Peripheral astigmatism in emmetropic eyes.
The long-term aim of the work introduced here is to investigate the influence of off-axis aberrations on human vision, especially for subjects with a large central scotoma. The latter use their peripheral vision in spite of its poor off-axis optical quality, and a correction of the off-axis aberrations might be of great assistance. The eccentric fixation angles used by these subjects can be up to 20-30 degrees. In this initial study we have measured oblique astigmatism, the major off-axis aberration, in 20 emmetropic eyes in 10 degrees steps out to 60 degrees nasally and temporally using a 'double pass' setup. The results show very large individual differences and the oblique astigmatism also varies from nasal to temporal side. In an off-axis measurement angle of 30 degrees the astigmatism varied between subjects from 1 to 7-D, with a mean astigmatism of about 4-D on the nasal side and about 1.5-D lower on the temporal side. At 60 degrees temporally, the mean astigmatism was 7-D. At 60 degrees nasally, all subjects had astigmatism larger than 8-D and the mean astigmatism was 11-D. The results indicate that any attempt to correct the off axis astigmatism in an eye with central scotoma cannot be based on central refraction; instead, individual measurements are necessary.
Gustafsson
J
J
Center for Rehabilitation Engineering Research (Certec), Lund Institute of Technology, Sweden. jorgen.gustafsson@certec.lth.se
Terenius
E
E
Buchheister
J
J
Unsbo
P
P
D000328:Adult; D001251:Astigmatism / Q000150:complications* / Q000175:diagnosis / Q000503:physiopathology; D005403:Fixation, Ocular; D006801:Humans; D008875:Middle Aged; D012029:Refraction, Ocular; D012607:Scotoma / Q000150:complications* / Q000503:physiopathology; D014787:Vision Tests / Q000379:methods; D014794:Visual Fields