Subjective blur limits for cylinder.

PURPOSE

The purpose was to compare subjective blur limits for cylinder and defocus.

METHODS

Blur was induced with a deformable, adaptive-optics mirror when either the subjects' own astigmatisms were corrected or when both astigmatisms and higher-order aberrations were corrected. Subjects were cyclopleged and had 5-mm artificial pupils. Black letter targets (0.1, 0.35, and 0.6 logMAR) were presented on white backgrounds.

RESULTS

For 10 subjects, blur limits were approximately 50% greater for cylinder than for defocus (in diopters). Although there were considerable effects of axis for individuals, overall, this was not strong, with the 0 degrees (or 180 degrees ) axis having approximately 20% greater limits than oblique axes. In a second experiment with text (equivalent in angle to N10 print at 40 cm distance), cylinder blur limits for six subjects were approximately 30% greater than those for defocus; this percentage was slightly smaller than for the three letters. Blur limits of the text were intermediate between those of 0.35- and 0.6-logMAR letters. Extensive blur limit measurements for one subject with single letters did not show expected interactions between target detail orientation and cylinder axis.

CONCLUSIONS

Subjective blur limits for cylinder are 30 to 50% greater than those for defocus, with the overall influence of cylinder axis being 20%.