A search for differences in size perception of near objects in young myopes corrected by either spectacles or contact lenses.
Accommodation and convergence demands are lower for a spectacle-corrected myope than for the same individual when corrected with contact lenses. Thus the impact of accommodative/convergence micropsia ought to be lower with the spectacle correction. A size-matching experiment which required myopic subjects (corrections up to -12.25 D) to match the sizes of each of four standard targets with a variable comparison target was therefore conducted. The standard targets were placed at four viewing distances: 3 m, I m, 0.5 m and 0.25 m. All standard targets subtended 2 degrees at the eye. The variable comparison target was situated at a fixed distance of 2 m and was generated on a visual display unit. Each of the eight subjects was shown one standard target at a time under binocular viewing conditions and was told to adjust the size of the comparison target until he/she felt that both targets were equal in linear size. Two sets of readings were taken: one when the subject's myopia was corrected with spectacles and one when corrected with contact lenses. No systematic difference in size perception was found between the spectacle and contact lens corrected cases, implying that the relatively small differences in accommodation and convergence demand did not significantly influence the size judgements.
Koh
L H
LH
Department of Optometry and Vision Sciences, UMIST, PO Box 88, Manchester, M60 1QD, UK.
Charman
W N
WN