Intraocular lens power calculation after corneal refractive surgery

Abstract

Purpose: To report refractive outcomes following phacoemulsification (PE) and posterior chamber intraocular lens (PCIOL) implantation in eyes with previous corneal refractive surgery. Methods: In this retrospective comparative study, 18 consecutive eyes of 14 patients with previous keratorefractive surgery for myopia including photorefractive keratectomy (PRK, 6 eyes; 33.3%) and laser in situ keratomileusis (LASIK, 12 eyes; 66.7%) underwent PE+PCIOL. Computerized corneal topography was employed to determine the flattest keratometric reading within the 3-mm central zone. This value was inserted into the Sanders-Retzlaff-Kraff/T (SRK/T) formula to calculate IOL power. IOL power selected for implantation was 1 D greater than the calculated value described above. Results: Mean age and follow-up period were 54.1±11.5 years and 29.9±26.3 months, respectively. Mean implanted lens power was 18.56±3.86 D which was not significantly different from mean back-calculated IOL power for target refraction (19.04±4.16 D) (P=0.28). There was no significant difference between mean target refraction (-0.94±0.52 D) and achieved postoperative spherical equivalent refractive error (-0.62±1.06) at final follow-up (P=0.28). The achieved spherical equivalent refractive error was within ±0.50 D of intended refraction in 8 (44.4%) eyes, within ±1.0 D in 11 (61.1%) eyes, and within ±2.0 D in 16 (88.9%) eyes. In a subgroup of patients (5 eyes) with complete pre-refractive surgery data, the difference between post-refractive surgery keratometry method and all other methods (P=0.02) and between the current method and the Feiz-Mannis method (P=0.01) was statistically significant. Conclusion:The method suggested herein is simple and independent of pre-refractive surgery data with results comparable to other commonly used methods.

Determining corneal power using Orbscan II videokeratography for intraocular lens calculation after excimer laser surgery for myopia

“…For these reasons, manual keratometry is inaccurate in estimating corneal power in eyes that have had laser refractive surgery. [2][3][4][5][6][7][8][9][10][11] Computerized videokeratography is based on computer analysis of Placido disk images projected onto the corneal surface. Computerized videokeratography measures more than 5000 points over the entire cornea and more than 1000 points within the central 3.0 mm.…”

“…Although these instruments offer good accuracy when applied to healthy, unoperated corneas with regular astigmatism, their use in measuring corneal power in patients with irregular astigmatism 1 or who have had keratorefractive surgery [2][3][4][5][6][7][8][9][10][11][12] can lead to significant residual postoperative refractive errors. These ''surprises'' stem partly from the fact that the manual keratometer averages measurements from only 4 discrete paracentral points on the anterior cornea and that it assumes a spherical central cornea, with the posterior cornea having a radius of curvature 1.2 mm smaller than its anterior counterpart.…”

“…14,15 The literature is replete with strategies to better determine corneal power in eyes that have had refractive surgery including photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). Among the most commonly used methods are refraction-based calculations, [3][4][5][6][7][8][9][10][11][16][17][18][19] rigid gas-permeable contact lens (RGP) overrefraction, 1,3,8,10,11,17,18,20 and computerized videokeratography (CVK). [1][2][3][4]6,[9][10][11]14,16,18,[21][22][23][24][25][26] The latter 2 techniques become particularly important when the preoperative refractive surgical history is unavailable.…”

Pseudoaccommodating bifocal intraocular lens implantation in eyes with previous corneal refractive surgery - refractive outcomes: case series of 8 eyes

“…Intraocular lens power calculations in eyes that have had previous myopic refractive surgery underestimate the IOL power for emmetropia, resulting in a high incidence of unintentional postoperative hyperopia, because of altered corneal geometry. Conversely, after laser refractive surgery for hyperopia, this could result in underestimation of keratometric readings, overestimation of the IOL power required, and myopic outcomes after phacoemulsification (3) . Techniques bypassing corneal power and axial length measurements were recently described.…”

“…Previous corneal refractive surgery has gained increasingly interest due to the number of patients willing to keep their spectacle or contact lenses independence, in spite of their presbyopia or age-related cataract (1,2) . Bifocal IOL implantation in these patients may be a challenging issue, because of inaccurate biometric calculations by standard formulas, what often leads to inappropriate lens power selection and higher incidence of unintentional residual ametropia (3) . Photic phenomena, inherent both to corneal refractive surgery and to bifocal IOLs, also raise concerns about visual outcomes in these patients.…”