Algorithm for Correcting the Keratometric Error in the Estimation of the Corneal Power in Eyes With Previous Myopic Laser Refractive Surgery

Abstract

The use of a single nk for estimating the corneal power in eyes that underwent a laser myopic refractive surgery can lead to significant errors. These errors can be minimized by using a variable nk dependent on r1c.

Clinical Validation of Adjusted Corneal Power in Patients with Previous Myopic Lasik Surgery

“…It should be considered that P c Gauss takes into account neither the curvature of the two corneal surfaces nor the corneal thickness. In this comparison, the mean difference between P k adj and P c Gauss was 0.14 ± 0.24 D ( p < 0.01), with a range of agreement from −0.33 to 0.60 D. There were only 4 cases out of 66 that showed differences between P k adj and P c Gauss of more than ±0.5 D. All these results are consistent with the theoretical predictions reported previously that estimated maximum differences between P k adj and P c Gauss of ±0.7 D [ 13 ]. Therefore, P k adj is an acceptable method for estimating the corneal power of corneas with previous myopic laser refractive surgery as 100% of estimations were within ±0.7 D if P c Gauss is taken as reference.…”

“…Furthermore, the results show that previously reported methods for this estimation are not better than the calculation of P k adj . We have confirmed the clinical prevalidation we conducted in 32 eyes that had undergone myopic LASIK surgery where no statistically significant differences between P k adj and TNP were found, with a mean difference value of 0.00 D and limits of agreement of −0.45 and +0.46 D [ 13 ].…”

“…Our research group recently proposed the use of a variable keratometric index ( n k adj ) for the estimation of the corneal power ( P c ) using the keratometric approach in patients with previous myopic LASIK surgery [ 13 ]. The following expression was defined for n k adj considering the ocular conditions of the Gullstrand eye model and the range of anterior and posterior curvature that is commonly found in this kind of patients [ 13 ]: where r 1 c is the postoperative anterior corneal radius.…”

“…For this reason, other methods that do not require patient's historical data have been developed [ 3 , 5 , 8 – 11 ]. In this line, our research group has recently proposed a new method for estimating with enough accuracy the corneal power using the keratometric approach that has been found to be valid in both healthy [ 12 ] and post-LASIK eyes [ 13 ]. This algorithm based on a variable keratometric index was named adjusted keratometric index ( n k adj ) and it has been prevalidated clinically in a sample of 32 eyes that had undergone previously myopic LASIK surgery [ 13 ].…”

“…In this line, our research group has recently proposed a new method for estimating with enough accuracy the corneal power using the keratometric approach that has been found to be valid in both healthy [ 12 ] and post-LASIK eyes [ 13 ]. This algorithm based on a variable keratometric index was named adjusted keratometric index ( n k adj ) and it has been prevalidated clinically in a sample of 32 eyes that had undergone previously myopic LASIK surgery [ 13 ]. The aim of the current study is to validate clinically this algorithm for the estimation of the corneal power in eyes with previous myopic LASIK in a larger population including also a larger range of intended refractive corrections.…”