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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 ...
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]
At its centre, a human corneal stroma is composed of about 200 flattened lamellae (layers of collagen fibrils), superimposed one on another. [1] They are each about 1.5-2.5 μm in thickness. The anterior lamellae interweave more than posterior lamellae.
Diagram of light and four Purkinje images [1] An eye with Purkinje images. Purkinje images are reflections of objects from the structure of the eye. They are also known as Purkinje reflexes and as Purkinje–Sanson images. At least four Purkinje images are usually visible in the normal eye.
The Javal-Schiotz keratometer is a two position instrument which uses a fixed image and doubling size and adjustable object size to determine the radius of curvature of the reflective surface.
Long-term contact lens use can lead to alterations in corneal thickness, stromal thickness, curvature, corneal sensitivity, cell density, and epithelial oxygen uptake. . Other structural changes may include the formation of epithelial vacuoles and microcysts (containing cellular debris), corneal neovascularization, as well as the emergence of polymegethism in the corneal endoth
The appearance of visual complaints such as halos, glare and monocular diplopia after corneal refractive surgery has long been correlated with the induction of optical aberrations. Several mechanisms may explain the increase in the amount of higher-order aberrations with conventional excimer laser refractive procedures: a change in corneal ...