Evaluating progression in keratoconus: are our numerical indicators for cross-linking reliable enough?

Session Details

Session Title: Imaging I

Session Date/Time: Monday 12/09/2016 | 14:30-16:30

Paper Time: 15:30

Venue: Hall C2

First Author: : G.Prakash UNITED ARAB EMIRATES

Co Author(s): :    R. Philip   R. Bacero   D. Srivastava              

Abstract Details

Purpose:

To evaluate the robustness of numerical indications of corneal cross linking by evaluating the intersession reliability of recently used parameters of progression in keratoconus.

Setting:

NMC Specialty Hospital, United Arab Emirates

Methods:

In this observational study, 100 eyes of 100 patients with keratoconus underwent analysis with Sirius Scheimpflug Topography System (CSO, Italy) by a single user. Two sessions (3 scans per session) were performed 2- 4 weeks apart. Cases having poor quality scans, recent visual deterioration, and ocular surgery were excluded. The corneal variables measured were thinnest point and apex characteristics (pachymetry, polar-coordinates), volume, central simulated keratometry, central corneal thickness, maximum elevation (anterior, posterior), symmetry indices (front, back) and Baiocchi-Calossi-Versaci(BCV) index. Intra-session (first session, all three measurements) and inter-session (one measurement from each session, selected randomly) statistics were computed.

Results:

There was no difference in the six measurements for all the variables (p>0.05, ANOVA). The intra- and inter-session intraclass correlations were high (0.937-0.997) and within-subject standard deviation (Sw) were satisfactory (<5µ for thickness, <0.5D for curvature, and <0.11mm, <5˚ for polar coordinates). Inter-session-Repeatability (2.77xSw) was found to be satisfactory when compared to previously used central keratometric (>1.0D increase) or pachymetric (>2%/>5% decrease) guidelines to define progression. Apex power repeatability (1.24D) was found to be poorer than previously used recommendation (1D change).

Conclusions:

Our finding suggest that an increase in central keratometry of 1D or apex keratometry of 1.5D, and decrease of 10 microns for corneal thickness is more than the inter-session repeatability in keratoconus, and thus could be used as guidelines for suggesting progression. However, it is prudent to use a combination of these parameters and not to rely on single factor .The criteria used in previous studies to define keratoconus progression were satisfactory when compared to intersession reliability of corneal parameters. As higher variability was noted at apex, its curvature-cutoff may be raised to 1.25D.

Financial Disclosure:

NONE