation between any visual ability and any result. The authors close by saying that whether training these abilities improves performance remains an open question, and that is the most important thing the article does not address.

The bands are derived from the very 28 archers who would then be measured against them: they describe that group, they are not an outside reference. And that group mixes beginners with experts, three disciplines and ages from 12 to 58, to the point that the authors explain the low stereopsis by the presbyopia of some participants. The comparison with elite athletes in other sports comes from a separate study, on different people measured on another occasion, and on acuity the authors admit the value is limited by testing at three metres rather than six.

The test comparing one eye with two is the one an archer would most like to lean on, and it is the weakest: three arrows per condition, always in the same order, with no statistical test at all, and the authors note that one archer produced 305 millimetres with both eyes open and that without him the picture would change. The table for that test, moreover, skips the above average band and leaves a gap between 14.43 and 52.12 millimetres.

For someone who shoots, the useful part is the two tests built on a shooting field. The first shows how hard it is to judge a distance without a range finder, which concerns field archery and bowhunting more than target: at 50 metres the errors of a middle band of archers ran between 19 and 31 yards, that is between 18 and 29 metres, with error growing far faster than distance. The second records that at 18 metres groups were tighter with the non-dominant eye closed, a point coaches disagree about; with three arrows per condition and no statistical comparison, though, it is a hint and not an answer.

The rest of the article is a catalogue of reference bands built on 28 very different people. They do not tell us whether an archer with better figures shoots better, because the score was never measured, and they should not be used as a target to reach. The conclusion the authors themselves take away, that eye-body coordination is the only ability on which archers exceed the available references, points to balance rather than to sight.