Prismatic displacement effect of progressive multifocal glasses on reaction time and accuracy in elderly people

Abstract

BackgroundMultifocal glasses (bifocals, trifocals, and progressives) increase the risk of falling in elderly people, but how they do so is unclear. To explain why glasses with progressive addition lenses increase the risk of falls and whether this can be attributed to false projection, this study aimed to 1) map the prismatic displacement of a progressive lens, and 2) test whether this displacement impaired reaction time and accuracy.MethodsThe reaction times of healthy ≥75-year-olds (31 participants) were measured when grasping for a bar and touching a black line. Participants performed each test twice, wearing their progressives and new, matched single vision (distance) glasses in random order. The line and bar targets were positioned according to the maximum and minimum prismatic displacement effect through the progressive lens, mapped using a focimeter.ResultsProgressive spectacle lenses have large areas of prismatic displacement in the central visual axis and edges. Reaction time was faster for progressives compared with single vision glasses with a centrally-placed horizontal grab bar (mean difference 101 ms, P=0.011 [repeated measures analysis]) and a horizontal black line placed 300 mm below center (mean difference 80 ms, P=0.007). There was no difference in accuracy between the two types of glasses.ConclusionOlder people appear to adapt to the false projection of progressives in the central visual axis. This adaptation means that swapping to new glasses or a large change in prescription may lead to a fall. Frequently updating glasses may be more beneficial.

Satisfaction Level of Progressive Additional Lens (PALs) Wearers

“…However, most of them were uncomfortable with distortion at the peripheral vision. A study conducted by Ellison, (2012) justified the same effect on PALs wearers. Activities such as driving or walking by using progressive additional lens cause the vision to appear to oscillate at the sides.…”

Intermediate addition multifocals provide safe stair ambulation with adequate ‘short‐term’ reading

“…They may also provide sufficient near vision to avoid non‐fall related injuries, the incidence of which were found to increase with the distance single vision intervention in the Haran and colleagues' RCT . It is also important to note that in the Haran RCT, sedentary participants fell more outdoors (51% vs 36%), suggesting that the intervention generated false confidence and risk taking and/or that for those more likely to fall, the near focused region of multifocals may assist in response times and precision for grabbing a support/hand rail and avoiding a trip becoming a fall . and/or that the relatively few times that the sedentary participants ventured outdoors meant they had little chance to adapt to wearing the new spectacles.…”

“…10,11 It is also important to note that in the Haran RCT, sedentary participants fell more outdoors (51% vs 36%), suggesting that the intervention generated false confidence and risk taking 11 and/ or that for those more likely to fall, the near focused region of multifocals may assist in response times and precision for grabbing a support/hand rail and avoiding a trip becoming a fall. 22 and/or that the relatively few times that the sedentary participants ventured outdoors meant they had little chance to adapt to wearing the new spectacles. Note that swapping from a full addition PAL to distance single vision lenses when venturing outdoors and then swapping back again when returning home requires two adaptations (including magnification 23 and vestibulo-ocular reflex 24 adaptations) from the wearer.…”

Falls Among the Elderly and Vision: A Narrative Review

“…Second, such efforts are likely to reduce morbidity and mortality rates attributable to falls among community-dwelling elderly at high risk for falling, thus improving functional status and promoting independent living. Third, the application of improved efforts to maximize vision, and to minimize the degree to which environmental factors and partially mediating risk factors such as functional limitations, and type of visual aid, may increase falls risk among those with limited vision, an individual's risk of falling may be vastly reduced as outlined by Keay et al [106], Steinman et al [107], and Ellison et al [108].…”