Preliminary validation of an optimized algorithm for intraocular lens power calculation in keratoconus

Abstract

Purpose:This study aimed to evaluate the theoretical influence on intraocular lens power (PIOL) calculation of the use of keratometric approach for corneal power (Pc) calculation in keratoconus and to develop and validate an algorithm preliminarily to minimize this influence.Methods:Pc was calculated theoretically with the classical keratometric approach, the Gaussian equation, and the keratometric approach using a variable keratometric index (nkadj) dependent on r1c(Pkadj). Differences in PIOL calculations (ΔPIOL) using keratometric and Gaussian Pc values were evaluated. Preliminary clinical validation of a PIOL algorithm using Pkadj was performed in 13 keratoconus eyes.Results:PIOL underestimation was present if Pc was overestimated, and vice versa. Theoretical PIOL overestimation up to −5.6 D and −6.2 D using Le Grand and Gullstrand eye models was found for a keratometric index of 1.3375. If nkadj was used, maximal Δ PIOL was ±1.1 D, with most of the values ≤±0.6 D. Clinically, PIOL under- and over-estimations ranged from −1.1 to − 0.4 D. No statistically significant differences were found between PIOL obtained with Pkadj and Gaussian equation (P > 0.05).Conclusion:The use of the keratometric Pc for PIOL calculations in keratoconus can lead to significant errors that may be minimized using a Pkadj approach.

Cataract surgery in patients with underlying keratoconus: focused review

“…4,19,25 Importantly, the ratio between anterior and posterior corneal curvature is altered in patients with KC. [26][27][28][29][30][31][32] Thus, conventional keratometry (K)-which only takes into account the radius of the anterior curvature of the cornea and assumes a standard K index of 1.3375 based on the Gullstrand schematic eye model-may not adequately account for the influence of the posterior cornea and can frequently result in overestimation of corneal power in KC patients. 4,19,[26][27][28][29][30][31][32] Furthermore, according to some authors, tear film irregularities commonly exist in KC, therefore making measurements of corneal curvature less repeatable.…”

“…[26][27][28][29][30][31][32] Thus, conventional keratometry (K)-which only takes into account the radius of the anterior curvature of the cornea and assumes a standard K index of 1.3375 based on the Gullstrand schematic eye model-may not adequately account for the influence of the posterior cornea and can frequently result in overestimation of corneal power in KC patients. 4,19,[26][27][28][29][30][31][32] Furthermore, according to some authors, tear film irregularities commonly exist in KC, therefore making measurements of corneal curvature less repeatable. 19,33 Some evidence suggests that modern elevation-based topography devices (such as the Pentacam and the Scheimpflug pachymeter) may help mitigate erroneous corneal power measurement by taking the posterior curvature of the cornea into account.…”

Central corneal thickness and its determinants in a geriatric population: a population-based study

“…The CCT is also an influential factor in intraocular pressure measurement (IOP) and serves as a predictor in the progression of ocular hypertension (HTN) to primary openangle glaucoma [3]. In cataract surgery, CCT measurement is important in some intraocular lens (IOL) power calculation formulas, especially in patients with a history of refractive surgery and also a history of KCN or other corneal abnormalities [4,5].…”

Optical models for intraocular lens planning in keratoconus: A step in the right direction and more to do

“…This issue of Indian Journal of Ophthalmology carries an interesting article titled, “Preliminary Validation of an Optimized Algorithm for Intraocular Lens Power Calculation in Keratoconus.”[ 1 ] The paper presents highly descriptive analyses of different parameters that can impact the calculation of intraocular lens (IOL) power using two different eye models. Such studies assist in truly understanding the relative impact of each selection parameter such as anterior corneal radius and posterior corneal radius.…”

“…Currently, there is very limited data available. If the authors of the study[ 1 ] test their model prospectively in diseases, it will fully demonstrate the accuracy of their model.…”