Comparison of Standard and Total Keratometry Astigmatism Measured with three Different Technologies

Abstract

Purpose: To compare the keratometric and total corneal astigmatism measures provided by three different technologies as well as to assess the level of interchangeability among them. Methods: A Prospective, comparative study enrolling 94 eyes from 53 patients (age, 29-77 years) was carried out. All participants were patients with the diagnosis of cataract or patients with a transparent crystalline lens but seeking surgical presbyopia correction. A complete eye examination was performed in all eyes, including corneal analysis with three different devices: IOL-Master 700 (Carl Zeiss Meditec), Cassini (i-Optics), and Pentacam (Oculus Optikgeräte GmbH). Interchangeability of standard and total keratometric readings (equivalent keratometric readings for Pentacam) and astigmatism measures with these three systems were evaluated with the Bland-Altman analysis. Results: Significantly higher standard and total keratometric readings were obtained with the IOL-Master compared to the other two systems (p<0.001). Likewise, a significantly higher magnitude of standard and total keratometric astigmatism was obtained with the Cassini system (p<0.001). Ranges of the agreement for corneal power measurements between devices varied from 0.58 D to 1.53 D, whereas they ranged from 0.46 D to 1.37 D for standard and total astigmatism measurements. Conclusion: Corneal power and astigmatism measures obtained with IOL-Master 700, Cassini, and Pentacam systems cannot be used interchangeably. The impact of these differences on the refractive predictability achieved with different types of intraocular lenses (IOL) should be evaluated in the future in order to define which is the best corneal evaluation approach for optimizing the IOL power calculations.

Measurements of Anterior and Posterior Corneal Curvatures with OCT and Scheimpflug Biometers in Patients with Low Total Corneal Astigmatism

“…The mean dioptric corneal power in our cohort was significantly lower for TCRP by 0.2 D in comparison to the TK value. These results are in agreement with other reports [ 5 , 6 ]. Therefore, for toric IOL calculations, significant differences can be expected, if real total corneal power values from different devices would be applied.…”

“…The TNP represents the optical power derived from sagittal curvatures of both corneal surfaces and correct refractive indices. Other authors consider equivalent keratometric readings, which are derived from corneal elevation values of the anterior and posterior surfaces in addition to local corneal thickness, as more appropriate for comparing Pentacam system with other devices [ 6 ]. The divergence in parameters chosen for comparisons shows clearly that there is no clinical gold standard for the total corneal astigmatism measures.…”

“…However, each device uses specific manufacturer’s algorithms to derive the radius from the measured raw data. Therefore, the results are often regarded as not interchangeable [ 5 , 6 , 7 , 8 ]. For anterior and posterior keratometry measurements, studies have shown significant differences between swept-source OCT (SS-OCT) and Scheimpflug devices [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ], which are considered clinically irrelevant [ 9 , 10 ] or relevant [ 5 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ], depending on interpretation.…”