Comparison of the corneal curvatures obtained from three different keratometers

Abstract

Introduction: Keratometry forms an important component of the biometry for a calculation of the intraocular lens power and selecting a contact lens’ parameters.

Objective: To investigate the agreement between three different keratometers commonly used in an ophthalmology clinic.

Materials and methods: In this prospective study, keratometry was performed using an IOL Master (IM), a manual keratometer (Man) and a autokeratometer (Top) in twenty five eyes of thirteen volunteer subjects. The average keratometry values and corneal astigmatism (J₁₈₀ and J₄₅ components) were computed and compared. The agreements between the instruments were analysed using the Bland Altman statistical method. The main outcome measures are average keratometry values and corneal astigmatism.

Results: The mean of average keratometry values obtained from the IOL Master, manual keratometry and autokeratometry were 44.388 ± 1.430, 44.297 ± 1.425 and 44.220 ± 1.497 D, respectively. The mean difference in the average keratometry between the instruments were 0.31 ± 0.09 for IM and Man (p = 0.012), 0.14 ± 0.17 for IM and Top (p = < 0.001) and 0.29 ± 0.77 for Man and Top (p = 0.26). The mean differences in the J₁₈₀ component of astigmatism were: 0.02 ± 0.11 for IM and Man, 0.02 ± 0.09 for IM and Top, and - 0.01 ± 0.11 for Man and Top. Similarly, for the J₄₅ component, the mean differences were 0.02 ± 0.12 for IM and Man, 0.01 ± 0.13 for IM and Top and - 0.02 ± 0.10 for Man and Top.

Conclusion: Average keratometry values obtained from different instruments vary significantly. The IOL Master consistently over-estimated the corneal power compared to the manual and the autokeratometer. All three instruments provided similar estimation of the corneal astigmatism.

Nepal J Ophthalmol 2013; 5(9):9-15

DOI: http://dx.doi.org/10.3126/nepjoph.v5i1.7815