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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 ...
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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]
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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.
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.
They are each about 1.5-2.5 μm in thickness. The anterior lamellae interweave more than posterior lamellae. The fibrils of each lamella are parallel with one another, but at different angles to those of adjacent lamellae. The lamellae are produced by keratocytes (corneal connective tissue cells), which occupy about 10% of the substantia propria.
It is composed of strong, randomly oriented collagen fibrils in which the smooth anterior surface faces the epithelial basement membrane and the posterior surface merges with the collagen lamellae of the corneal stroma proper. [1] In adult humans, Bowman's layer is 8-12 μm thick. [2] With ageing, this layer becomes thinner.