Comparison of subjective visual acuity with visual acuity predicted from C-scan topography.
OBJECTIVE
To compare the capability of objective measures of visual acuity (potential visual acuity from C-scan) to predict subjective visual acuity (best spectacle-corrected visual acuity [BSCVA]).


METHODS
Patients with BSCVA > or = 20/20 were enrolled in four groups (Group 1: normal [33 eyes]; Group 2: < -7.00 D myopia [43 eyes]; Group 3: > or = -7.00 D myopia [28 eyes]; Group 4: At least 1 month after LASIK [93 eyes]). Videokeratography was performed with the ray tracing Technomed C-scan. The potential visual acuity from C-scan was obtained with pupils undilated and intact precorneal tear films. All visual acuity was recorded in logMAR, and the significance of differences between acuities was assessed with a one-way ANOVA test.


RESULTS
The potential visual acuity from C-scan ray tracing of normal and myopic eyes in response to both photopic and mesopic stimuli did not differ. In a given eye, the potential visual acuity from C-scan ray tracing was better than BSCVA, and the difference was statistically significant. Although the potential visual acuity from C-scan of postoperative LASIK eyes in response to photopic stimuli was the same, it decreased under mesopic conditions.


CONCLUSIONS
Potential visual acuity from C-scan overestimates subjective visual acuity due to the inadequate assumptions in ray tracing or individual retinal resolution ability. In addition, the potential visual acuity from C-scan ray tracing varies with pupil diameter in different illumination.
Tsai
Show-Chuan
SC
Department of Ophthalmology, Taipei Municipal Jen-Ai Hospital, Taipei, Taiwan.
Wang
I-Jong
IJ
Liou
Shiow-Wen
SW
Chen
Wei-Li
WL
Lee
Yuan-Chieh
YC
Tseng
Gow-Lieng
GL
Hu
Fung-Rong
FR
D000293:Adolescent; D000328:Adult; D002648:Child; D003319:Corneal Stroma / Q000503:physiopathology / Q000601:surgery; D019781:Corneal Topography / Q000379:methods*; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology* / Q000601:surgery; D012029:Refraction, Ocular; D013524:Surgical Flaps; D014786:Vision Disorders / Q000175:diagnosis*; D014792:Visual Acuity / Q000502:physiology*