Multiple published clinical studies have demonstrated that the Kane formula is more accurate than all currently available IOL formulas (including Hill-RBF 2.0, Barrett Universal 2, Olsen, Haigis, Hoffer Q, Holladay 1, SRK/T, EVO and Holladay 2).
- A single surgeon study of 846 patients was the first to show that the Kane formula was the most accurate formula (https://bmjophth.bmj.com/content/4/1/e000251).
- This finding was then confirmed in the two largest studies on IOL power formulas (with samples of 18,501 patients and 10,930 patients, respectively). These two landmark studies are available in Ophthalmology (https://www.aaojournal.org/article/S0161-6420(19)30284-2/fulltext) and the Journal of Cataract and Refractive Surgery (https://journals.lww.com/jcrs/Fulltext/2020/01000/Assessment_of_the_accuracy_of_new_and_updated.2).
The Kane formula maintains its accuracy at the extremes of axial length, resulting in a 25.1% reduction in absolute error in long eyes (≥26.0 mm), compared with the SRK/T; and a 25.5% reduction in absolute error in short eyes (≤22.0 mm), compared with the Hoffer Q formula.
In a recent study of extreme axial hyperopia, published in the Journal of Cataract and Refractive Surgery, the Kane formula resulted in an additional 22.0% of patients within ±0.50 D of the refractive aim compared with the Barrett Universal 2 and 23.1% more compared to the Hoffer Q. This study is available at the following link: https://journals.lww.com/jcrs/Abstract/9000/Intraocular_lens_formula_comparison_in_axial.99862.aspx
The Kane formula was developed in September 2017 using ~30,000 highly accurate cases. The formula is based on theoretical optics and incorporates both regression and artificial intelligence components to further refine its predictions. The formula was created using high-performance cloud-based computing which is a way to leverage the power of the cloud to create a virtual supercomputer capable of performing many decades worth of calculations in a few days. A focus of the formula was to reduce the errors seen at the extremes of the various ocular dimensions which is where the current formulas display larger errors. Variables used in the formula are axial length, keratometry, anterior chamber depth, lens thickness, central corneal thickness and patient biological sex.
The Kane toric formula uses an algorithm incorporating regression, theoretical optics and artificial intelligence techniques to calculate the total corneal astigmatism. It then applies an ELP based approach to calculate the residual astigmatism for a particular eye and IOL power combination. It is recommended to use an SIA of zero with the Kane toric formula when performing surgery with a temporal incision size of ≤2.75 mm.
In the largest study on toric IOL formula accuracy, the Kane toric formula has been shown to be more accurate than all currently available toric formulas (Barrett, Abulafia-Koch, Holladay 2 with total SIA, EVO 2.0 and Næser-Savini). This study is available in Ophthalmology (https://www.aaojournal.org/article/S0161-6420(20)30416-4/fulltext).
The Kane keratoconus formula is a purely theoretical modification of the original Kane formula. It uses a modified corneal power, derived from anterior corneal radii of curvature, that better represents the true anterior/posterior ratio in keratoconic eyes. The formula also minimizes the effect of corneal power on the ELP calculation to enable more accurate predictions. There is no requirement for additional variables for the keratoconus formula and the formula works with the same A-constant used for non-keratoconic patients. A myopic target refraction is recommended in patients with an average corneal power >48 D. Between 48 D and 53 D, a target of -0.50 DS is recommended; between 53 D and 59 D, a target of -1.00 DS is recommended; and above 59 D, a target of -1.50 to -2.50 DS is recommended. These targets are designed to avoid an undesirable hyperopic outcome.
The Kane keratoconus formula was shown to be significantly more accurate than all currently available formulas in patients with keratoconus in a study recently published in Ophthalmology (https://www.aaojournal.org/article/S0161-6420(20)30166-4/fulltext).
Compulsory fields for the calculator are the A-constant, biological sex, axial length, corneal power and anterior chamber depth. Although adding lens thickness and central corneal thickness improves the prediction, they are optional variables. This allows owners of older biometers to use the formula.
Index relates to the K-index of the instrument used to measure the corneal curvature. A default value of 1.3375 has been selected. If your device uses a different K-index, please select the appropriate option from the drop-down menu.
The formula has been developed to have an A-constant very similar to the SRK/T A-constant. If the surgeon has an optimised A-constant, then that is recommended for use. Otherwise, we recommend the ULIB SRK/T A-constant for any particular IOL. The “Constants” page has information about the appropriate constant for different IOLs.