Refractive error, cognitive demand and nearwork-induced transient myopia.
OBJECTIVE
Whereas many previous studies have identified the association between sustained near work and myopia, few have assessed the influence of concomitant levels of cognitive effort. This study investigates the effect of cognitive effort on near-work induced transient myopia (NITM).


METHODS
Subjects comprised of six early onset myopes (EOM; mean age 23.7 yrs; mean onset 10.8 yrs), six late-onset myopes (LOM; mean age 23.2 yrs; mean onset 20.0 yrs) and six emmetropes (EMM; mean age 23.8 yrs). Dynamic, monocular, ocular accommodation was measured with the Shin-Nippon SRW-5000 autorefractor. Subjects engaged passively or actively in a 5 minute arithmetic sum checking task presented monocularly on an LCD monitor via a Badal optical system. In all conditions the task was initially located at near (4.50 D) and immediately following the task instantaneously changed to far (0.00 D) for a further 5 minutes. The combinations of active (A) and passive (P) cognition were randomly allocated as P:P; A:P; A:A; P:A.


RESULTS
For the initial near task, LOMs were shown to have a significantly less accurate accommodative response than either EOMs or EMMs (p < 0.001). For the far task, post hoc analyses for refraction identified EOMs as demonstrating significant NITM compared to LOMs (p < 0.05), who in turn showed greater NITM than EMMs (p < 0.001). The data show that for EOMs the level of cognitive activity operating during the near and far tasks determines the persistence of NITM; persistence being maximal when active cognition at near is followed by passive cognition at far.


CONCLUSIONS
Compared with EMMs, EOMs and LOMs are particularly susceptible to NITM such that sustained near vision reduces subsequent accommodative accuracy for far vision. It is speculated that the marked NITM found in EOM may be a consequence of the crystalline lens thinning shown to be a developmental feature of EOM. Whereas the role of small amounts of retinal defocus in myopigenesis remains equivocal, the results show that account needs to be taken of cognitive demand in assessing phenomena such as NITM.
Wolffsohn
James S
JS
Neurosciences Research Institute, School of Life and Health Sciences, Aston University, Birmingham, UK. j.s.w.wolffsohn@aston.ac.uk
Gilmartin
Bernard
B
Thomas
Rachel
R
Mallen
Edward A H
EA
D000065:Accommodation, Ocular / Q000502:physiology*; D000221:Adaptation, Ocular / Q000502:physiology; D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D003071:Cognition / Q000502:physiology*; D006801:Humans; D009216:Myopia / Q000209:etiology / Q000503:physiopathology*; D011932:Reading; D015348:Vision, Binocular / Q000502:physiology