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SD-OCT analysis of regional epithelial thickness profiles in keratoconus, postoperative corneal ectasia, and normal eyes.

ABSTRACT: To assess corneal microarchitecture and regional epithelial thickness profile in eyes with keratoconus, postoperative corneal ectasia (ectasia), and normal unoperated eyes (controls) using spectral-domain optical coherence tomography (SD-OCT).Regional corneal epithelial thickness profiles were measured with anterior segment SD-OCT (Optovue RTVue-100, Optovue Inc., Fremont, CA). Epithelial thickness was assessed at 21 points, 0.5 mm apart, across the central 6-mm of the corneal apex in the horizontal and vertical meridians.One hundred twenty eyes were evaluated, including 49 eyes from 29 patients with keratoconus, 32 eyes from 16 patients with ectasia, and 39 eyes from 21 control patients. Average epithelial thickness at the corneal apex was 41.18 ± 6.47 ?m (range: 30 to 51 ?m) for keratoconus, 46.5 ± 6.72 ?m for ectasia (range: 34 to 60 ?m), and 50.45 ± 3.92 ?m for controls (range: 42 to 55 ?m). Apical epithelial thickness was significantly thinner in eyes with keratoconus (P < .0001) and ectasia (P = .0007) than in controls. Epithelial thickness ranges in all other areas varied widely for keratoconus (range: 21 to 101 ?m) and ectasia (range: 30 to 82 ?m) compared to controls (range: 43 to 64) (P = .0063).SD-OCT demonstrated significant central and regional epithelial thickness profile differences between keratoconus, ectasia, and control eyes, with significant variability and unpredictability in ectatic eyes. This regional irregularity may necessitate direct epithelial thickness measurement for treatments where underlying stromal variations may be clinically relevant, including corneal collagen cross-linking or topography-guided ablations.

SUBMITTER: Rocha KM

PROVIDER: S-EPMC4123636 | biostudies-literature | 2013 Mar

REPOSITORIES: biostudies-literature

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SD-OCT analysis of regional epithelial thickness profiles in keratoconus, postoperative corneal ectasia, and normal eyes.

Rocha Karolinne Maia KM Perez-Straziota Claudia E CE Stulting R Doyle RD Randleman J Bradley JB

Journal of refractive surgery (Thorofare, N.J. : 1995) 20130301 3

<h4>Purpose</h4>To assess corneal microarchitecture and regional epithelial thickness profile in eyes with keratoconus, postoperative corneal ectasia (ectasia), and normal unoperated eyes (controls) using spectral-domain optical coherence tomography (SD-OCT).<h4>Methods</h4>Regional corneal epithelial thickness profiles were measured with anterior segment SD-OCT (Optovue RTVue-100, Optovue Inc., Fremont, CA). Epithelial thickness was assessed at 21 points, 0.5 mm apart, across the central 6-mm o ...[more]

PMID: 23446013

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Project description:ObjectiveTo map the corneal epithelial thickness with Fourier-domain optical coherence tomography (OCT) and to develop epithelial thickness-based variables for keratoconus detection.DesignCross-sectional observational study.ParticipantsOne hundred forty-five eyes from 76 normal subjects and 35 keratoconic eyes from 22 patients.MethodsA 26,000-Hz Fourier-domain OCT system with 5-?m axial resolution was used. The cornea was imaged with a Pachymetry + Cpwr scan pattern (6-mm scan diameter, 8 radials, 1024 axial-scans each, repeated 5 times) centered on the pupil. Three scans were obtained at a single visit in a prospective study. A computer algorithm was developed to map the corneal epithelial thickness automatically. Zonal epithelial thicknesses and 5 diagnostic variables, including minimum, superior-inferior (S-I), minimum-maximum (MIN-MAX), map standard deviation (MSD), and pattern standard deviation (PSD), were calculated. Repeatability of the measurements was assessed by the pooled standard deviation. The area under the receiver operating characteristic curve (AUC) was used to evaluate diagnostic accuracy.Main outcome measuresDescriptive statistics, repeatability, and AUC of the zonal epithelial thickness and diagnostic variables.ResultsThe central, superior, and inferior epithelial thickness averages were 52.3 ± 3.6 ?m, 49.6 ± 3.5 ?m, and 51.2 ± 3.4 ?m in normal eyes and 51.9 ± 5.3 ?m, 51.2 ± 4.2 ?m, and 49.1 ± 4.3 ?m in keratoconic eyes. Compared with normal eyes, keratoconic eyes had significantly lower inferior (P = 0.03) and minimum (P<0.0001) corneal epithelial thickness, greater S-I (P = 0.013), more negative MIN-MAX (P<0.0001), greater MSD (P<0.0001), and larger PSD (P<0.0001). The repeatability of the zonal average, minimum, S-I, and MIN-MAX epithelial thickness variables were between 0.7 and 1.9 ?m. The repeatability of MSD was better than 0.4 ?m. The repeatability of PSD was 0.02 or better. Among all epithelial thickness-based variables investigated, PSD provided the best diagnostic power (AUC = 1.00). Using an PSD cutoff value of 0.057 alone gave 100% specificity and 100% sensitivity.ConclusionsHigh-resolution Fourier-domain OCT mapped corneal epithelial thickness with good repeatability in both normal and keratoconic eyes. Keratoconus was characterized by apical epithelial thinning. The resulting deviation from the normal epithelial pattern could be detected with very high accuracy using the PSD variable.Financial disclosure(s)Proprietary or commercial disclosure may be found after the references.

