Early Detection Of Keratoconus Research Articles

Subclinical keratoconus detection by pattern analysis of corneal and epithelial thickness maps with optical coherence tomography

To screen for subclinical keratoconus by analyzing corneal, epithelial, and stromal thickness map patterns with Fourier-domain optical coherence tomography (OCT). Four centers in the United States. Cross-sectional observational study. Eyes of normal subjects, subclinical keratoconus eyes, and the topographically normal eye of a unilateral keratoconus patient were studied. Corneas were scanned using a 26,000 Hz Fourier-domain OCT system (RTVue). Normal subjects were divided into training and evaluation groups. Corneal, epithelial, and stromal thickness maps and derived diagnostic indices, including pattern standard deviation (PSD) variables and pachymetric map-based keratoconus risk scores, were calculated from the OCT data. Area under the receiver operating characteristic curve (AUC) analysis was used to evaluate the diagnostic accuracy of the indices. The study comprised 150 eyes of 83 normal subjects, 50 subclinical keratoconus eyes of 32 patients, and 1 topographically normal eye of a unilateral keratoconus patient. Subclinical keratoconus was characterized by inferotemporal thinning of the cornea, epithelium, and stroma. The PSD values for corneal (P < .001), epithelial (P < .001), and stromal (P = .049) thickness maps were all significantly higher in subclinical keratoconic eyes than in the normal group. The diagnostic accuracy was significantly higher for PSD variables (pachymetric PSD, AUC = 0.941; epithelial PSD, AUC = 0.985; stromal PSD, AUC = 0.924) than for the pachymetric map-based keratoconus risk score (AUC = 0.735). High-resolution Fourier-domain OCT could map corneal, epithelial, and stromal thicknesses. Corneal and sublayer thickness changes in subclinical keratoconus could be detected with high accuracy using PSD variables. These new diagnostic variables might be useful in the detection of early keratoconus. Oregon Health and Science University (OHSU) and Drs. Li, Tan, and Huang have a significant financial interest in Optovue, Inc. These potential conflicts have been reviewed and managed by OHSU. Dr. Brass receives research grants from Optovue, Inc. Drs. Chamberlain and Weiss have no financial or proprietary interest in any material or method mentioned.

Aberraciones corneales anteriores y posteriores medidas mediante imágenes de Scheimpflug en el queratocono en niños

ObjectiveIdentify utility of anterior and posterior aberrations in children to differentiate healthy and keratoconus corneas by Scheimpflug imaging with the Oculus Pentacam®. MethodA retrospective comparative observational study of children between 5 and 15 years was conducted. A group with healthy corneas and another group with keratoconus stage 1 and 2. All patients were examined including Scheimpflug's images. Were studied the following variables: spherical refractive defect, cylindrical defect, BCVA, keratometry maximum, Minimum and medium, topographic astigmatism and anterior and posterior aberrations. Student t-test and unpaired Mann-Whitney test was used. ResultsAlmost all aberrations of the anterior surface except the primary and secondary horizontal coma were founded that significant differences between the groups exists. Primary vertical coma, primary spherical aberration, coma and coma-like RMS: posterior corneal surface significant differences between groups were found. In children with healthy corneas was found that in back surface vertical coma, spherical aberration, coma and coma-like RMS frequently. In the keratoconus between the anterior and posterior corneal surface exits significant differences in vertical coma, coma-RMS and coma-like RMS. ConclusionsThe measurements of the aberrations of the anterior surface Sheimpflug imaging measures are useful in early detection of keratoconus in children. The posterior corneal surface aberrations are not useful since they are not in accordance with the optical properties of the cornea.

