Revisiting keratoconus diagnosis and progression classification based on evaluation of corneal asymmetry indices, derived from Scheimpflug imaging in keratoconic and suspect cases

Abstract

PurposeTo survey the standard keratoconus grading scale (Pentacam®-derived Amsler–Krumeich stages) compared to corneal irregularity indices and best spectacle-corrected distance visual acuity (CDVA).Patients and methodsTwo-hundred and twelve keratoconus cases were evaluated for keratoconus grading, anterior surface irregularity indices (measured by Pentacam imaging), and subjective refraction (measured by CDVA). The correlations between CDVA, keratometry, and the Scheimpflug keratoconus grading and the seven anterior surface Pentacam-derived topometric indices – index of surface variance, index of vertical asymmetry, keratoconus index, central keratoconus index, index of height asymmetry, index of height decentration, and index of minimum radius of curvature – were analyzed using paired two-tailed t-tests, coefficient of determination (r2), and trendline linearity.ResultsThe average ± standard deviation CDVA (expressed decimally) was 0.626 ± 0.244 for all eyes (range 0.10–1.00). The average flat meridian keratometry was (K1) 46.7 ± 5.89 D; the average steep keratometry (K2) was 51.05 ± 6.59 D. The index of surface variance and the index of height decentration had the strongest correlation with topographic keratoconus grading (P < 0.001). CDVA and keratometry correlated poorly with keratoconus severity.ConclusionIt is reported here for the first time that the index of surface variance and the index of height decentration may be the most sensitive and specific criteria in the diagnosis, progression, and surgical follow-up of keratoconus. The classification proposed herein may present a novel benchmark in clinical work and future studies.

Evaluation of Visual Acuity, Pachymetry and Anterior-Surface Irregularity in Keratoconus and Crosslinking Intervention Follow-up in 737 Cases

“…142 eyes belonged to female patients and 233 to male patients. The noted preponderance in both groups toward male population is consistent with our clinical experience in male-female incidence in keratoconic patients, 8 and keratoconus incidence large studies. 14 Inclusion criteria for group B were uneventful Athens-protocol rehabilitation, and no other ocular complications.…”

“…These indices were: the (unitless) index of surface variance (ISV), an expression of corneal surface curvature irregularity, expressing the standard deviation of the sagittal radius values from the mean; and the index of height decentration (IHD), calculated with Fourier analysis of corneal height data to quantify the degree of vertical cone decentration. 8 The decentration is calculated on a ring of 3 mm radius. For groups A and C, measurements from the most recent clinical visit has been included in the study.…”

“…[2][3][4] Our long clinical experience with keratoconic screening and rehabilitation [5][6][7] indicates that neither corneal pachymetry nor visual acuity (uncorrected distance visual acuity, UDVA, and best-spectacle corrected distance visual acuity, CDVA) can be reliable indicators of ectasia and/or keratoconus progression assessment. 8 One may expect that the presence of large amounts of corneal irregularities might hamper sufficient spectacle-correction of visual acuity. However, at least in our experience, often enough keratoconic patients present with surprisingly high CDVA, even near 20/20, despite severe topographic irregularity and/or pachymetric thinning present.…”

Validation of rs2956540:G>C and rs3735520:G>A association with keratoconus in a population of European descent

“…1 Only patients with KC grade 1 or higher according to the Oculus topographic KC classification based on data obtained by Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany) were included. 10 Some eyes had advanced disease with typical signs such as Vogt striae, Fleischer ring and stromal scarring, but this was not an inclusion requirement for the purposes of this study. Bilaterally grafted patients for KC were also considered affected and thus included in the study.…”

Assessing Progression of Keratoconus and Cross-linking Efficacy: The Belin ABCD Progression Display

“…Others have used this system with various modification and additions in an attempt to better diagnosis or characterize the severity of disease. 21,22 …”