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Corneal topography, also known as photokeratoscopy or videokeratography, is a non-invasive medical imaging technique for mapping the anterior curvature of the cornea, the outer structure of the eye. Since the cornea is normally responsible for some 70% of the eye's refractive power , [ 1 ] its topography is of critical importance in determining ...
It is also the principle used in corneal pachymetry, the mapping of corneal topography, ... Available for download (PDF). Scheimpflug, Theodor. 1904. Improved Method ...
However, it may not be as specific as corneal pachymetry, because corneal topography only evaluates the degree and distribution of surface irregularities on the cornea, not the thickness of the cornea. [5] Corneal topography may show a "crab claw-like" appearance, a finding that is seen in both keratoconus and in pellucid marginal degeneration.
Diagnosis is most often by topography. Topography measures the curvature of the cornea and creates a colored "map" of the cornea. Keratoconus causes very distinctive changes in the appearance of these maps that allow doctors to make the diagnosis. Initially, the condition can typically be corrected with glasses or soft contact lenses. [3]
Before corneal refractive surgery such as LASIK, SMILE, and PRK, people must be examined for possible risk factors such as keratoconus. [3]Abnormal corneal topography compromises of keratoconus, pellucid marginal degeneration, or forme fruste keratoconus with an I-S value of 1.4 or more [4] is the most significant risk factor.
Contoura Vision has resulted in vision outcomes better than 6/6 (or 20/20, the standardized normal vision) in multiple patients who were a part of validation trials by the US FDA.
The central corneal power is the second important factor in the calculation formula. To simplify the calculation, the cornea is assumed to be a thin spherical lens with a fixed anterior to posterior corneal curvature ratio and an index of refraction of 1.3375. Central corneal power can be measured by keratometry or corneal topography.
In advanced cases the pterygium can affect vision [10] as it invades the cornea with the potential of obscuring the optical center of the cornea and inducing astigmatism and corneal scarring. [11] Many patients do complain of the cosmetic appearance of the eye either with some of the symptoms above or as their major complaint.