|
Comparison
of Subjective Visual Acuity With Visual Acuity Predicted From
C-scan Topography
Show-Chuan
Tsai, MD; I-Jong Wang, MD, PhD; Shiow-Wen Liou, MD; Wei-Li
Chen, MD; Yuan-Chieh Lee, MD; Gow-Lieng Tseng, MD; Fung-Rong Hu,
MD
ABSTRACT
| PURPOSE |
| 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 20/20 were enrolled in four groups (Group 1: normal
[33 eyes]; Group 2: -7.00 D myopia [43 eyes]; Group 3: -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. [J Refract Surg 2003;19:137-141] |
From
the Department of Ophthalmology, Taipei Municipal Jen-Ai Hospital,
Taipei, Taiwan (Tsai, Liou, Tseng), Department of Ophthalmology,
National Taiwan University Hospital, Taipei, Taiwan (Wang, Chen,
Lee, Hu), and Department of Ophthalmology, Cathay General Hospital,
Taipei, Taiwan (Tsai).
The authors have no proprietary or financial interest in any product
mentioned herein.
Correspondence: I-Jong Wang, MD, Department of Ophthalmology,
National Taiwan University Hospital, 7, Chung-Shan South Road,
Taipei, Taiwan. Tel: 886.2.23970800 ext. 5729; Fax: 886.2.23412875;
E-mail: ijong@ha.mc.ntu.edu.tw
Received: November 26, 2001
Accepted: August 23, 2002
|
