Validity of the keratometric index: Large population-based study

Abstract

Modifying the keratometric index increased the accuracy of predicting the posterior corneal power.

Clinical validation of an algorithm to correct the error in the keratometric estimation of corneal power in normal eyes

“…1 Corneal power overestimation was always found in both eye models when an n k value of 1.3375 was used. These findings 1 and those in previous studies [2][3][4] show there is a need for a precise model to determine the most appropriate n k value for calculating P c with the keratometric approach. We developed and reported a fast, easy, and clinically applicable method for determining the most appropriate n k for the keratometric estimation in each specific case.…”

“…[2][3][4]9,11 The classic n k value of 1.3375 was proposed for convenience rather than for optical significance because it provided an agreement between a specific value of the anterior radius of curvature and the total P c (7.5 mm and 45.0 D). 10 Other n k values have been derived from schematic eye models, such as the value of 1.3315, which was derived from the Gullstrand schematic eye and recommended by Olsen.…”

“…All these approaches attempted to minimize the difference between the keratometric and Gaussian corneal power (DP c ) using a single n k value with the SD or range as a general solution. However, differences between keratometric and Gaussian powers have been reported despite the use of some of the proposed n k values; some differences were higher than 1.0 D. 3,4 One factor accounting for this is the incorrect assumption of a constant and linear relationship 1,4,5 between the curvature of the anterior and the posterior corneal surface. The k ratio, which is defined as the ratio of r 1c to r 2c , is not constant in the range of curvatures of the normal healthy cornea, which range from 1.157 to 1.295.…”

Comparison of corneal astigmatism and axis location in cataract patients measured by total corneal power, automated keratometry, and simulated keratometry

“…Hence, the TCP in this study gave higher astigmatism measurements than automated K or simulated K, which did not measure the posterior cornea. The use of a single keratometric index to compensate for posterior cornea might not reflect the true corneal astigmatism in all age groups 26,27 because the result might be different between ages. Furthermore, an earlier study 28 found a statistically significant difference in the amount of astigmatism between men (1.01 D) and women (1.06 D).…”

Effect of corneal aberrations on intraocular lens power calculations

“…One is the approximation related to the equivalent refractive index. 35 Although the value chosen for the model was equivalent to that predicted by physiological measurements, 31 a fully customized model could be used that considers the posterior corneal surface, although the impact of introducing further experimental measurement errors should be evaluated. In addition, IOL placement prediction remains a challenge.…”