Intraocular lens power calculation in keratoconus; A review of literature

Abstract

Purpose To review the published literature regarding cataract surgery in keratoconus (KCN) patients with emphasis on challenges encountered during intraocular lens (IOL) power calculation and their solutions. Methods A literature review was performed to investigate all the relevant articles on the advancements of IOL calculations in KCN patients. Results Cataract surgery in keratoconic eyes can improve patients' refraction, and proper patient selection and IOL calculation methods are necessary to get the best results. The main problem in KCN patients is unreliable biometric measurements. It is more difficult to make conclusions in more advanced keratoconic corneas, as the steep keratometric values in these eyes will result in the selection of a low-power IOL. Presence of a low-power IOL will yield in extreme postoperative hyperopia, and IOL exchange might be mandatory. In cases in which keratoplasty may be needed in the future, contact lens fitting can help surgeons make a better decision preoperatively. Axial length (AL) measurements may have better repeatability and reproducibility than keratometry (K) readings in keratoconic eyes. SRK II formula may provide the most accurate IOL power in mild KCN. There is still not a comprehensive consensus of which formula is the best one in moderate and severe KCN, as the literature is limited in this subject. Conclusions Various methods of IOL power calculation optimization and recommendations may hold the key to improve surgical outcomes in keratoconic eyes. There are multiple sources of biometric error in KCN patients, hence IOL calculation methods may not be as efficient as expected in these eyes.

Repeatability and agreement of biometric measurements using spectral domain anterior segment optical coherence tomography and Scheimpflug tomography in keratoconus

“…Such patients present unique challenges for the cataract surgeon regarding intraocular lens (IOL) power calculation. The inherent difficulty in obtaining accurate biometric measurements, changes in the relationship between the anterior and posterior cornea, inaccurate calculation of the effective lens position due to inaccurate keratometry measurement, and axis of astigmatism [ 9 ] can result in unpredictable refractive outcomes [ 10 ]. Reduction of biometric measurement error can therefore optimize post-operative refractive and visual outcomes in patients with keratoconus.…”

Assessing the validity of corneal power estimation using conventional keratometry for intraocular lens power calculation in eyes with Fuch’s dystrophy undergoing Descemet membrane endothelial keratoplasty

“…Significant P values: bold; SD standard deviation, ΔD Total difference between predicted and measured total corneal power, ΔD P difference between predicted and measured postoperative posterior corneal power, n c fictitious keratometer index, R PA posterior to anterior corneal curvature radii ratio, R PPPA postoperative posterior to preoperative anterior corneal curvature radii ratio, Control control group data; FECD preoperative data of eyes with FECD, FECD/DMEK postoperative posterior and preoperative anterior corneal curvature data of eyes with FECD undergoing DMEK surgery This study focused on corneal power measurement that accounts for approximately two-thirds of the total dioptric power of the eye [17]. If the calculation of corneal power is inaccurate, it will have profound consequences on subsequent steps in the calculation of IOL power [18][19][20][21].…”

Comparative clinical accuracy analysis of the newly developed ZZ IOL and four existing IOL formulas for post-corneal refractive surgery eyes

“…Various factors can lead to corneal refractive power errors. First, traditional IOL power calculators, for normal or irregular cornea, use a fixed ratio to determine the posterior corneal refractive power, and different calculators have different fixed values [ 28 , 29 ]. Corneal refractive power bias will be positively correlated with the ratio bias, which is significant for an irregular cornea.…”