Differences in central and non‐central keratoconus, and their effect on the objective screening thresholds for keratoconus

Abstract

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.

Keratoconus Detection Based on a New Corneal Volumetric Analysis

“…In spite of all this previous experience showing the reduction of corneal volume in keratoconus, there are no studies reporting a moderate predictive ability of this parameter for detecting this pathological condition 6 . Likewise, although topographic, pachymetric and aberrometric parameters have been shown to be useful for keratoconus detection 4 , they are not sensible enough for detecting early central keratoconus 24 . Indeed, it has been demonstrated that more stringent diagnostic criteria are required for topographic and pachymetric criteria to avoid missing pathological cases, but with the consequent reduction in specificity 24 .…”

“…Likewise, although topographic, pachymetric and aberrometric parameters have been shown to be useful for keratoconus detection 4 , they are not sensible enough for detecting early central keratoconus 24 . Indeed, it has been demonstrated that more stringent diagnostic criteria are required for topographic and pachymetric criteria to avoid missing pathological cases, but with the consequent reduction in specificity 24 . Considering that the correlation between corneal volume changes and aberrations increased with increase in the severity of the disease, we decided to obtain a predicting model by logistic regression for the detection of incipient keratoconus (grade I) based on the combination of corneal volume and corneal aberrometric data.…”

“…It should be considered that this system uses anterior and posterior topographic asymmetries, corneal aberrometric data and the points of minimal corneal thickness to perform its predictions 16 . Concerning the sample used, the inclusion of a significant sample of central keratoconus may have led to some missing pathological cases as they do not present geometric symmetries and high levels of coma aberration 24 . For this reason, the inclusion of the reduction of the corneal volume should be a crucial factor to be included in predictive models, as demonstrated in the current study.…”

Effect of Conus Eccentricity on Visual Outcomes After Intracorneal Ring Segments Implantation in Keratoconus

“…Central cones have higher simulated keratometry values at 3 mm and anterior corneal higher order aberrations compared to peripheral cones. 27 It has also been documented that the pericentral cornea flattens more than the central cornea after ICRS implantation, thereby maintaining the prolate shape of the corneal optical zone. 28,29 Shetty et al 30 showed that cone location appears to affect visual acuity after combined topography-guided photorefractive keratectomy and corneal cross-linking, with better results for cones within a central 2-mm zone.…”

Nationwide reduction in the number of corneal transplantations for keratoconus following the implementation of cross‐linking

“…Keratoconus is a corneal disease characterized by a gradual thinning of the central and peripheral corneal stroma, resulting in corneal protrusion and reduced visual acuity (Rabinowitz 1998;Prakash et al 2016). Optical correction with either rigid contact lenses or spectacles is usually sufficient to counteract the reduced visual acuity in mild cases of keratoconus.…”