Quantitative topographic irregularity as a predictor of spectacle-corrected visual acuity after refractive surgery.
OBJECTIVE
To evaluate a new topographic index called topographic irregularity as a quantitative predictor of corrected vision after refractive surgery.


METHODS
We defined topographic irregularity as the summed difference at all points between a topographic refractive corneal power map and its best-fit spherocylinder. We prospectively studied 107 eyes of 107 patients 3 months after a variety of refractive procedures. Topographic irregularity was calculated from topographic maps, and the correlation between topographic irregularity and spectacle-corrected visual acuity was determined using both high-contrast and low-contrast acuity charts. This correlation was compared with correlations for the surface regularity index and the surface asymmetry index. Next, we analyzed 54 of these topographic maps to create a regression scale relating surface regularity index, surface asymmetry index, and topographic irregularity to predict spectacle-corrected visual acuity. This scale was then used to predict spectacle-corrected visual acuity on the remaining 53 postoperative patients.


RESULTS
The correlation of topographic irregularity with spectacle-corrected visual acuity (R(2) =.36) was comparable to the correlation for the surface regularity index (R(2) =.36) and stronger than for the surface asymmetry index (R(2) =.11) when spectacle-corrected visual acuity was measured with high-contrast eye charts. Topographic irregularity correlated more strongly with spectacle-corrected visual acuity (R(2) =.42) than either the surface regularity index (R(2) =.28) or the surface asymmetry index (R(2) =.14) when spectacle-corrected visual acuity was measured with low-contrast eye charts. Using the regression scale, prediction of high-contrast and low-contrast spectacle-corrected visual acuity from topographic irregularity was superior to or comparable to predictions using the surface regularity index and the surface asymmetry index.


CONCLUSIONS
Topographic irregularity has a closer correlation with spectacle-corrected visual acuity than existing topographic indexes. Topographic irregularity is also an accurate predictor of spectacle-corrected visual acuity and may be a more sensitive tool for evaluating postoperative visual performance than current topographic measures.
Jules Stein Eye Institute and the Department of Ophthalmology, University of California, Los Angeles, School of Medicine, Los Angeles, California, USA.
J A
JA
Hovanesian
S S
SS
Shah
T
T
Onclinx
R K
RK
Maloney
D003315:Cornea / Q000503:physiopathology*; D019781:Corneal Topography; D016039:Corneal Transplantation; D005139:Eyeglasses; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D054018:Lasers, Excimer; D018903:Photorefractive Keratectomy; D011446:Prospective Studies; D012030:Refractive Errors / Q000503:physiopathology* / Q000628:therapy*; D054140:Refractive Surgical Procedures; D014792:Visual Acuity / Q000502:physiology*