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Enhanced sensitivity to detect very early abnormalities in very asymmetric Keratoconus
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  1. Enhanced sensitivity to detect very early abnormalities in very asymmetric Keratoconus e-Poster P186 Marcella Q. Salomão, MD; Renato Ambrósio Jr., MD, PhD; Leonardo N. Pimentel; Isaac Ramos; Bruno Valbon; Ana Laura C. Canedo. Dr. Ambrósio is consultant for Oculus Optikgeräte GmbH (Wetzlar, Germany)

  2. Introduction • Keratoconus (KC) is a non-inflammatory, usually bilateral, progressive corneal degeneration, in which the corneal shape distorts, with progressive stromal thinning and ectasia. • A small percentage of cases present with a very asymmetric pattern. In some cases, the asymmetry can be so significant that the contra-lateral eye presents with normal anterior curvature (axial) maps. • A bilateral presentation as in these “normal” eyes may occur and could even be the explanation for many cases of ectasia after LASIK with no identifiable pre-operative risk factors. • Identifying asymptomatic cases with normal slit lamp exam, good spectacle corrected visual acuity, and normal corneal topography is critical; not only for screening of refractive surgery candidates, but to allow an enhanced treatment choice. e-Poster P186

  3. Purpose To investigate the efficacy of combined tomographic and biomechanical indices to detect very mild ectatic abnormalities or ectasia susceptibility in cases with proven form fruste keratoconus. Methods • Retrospective study • 23 “topographically normal” eyes with no diagnosis of keratoconus (KC) or keratoconus suspect (KCS) by the Nidek Corneal Navigator System using the Magellan Placido’s Corneal Topographer, from 23 patients who had clinical diagnosis of keratoconus only in the fellow eye. e-Poster P186 Red= KC Eye Green = Fellow Eye“topographically normal” (Forme FrusteKC) *BuscemiPM. Nidek corneal navigator software for topographic analysis of corneal states. J Refract Surg. 2004;20(5 Suppl):S747-50.

  4. Placido’sTopography -both eyes of 23 very asymmetric Keratoconus (Axial Maps, Smolek-Klyce Absolute Scale) e-Poster P186

  5. Belin/Ambrósio Enhanced Ectasia Display (BAD) Belin’s Enhanced Reference Surface e-Poster P186 Elevation maps considering the standard BFS were subtracted from the elevation maps with the enhanced BFS; and the highest difference between the maps in the central 4mm area was noted for anterior and posterior corneal surfaces. The differential map contains only 3 colors, each one corresponding to the amount of elevation change that occurs when moving between the standard and enhanced maps. Anterior - green is anything < 6, yellow is between 6 - 12, red is > 12 Posterior: green is anything < 8, yellow is between 8 - 20, red is > 20 Yellow and red maps were considered abnormal.

  6. Belin/Ambrósio Enhanced Ectasia Display (BAD) Clinical example Maguellan OS Pentacam OD Pentacam OS Maguellan OD e-Poster P186 BAD OD

  7. Belin/Ambrósio Enhanced Ectasia Display (BAD) Ambrosio’s Pachymetric Distribution The Corneal Thickness Spatial Profile (CTSP) represents the averages of thickness values of the points on 22 imaginary circles centered on the thinnest point with increased diameters at 0.4 mm steps. The Percentage of increase in thickness (PTI) starting from the thinnest point is also calculated. The calculated values are displayed in a progression graph, starting on the thinnest point, as the CTSP and PTI lines. Data from a 95% confidence interval of a normal population is also displayed, so that the clinician can compare the profile of each eye to a normal population. Abnormally thin corneas (ectatic) usually show abrupt and abnormal profiles, out of the 95% CI. e-Poster P186 Pachymetric Progression Index (PPI) for Minimal, Maximal and Average of all hemi-meridians were noted. Ambrósio’s Relational Thickness (ART) is the thinnest point (TP) divided by PPI (Ave, Max). Belin-Ambrósio deviation (BAD) combined index (D) from the deviation of normality of the front (dF) and back (dB) enhanced elevation, pachymetric progression (dP), thinnest value (dT) and vertical displacement (dY) were obtained from Pentacam.

  8. Corneal Biomechanics with ORA (Ocular Response Analyzer) • Corneal response to a collimetric air pulse is monitored by the infrared light reflection (applanation => peak) • It detects two applanation events correlated with the air pulse pressure (INWARD- p1 and OUTWARD- p2) • The delay of p2 is caused by corneal viscous damping • [CH = p1 – p2] and [CRF = p1 - (K * p2)] • Normal Values: CH: 10.17 ± 1.82 (range 3.23 to 14.58) • CRF: 10.14 ± 1.8 (range 5.45 to 15.1) • Ectasia leads to lower CH and CRF and altered signals • CH or CRF < 8.8mmHg is considered a relative contra • indication for LASIK based on normal population values • Advanced ORA signal analysis are under study e-Poster P186

  9. Results • All cases were detected by at least two parameters. • All parameters (5Ds) were significantly different in the FFKC as compared to the Normal group (Mann–Whitney–Wilcoxon test, p<0.05). • Area under the ROC curve (AUROC) for the final Belin/Ambrósio deviation index (D) was 0.976 e-Poster P186 n=174 n=23 n=23

  10. Results • Areas under the ROC curves (AUROC) for ART-Ave and ART-Max were 0.942 and 0.957 • Best cut-off values were 1.27 (D), 512 (ART-Ave) and 391 (ART-Max) e-Poster n=23 • ART-Max had the highest sensitivity for detecting ectasia susceptibility (21 from 23 cases [91%] were lower than 400 microns) • The 2 cases with ART-Max of 440 and 481 had CH and/or CRF lower than 8.8mmHg and low peaks on the ORA waveform.

  11. Conclusions • Identification of ectatic corneas is critical because this is the most important risk factor for Iatrogenic keratectasia (along with CCT, ablation depth, age, residual stromal bed and multiple treatments). • Placido’s Topography (surface curvature map) enables the detection of sub-clinical (forme fruste) KC and PMD in eyes with normal slit lamp exam and good BSCVA, but… • There are cases with ectatic progression with normal topography and no other risk factors; and such cases illustrate the NEED for improving of identifying corneas at risk for ectasia (ECTASIA SUSCEPTIBILITY). • Corneal Ectasia is a bilateral disease, characterized by progressive corneal thinning and protrusion, due to an abnormal corneal structure. Thereby, corneal ToMography (CTm) and biomechanical tests are likely more sensitive and specific. • 3D Corneal ToMography provides further details beyond the surface, and CTm- derived parameters allows for the diagnosis of very mild forms of ectasia and its predisposition. • Enhanced ectasia screening successfully identified very mild forms of ectasia undetected by a Placido-based neural network artificial intelligence system based on front curvature data. Therefore, these new parameters increased sensitivity and specificity for the screening process and should be part of the refractive surgery candidates screening. e-Poster P186