Astigmatic Vector Analysis of Posterior Cornea - a Comparison Among Healthy, Forme Fruste and Overt Keratoconus Corneas

Study Overview
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Brief Summary
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The main purpose of this study is to determine new diagnostic criteria for an eye disease called keratoconus.

Detailed Description
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Eyes of patients who distinctly present signs of keratoconus, for both eyes, at corneal tomography (an exam commonly used in such cases), and those who present such signs in only one eye were compared to eyes of unaffected patients. Several characteristics of anterior and posterior corneal astigmatism (special emphasis was given to the latter) were collectively assessed among all patients by a method referred to as vectorial analysis. Statistical tests were then performed, in an attempt to highlight differences among those three groups of patients and, eventually, define new diagnostic criteria.

Official Title
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Astigmatic Vector Analysis of Posterior Corneal Surface - a Comparison Among Healthy, Forme Fruste and Overt Keratoconus Corneas

Conditions
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Keratoconus

Intervention / Treatment
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* Other: Analysis of anterior and posterior corneal surfaces


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Good-quality Scheimpflug scans (approved by the device in the ''Examination Quality Specification''). Exclusion Criteria: Previous eye surgery or trauma, and any sort of corneal scarring that might interfere with keratometric data acquisition.
Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Healthy corneas (C)<br>Corneas of normal candidates to refractive surgery who did not develop any sign of corneal ectasia after laser in situ keratomileusis during a two year follow-up period were analyzed by an Scheimpflug-based tomographer. Vector astigmatism analysis of anterior and posterior corneal surfaces were studied in accordance to method proposed by Thibos. | Other: Analysis of anterior and posterior corneal surfaces<br>* Corneal data obtained from a Scheimpflug-based topographer were converted to astigmatic vectors in accordance to the method proposed by Thibos<br>* Other names: Thibos' vectorial astigmatism analysis;|
| Overt keratoconus (Kc)<br>Whether both eyes manifested classic Kc-suggestive topographic features, such as corneal steepness higher than 47.20 diopters (D), superior-inferior asymmetry higher than 1.40 D and thinnest pachymetric reading lower than 500 micrometers. Such eyes were analyzed by an Scheimpflug-based tomographer. Vector astigmatism analysis of anterior and posterior corneal surfaces were studied in accordance to method proposed by Thibos. | Other: Analysis of anterior and posterior corneal surfaces<br>* Corneal data obtained from a Scheimpflug-based topographer were converted to astigmatic vectors in accordance to the method proposed by Thibos<br>* Other names: Thibos' vectorial astigmatism analysis;|
| Forme fruste keratoconus (FFKc)<br>Whether only one eye manifested classic Kc-suggestive topographic features, such as corneal steepness higher than 47.20 diopters (D), superior-inferior asymmetry higher than 1.40 D and thinnest pachymetric reading lower than 500 micrometers, and the fellow eye seemed unaffected. Such unaffected eyes were analyzed by an Scheimpflug-based tomographer. Vector astigmatism analysis of anterior and posterior corneal surfaces were studied in accordance to method proposed by Thibos. | Other: Analysis of anterior and posterior corneal surfaces<br>* Corneal data obtained from a Scheimpflug-based topographer were converted to astigmatic vectors in accordance to the method proposed by Thibos<br>* Other names: Thibos' vectorial astigmatism analysis;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Astigmatism corneal vectors (based on keratometric readings at the three millimeter optical zones for both corneal surfaces). | Corneal tomography at an Scheimpflug-based tomographer | Through study completion, an average of 6 months. | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Keratoconus, Corneal Topography, Diagnosis, Keratomileusis, Laser In Situ