Effects of Non-invasive Keratograph Break-Up Time on the Repeatability of Keratometry Measurements

Purpose: To evaluate the effects of the non-invasive keratograph break-up time on the repeatability of keratometric measurements derived using the Keratograph 5M in patients with dry eye syndrome.Methods: Thirty-six patients with dry eye and 30 controls were enrolled. We measured keratometric values twice in all subjects and explored whether the two measurements differed by more than 0.5 diopter (D) (the absolute value). We also evaluated the relationship between the absolute difference and the non-invasive keratograph break-up time (NIKBUT).Results: The intraclass correlation coefficients for astigmatism, flat keratometry (K), steep K, and mean K were all higher than 0.95 in patients, thus lower than in controls. The proportion of eyes with absolute differences over 0.5 D between the two keratometric values differed significantly between the dry eye and control groups in terms of the flat K and Kmax values (p = 0.033, 0.037). The average NIKBUT was negatively correlated with the absolute differences in Kmax and astigmatism (p = 0.030, R2 = 0.134 and p = 0.017, R2 = 0.160).Conclusions: In patients with dry eye syndrome, keratometric measurements are reliably repeatable, but slightly less so than in normal controls. The proportions of eyes exhibiting absolute keratometric differences over 0.5 D (two measurements) differed in the dry eye and control groups. The lower the non-invasive keratograph break-up time, the poorer the repeatability of keratometric measurements in the dry eye group. Therefore, care is required when obtaining keratometric values for such patients.