A review of keratoconus: diagnosis, pathophysiology and genetics. Mas-Tur V, MacGregor C, Jayaswal R, et al. Cellular incursion into Bowman’s membrane in the peripheral cone of the keratoconic cornea. The D144E substitution in the VSX1 gene: a non-pathogenic variant or a disease causing mutation? Ophthalmic Genet. *Holland DR, Maeda N, Hannush SB, Riveroll LH, Green MT, Klyce SD, Wilson SE. Detection of keratoconus before keratorefractive surgery. Detection of keratoconus before refractive surgery. Videokeratography of the fellow eye in unilateral keratoconus. *Rabinowitz YS, Nesburn AB, McDonnell PJ. Computer-assisted corneal topography in parents of patients with keratoconus. Computer-assisted corneal topography in family members of patients with keratoconus. Molecular genetic analysis in autosomal dominant keratoconus. Rabinowitz YS, Maumenee IH, Lundergan MK. The differential diagnosis includes artefact, contact lens-induced corneal warpage and various types of corneal disease and surgery. These include the asymmetry and regularity indices, inferior-superior value, difference in central power, keratoconus predictability index, enhanced ectasia display and, in certain devices, neural networks. Topographic indices have been developed to detect very early stages of ectasia and quantify progression. Keratoglobus has a more even thinning affecting the whole cornea, which expands more symmetrically, with relatively little effect on the refraction. With further progression, the “bows” of the “tie” may meet in the inferior periphery, producing a pattern resembling a more inferior keratoconus. In pellucid marginal degeneration, the thinning is further inferiorly, creating a “droopy bow tie” area of corneal steepening, associated with high orders of regular astigmatism. Keratoconus can be classified according to the severity, location and shape of the cone. This causes corneal irregularity which can only be improved by glasses in the earliest stages. In keratoconus the cornea has an exaggerated prolate shape with paracentral corneal steepening, which most commonly occurs inferiorly, with corneal flattening in the opposite hemisphere. In both types, in the early stages, the classical clinical signs may be absent, so the diagnosis relies upon topographic findings alone. ![]() Secondary ectasia occurs as a result of thinning due to corneal surgery or inflammatory stromal melt. In primary corneal ectasias, noninflammatory stromal thinning causes the cornea to progressively protrude forwards.
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