• Novel Metric to Estimate IOP in Patients With Soft Corneas

    By Lynda Seminara
    Selected By: Deepak P. Edward, MD

    Journal Highlights

    Journal of Cataract & Refractive Surgery
    2019;45(9):1316-1323

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    It can be difficult to obtain accurate intraocular pressure (IOP) readings in soft corneas, including those with keratoconus. In a large multicenter study, Chen et al. introduced a new metric—biomechanically corrected IOP (bIOP) for measuring IOP in the presence of soft corneas (bIOPs). Their algorithm appears to be highly accurate for this purpose.

    This retrospective case series was conducted in Italy and Brazil. The authors performed numeric analysis based on the finite element method to simulate the effect of tonometric air pressure of the Corvis ST dynamic Scheimpflug analyzer on eye globes that varied by thickness, geometry, and tissue. They then used these numeric predictions of ocular behavior to develop their algorithm.

    The bIOPs predictions were evaluated in keratoconic eyes, and these predictions were compared with those of the previously developed bIOP algorithm devised for normal healthy eyes. The main outcome was the absence of a significant difference in IOP between healthy eyes and keratoconic eyes when using the bIOP and bIOPs algorithms, respectively.

    Results were similar for the Italian and Brazilian datasets. Central corneal thickness was substantially greater in normal eyes. Although mean bIOP in normal eyes was comparable to that in keratoconic eyes, the mean uncorrected IOP with the Scheimpflug device was significantly lower in keratoconic eyes (p < .001). Moreover, for keratoconic eyes, bIOP values differed significantly from IOP values of the Scheimpflug analyzer (p < .001); differences were not significant for normal eyes. Moreover, bIOPs predictions were significantly less affected by corneal thickness and patient age than were IOP estimates from the Scheimpflug device.

    The authors aimed to separate the effects of corneal mechanical stiffness from those of IOP in the measurement process to provide a better representation of IOP than can be attained by traditional analyzers. Overall, they said, bIOPs may have potential application in progressive keratoconus if its predictions prove accurate in such cases. Investigation in progressive keratoconus also may settle the debate about whether IOP is higher in this subset of keratoconic eyes.

    The original article can be found here.