Major variables used for grading keratoconus (MaxKm, MCT, HOARMS) can be linked by linear regression equations to predict the pathology's behavior.

Non-central keratoconus has lesser effect on SimK, pachymetry and smaller-aperture HOARMS. Using 'SimK steep >47.2 D or CCT < 491.6 μ' may miss timely referral for topography in many of these cases. Using more stringent criteria of SimK steep K ≥ 45.8 D or CCT ≤ 503 μ to get a corneal topography done to rule out keratoconus is recommended, especially in cohorts with higher risk.

Fellow eye symmetry is seen in illumination-governed centroid shifts and the post-flash re-dilatation response. The pupil dilates back briskly with a time-dependent cubic function, which is similar for fellow eyes in normal patients.

PurposeTo analyze single session, intrauser reliability of a Scheimpflug device for anterior chamber (AC) and corneal parameters.MethodsIn this observational study, 100 normal candidates underwent Scheimpflug analysis with Sirius 3D Rotating Scheimpflug Camera and Topography System (Costruzione Strumenti Oftalmici, Italy). Two scans in dark room conditions were performed by the same experienced user. The candidates were asked to keep both eyes closed for 5 min before the scans. Exclusion criteria were previous ocular surgery, corneal scarring and anterior segment/posterior segment anomalies. Only the right eyes were used for the analysis. Both corneal (central, minimum, and apical thickness, volume, horizontal visible iris diameter, and apical curvature) and anterior chamber (volume, depth, angle, horizontal diameter) measurements were evaluated.ResultsThere was no difference in the means of repeated measurements (p > 0.05, ANOVA). Intraclass correlations between the measures were high and ranged from 0.995–0.997 for corneal to 0.964–0.997 for anterior chamber (AC) parameters. The precision of repeatability measures (1.96 × Sw) was approximately 5 μ for the central and minimum corneal thickness, 8 μ for the apical corneal thickness, 0.06 mm for AC (anterior chamber) depth and less than 2° for the AC angle.ConclusionsSirius Scheimpflug system has high repeatability for both corneal and AC parameters in normal eyes.

The criteria used to define keratoconus progression were satisfactory when compared to inter-session reliability of corneal parameters. Because higher variability was noted at apex, its curvature repeatability cut-off may be raised to 1.25 D for identifying progressive keratoconus. [J Refract Surg. 2016;32(7):465-472.].