Ocular Biomechanics: Measurement Parameters and Terminology

doi:10.3928/1081597X-20110519-01 T raditionally, biomechanical properties of the cornea have been assessed in vitro by measuring stress-strain and Young modulus on corneal strips. In 2005, the Ocular Response Analyzer (ORA; Reichert Technologies, Depew, New York) was launched as the fi rst commercial device claiming to provide in vivo measurements of corneal biomechanics.1 It utilizes a dynamic bi-directional applanation process in which two applanation pressure measurements are recorded: one while the cornea is moving inward, and the other as the cornea returns. The primary output measurements are Goldmann-correlated intraocular pressure (IOPg), and a new parameter called corneal hysteresis (CH), defi ned by Reichert as the difference between the two pressure values of the inward and outward applanations. The ORA provides two additional new parameters: corneal-compensated intraocular pressure (IOPcc) and corneal resistance factor (CRF), which was thought to be an indicator of the overall “resistance” of the cornea. Given the promising nature of the possibility of measuring biomechanics in vivo, many studies covering a wide range of topics have been performed and published using the ORA in the past 5 years. The majority of articles addressed the following topics: 1) IOP, CH, and CRF measurements in patients with glaucoma, 2) changes in CH and CRF after corneal refractive surgery, and 3) changes in CH and CRF in keratoconic patients and the possibility of using CH and CRF for assisting in the detection of early keratoconus. With this initial body of articles published, we can now start to evaluate the clinical utility of the ORA in refractive surgery. This editorial reviews the use of the ORA for measuring IOP, CH, CRF, and future parameters and discusses the commonly used terminology. IOP MEASUREMENTS Corneal-compensated IOP has been shown to be comparable to IOP measured with dynamic contour tonometry,2 and IOPcc has also been shown to be independent of central corneal thickness.3 Therefore, as the proportion of patients electing to have corneal refractive surgical procedures continues to increase, IOPcc will remain a valid and powerful tool to diagnose and monitor patients with glaucoma after corneal surgery.

Clinical applications of Scheimpflug imaging

Since the Scheimpflug principle was first described more than a century ago, there has been great interest among ophthalmologists in the use of Scheimpflug cameras in anterior-segment imaging. Scheimpflug cameras have advanced significantly and modern-day instruments provide comprehensive imaging and topographic data of the anterior segment. The clinical applications and limitations of Scheimpflug imaging in corneal, cataract and refractive surgery patients are discussed. This article also covers an assessment of anterior chamber biometry for precataract surgery calculations and glaucoma screening, corneal topography of the anterior and posterior corneal surfaces using elevation data for early detection of keratoconus and post-laser in situ keratomileusis ectasia, lens changes with accommodation, lens transparency for cataract grading, and integrity and density of the posterior capsule for posterior-capsule opacification grading using the currently commercially available Scheimpflug cameras.

Corneal topography.

The heightened interest in refractive corneal surgery has resulted in the increased utility of videokeratography in clinical practice. During this past year, studies have provided new information about the accuracy, reproducibility, limitations, and comparative strengths and weaknesses of different topographic devices. Videokeratography studies have yielded new information about the effects of surgical procedures such as excimer laser photorefractive keratectomy, radial keratotomy, penetrating keratoplasty, trabeculectomy, and strabismus surgery on the shape of the cornea. The use of these devices in fitting patients with keratoconus and patients who have had radial keratotomy with contact lenses is illustrated and subtle topographic abnormalities induced by rigid and soft contact lenses are reported. The early detection of keratoconus with videokeratography has provided new insights into the genetics of this disorder. Computer-assisted topographic devices are rapidly gaining acceptance as screening tools for the detection of early keratoconus in candidates for myopic refractive surgery.

Videokeratography of the Fellow Eye in Unilateral Keratoconus

To identify a population of keratoconus patients with unilateral disease based on clinical findings and slit-lamp biomicroscopy and examination with a nine-ring photokeratoscope (Corneascope) and to study the topography of the clinically normal fellow eye with videokeratography. Clinical charts and Polaroid Corneascope photographs of both eyes of 200 patients with a diagnosis of keratoconus from three large cornea referral practices in the Los Angeles area were retrospectively reviewed. Patients whose clinical findings were within normal limits and whose Corneascope Polaroid photographs had concentric rings with no detectable abnormalities, consistent with a diagnosis of keratoconus in one eye, were considered unilateral. These patients were recalled to our clinic, and the topography of the apparently normal eye was studied using a Corneascope and a computer-assisted videokeratoscope, the Topographic Modeling System, on the same day. Based on examination with a slit-lamp biomicroscope and the Corneascope, eight patients had unilateral disease. Videokeratography in seven of the eight fellow eyes displayed a pattern of inferior steepening suggesting "early keratoconus." All seven eyes had a positive "I - S value," a quantitative measure, indicating increased dioptric power below the corneal apex. Our findings suggest that keratoconus is almost always bilateral. These data support genetic influences in the pathogenesis of this disorder. Additionally, videokeratography data presented might prove useful in the detection of early keratoconus and refining patient selection for myopic keratorefractive procedures.