View clinical trials related to Disorders, Refractive.
Filter by:Corneal topography allows the measure of the radii of curvature and of the thickness of the cornea. It is essential for diagnosis in ophthalmology and allows to highlight corneal irregularities such as a keratoconus, or too thin corneas which are a contra-indication for laser refractive surgery. Several types of corneal topographers are commercially available. Some as the Orbscan(r), operate by analyzing the image of the patterns of a Placido disk associated with a light slit, allowing the collection of thousands of points of the anterior and posterior surface of the cornea. More recent systems such as the Pentacam(r) are based on automatic rotary cameras which capture images of the whole anterior segment of the eye. The aim of this study is to compare two topographs, the Pentacam(r) and the Orbscan(r) and, more specifically, the central corneal pachymetry measurements measured pre- and postoperatively.
In refractive surgery, stromal ablation depth is fundamental because it determines the thickness of the residual posterior wall. The posterior wall is an essential element that guarantees the refractive stability and the long term prevention of corneal ectasia after corneal refractive surgery. A minimum thickness of more or less 300 microns is universally accepted. Its calculation is based on well-known formulas, such as Munnerlynn ones. With the excimer laser platform last generation WaveLight® Allegretto® EX-500 of Alcon, a new treatment option called "wavefront optimized" is offered for myopia, astigmatism and hyperopia. The ablation profile has been developed to save stromal tissue consumption and to favor the quality of vision, by optimizing connections between the optical zone and the transition zone of the photoablation. Alongside the theoretical formulas, evaluation of the depth of ablation may be defined by differential ultrasonic pachymetry or by topographical analysis pre and postoperatively. The latter is currently the method of reference to assess the corneal thickness.