Intraocular lens power prediction in patients who undergo cataract surgery following previous radial keratotomy
W. A. Lyle and G. J. Jin
Eye Institute of Utah, Salt Lake City, USA.
BACKGROUND: Previous experience has shown that there is no technical
difficulty in performing cataract surgery on patients who have previously
undergone radial keratotomy. However, some researchers have reported
inaccuracy in intraocular lens (IOL) power selection. OBJECTIVES: To assess
the visual and refractive outcomes of our patients and to compare different
formulas and variables to improve accuracy in power determination. MAIN
OUTCOME MEASURES: Ten eyes subjected to phacoemulsification with in-the-bag
posterior chamber lens implantation 79 months (range, 36-118 months) after
radial keratotomy were evaluated in this study. The IOL power was
retrospectively calculated for each eye using the Binkhorst, SRK II, and
Holladay formulas with the current keratometry reading, the
refractive-derived keratometric value (K), the current refractive-derived
K, and the adjusted K. The final refractive result was used as a criterion
to judge the accuracy and predictability for each approach. RESULTS: Three
eyes underwent an IOL exchange after initial surgery. Among the 7 eyes that
did not undergo an IOL exchange, a hyperopic shift that regressed
approximately 3 months after surgery occurred in the early postoperative
period. At the final examination, 5 of the 7 eyes had a hyperopic error,
with 2 eyes showing more than 1.00 diopter (D). Overall, in an average of
27 months (range, 9-80 months) of follow-up, an uncorrected visual acuity
of 20/40 or better was obtained in 6 (60%) of the eyes. All 10 eyes had a
20/25 or better postoperative best-corrected visual acuity. The mean
(+/-SD) spherical equivalent refraction was changed from -0.78 +/- 3.49 D
preoperatively to 0.45 +/- 1.31 D postoperatively. We found that the
Binkhorst and Holladay formulas are more accurate than the SRK II formula.
With the use of an adjusted K (ie, the current average K minus 1.0 D) in
combination with the Binkhorst and Holladay formulas, most of the eyes
would achieve a refraction of -2.00 to +0.50 D. CONCLUSIONS: A corneal
flattening effect caused by cataract surgery tends to occur in eyes that
have undergone previous radial keratotomy. The use of an average between
the Binkhorst and Holladay formulas, aiming for -0.75 D with an adjusted K,
seems to be a more accurate and predictable method for IOL power
calculation. This approach could reduce the chance of postoperative
hyperopia.
