Abstract
Purpose:To determine the sensitivity and specificity of anterior and posterior corneal elevation parameters as determined by Orbscan II (Bausch and Lomb, Rochester, NY, USA) in discriminating between (sub) clinical keratoconus (KCN) and normal corneas.Methods:This prospective case-control study included 28 eyes with subclinical KCN, 65 with clinical KCN and 141 normal corneas. Anterior and posterior corneal elevation was measured and compared in the central 5-mm corneal zone using Orbscan II.Results:Receiver operating curves (ROC) curve analyses for posterior corneal elevation showed predictive accuracy in both KCN and subclinical KCN with an area under the curve (AUC) of 0.97 and 0.69, respectively while optimal cutoff points were 51 μm for KCN and 35 μm for subclinical KCN. These values were associated with sensitivity and specificity of 89.23% and 98.58%, respectively, for KCN; and 50.00% and 88.65% for subclinical KCN. ROC curve analyses for anterior corneal elevation showed predictive accuracy in both KCN and subclinical KCN with AUC of 0.97 and 0.69, respectively while optimal cutoff points were 19 μm for KCN and 16 μm for subclinical KCN. These values were associated with sensitivity and specificity of 93.85% and 97.16%, respectively, for KCN; and 60.71% and 87.94% for subclinical KCN.Conclusion:Anterior and posterior corneal elevation data obtained by Orbscan II can well discriminate between KCN and normal corneas, however the reliability of their indices is lower in differentiating subclinical KCN from normal cases.
Highlights
Keratoconus (KCN) is a bilateral, non‐inflammatory and usually progressive ectatic corneal disorder characterized by thinning and protrusion of the central cornea, leading to decreased vision as a result of myopia and irregularReceived: 10-05-2014Accepted: 22-06-2014 astigmatism.[1,2,3,4] Biomicroscopic examination and placido disk–based corneal topography are widely used methods for the diagnosis of KCN
Major criteria were the presence of Vogt’s striae and Fleischer ring of at least 2 mm detected by slit lamp, skewed radial axis (SRAX) index exceeding 20°, keratoconus prediction index (KPI) >0.3, keratoconus severity index (KSI) >30%, and keratoconus index (KCI) reported as an abnormal topographic pattern
Mean anterior corneal elevations in both KCN (49.35 ± 21.60 μm; P = 0.001) and subclinical KCN (15.07 ± 7.48 μm; P = 0.028) groups were significantly higher as compared to the normal group (11.05 ± 4.03 μm)
Summary
Keratoconus (KCN) is a bilateral, non‐inflammatory and usually progressive ectatic corneal disorder characterized by thinning and protrusion of the central cornea, leading to decreased vision as a result of myopia and irregular. Accepted: 22-06-2014 astigmatism.[1,2,3,4] Biomicroscopic examination and placido disk–based corneal topography are widely used methods for the diagnosis of KCN. Placido disk–based corneal topography is a highly sensitive and specific diagnostic tool, ; it only evaluates the anterior surface of Access this article online. With the advent of scanning slit topography and rotating Scheimpflug imaging, anterior and posterior corneal surface elevation measurements and curvature map detection became possible. Height data can directly assess protrusion; they differ from curvature map assessments of relative distortion of the cornea, and can provide useful diagnostic information in KCN. Current diagnostic concern in the management of KCN is detection of subclinical KCN which is critical prior to keratorefractive procedures considering the high prevalence of KCN among corneal refractive surgery candidates and the fact that the condition is the main cause of keratectasia after refractive surgeries.[4,5,6]
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