Project description:PURPOSE:To determine optimal objective, machine-derived variables and variable combinations from Scheimpflug and spectral-domain (SD) OCT imaging to distinguish the clinically unaffected eye in patients with asymmetric keratoconus (AKC) from a normal control population. DESIGN:Retrospective case-control study. PARTICIPANTS:Thirty clinically unaffected eyes with no physical findings on slit-lamp examination, no definitive abnormalities on corneal imaging, and corrected distance acuity of 20/20 or better from 30 patients with highly AKC eyes and 60 eyes from 60 normal control patients who had undergone uneventful LASIK with at least 2 years of stable follow-up (controls). METHODS:Scheimpflug and SD OCT imaging were obtained in all eyes, and receiver operating characteristic (ROC) curves were generated to determine area under the curve (AUC), sensitivity, and specificity for each machine-derived variable and variable combination. MAIN OUTCOME MEASURES:Distinguishing AKC eyes from controls as determined by AUC, sensitivity, and specificity. RESULTS:No individual machine-derived metric from Scheimpflug or SD OCT technology yielded an AUC higher than 0.75. Combining 5 Scheimpflug metrics (index height decentration [IHD], index vertical asymmetry [IVA], pachymetry apex, inferior-superior value, and Ambrosio's Relational Thickness Maximum [ARTmax]) yielded the best Scheimpflug results (AUC 0.86, sensitivity 83%, specificity 83%). Combining 11 SD OCT thickness metrics (minimum-median, temporal outer, superior nasal outer, minimum, epithelium minimum-maximum, epithelial standard deviation, superior inner, superior outer, superior temporal outer, superior nasal inner, central) yielded the best SD OCT results (AUC 0.96, sensitivity 89%, specificity 89%). Combining 13 total Scheimpflug/SD OCT metrics yielded the best results overall (AUC 1.0, sensitivity 100%, specificity 100%). The most impactful variables in combined models included epithelial thickness variability and total focal corneal thickness variability from SD OCT and anterior curvature and topometric indices from Scheimpflug technology. No posterior corneal metrics were impactful in modeling. CONCLUSIONS:Individual machine-derived metrics from Scheimpflug and SD OCT imaging poorly distinguished normal eyes from minimally affected eyes from patients with highly AKC. Combined SD OCT metrics performed better than combined Scheimpflug metrics. Combining anterior curvature and asymmetry indices from Scheimpflug with regional total thickness and epithelial thickness variability metrics from SD OCT clearly distinguished the 2 populations. Posterior corneal indices were not useful in distinguishing populations.

Project description:Custom high-resolution high-speed anterior segment spectral domain Optical Coherence Tomography (OCT) was used to characterize three-dimensionally (3-D) corneal topography in keratoconus before and after implantation of intracorneal ring segments (ICRS). Previously described acquisition protocols were followed to minimize the impact of the motions of the eye. The collected set of images was corrected from distortions: fan (scanning) and optical (refraction). Custom algorithms were developed for automatic detection and classification of volumes in the anterior segment of the eye, in particular for the detection and classification of the implanted ICRS. Surfaces were automatically detected for quantitative analysis of the corneal elevation maps (fitted by biconicoids and Zernike polynomials) and pachymetry. Automatic tools were developed for the estimation of the 3-D positioning of the ICRS. The pupil center reference was estimated from the segmented iris volume. The developed algorithms are illustrated in a keratoconic eye (grade III) pre- and 30 days post-operatively after implantation of two triangular-section, 0.3-mm thick Ferrara ring segments. Quantitative corneal topographies reveal that the ICRS produced a flattening of the anterior surface, a steepening of the posterior surface, meridional differences in the changes in curvature and asphericity, and increased symmetry of the anterior topography. Optical distortion correction through the ICRS (of a different refractive index from the cornea) allowed accurate pachymetric estimates, which showed increased thickness in the ectatic area as well as in peripheral corneal areas. Automatic tools allowed estimation of the depth of the implanted ICRS ring, as well as its rotation with respect to the pupil plane. Anterior segment sOCT provided with fan and optical distortion correction and analysis tools is an excellent instrument for evaluating and monitoring keratoconic eyes and for the quantification of the changes produced by ICRS treatment.

Dataset Information

SD-OCT analysis of regional epithelial thickness profiles in keratoconus, postoperative corneal ectasia, and normal eyes.

Publications

SD-OCT analysis of regional epithelial thickness profiles in keratoconus, postoperative corneal ectasia, and normal eyes.

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