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.
Hovanesian
J A
JA
Jules Stein Eye Institute and the Department of Ophthalmology, University of California, Los Angeles, School of Medicine, Los Angeles, California, USA.
Shah
S S
SS
Onclinx
T
T
Maloney
R K
RK
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*