Ans. B: It manifests just after bih Keratoconus is frequently due to a congenital weakness of the cornea, though it manifests itself after pubey. However it can occur secondarily following trauma or Down's syndrome. Keratoconus is divided into mild, moderate, and advanced. Mild keratoconus - External and corneal signs are often absent or minimal. - A history of multiple inadequate spectacle corrections of one or both eyes may be noted and may include oblique astigmatism on refraction as well as moderate-to-high myopia. - Irregularly astigmatic keratometry values (egg-shaped), not necessarily on the steep side of normal (approximately 45 diopters (D)), are consistent with diagnosis. Diagnosis can be confirmed with computer-assisted videokeratography, which may reveal corneal inferior steepening (approximately 80% of keratoconus cases), central corneal astigmatic steepening (approximately 15% of keratoconus cases), or even bilateral temporal steepening (extremely rare). Diagnosis may also be aided by applying a diagnostic rigid contact lens with its base curve equal to the flat keratometry value. One observes a typical nipple pattern by use of sodium fluorescein dye in the underlying tear film. Moderate keratoconus One or more corneal signs of keratoconus are often present. Enhanced appearance of the corneal nerves is noted. Approximately 40% of eyes in patients with moderate keratoconus develop Vogt striae (fine-stress lines) in the deep stroma. Approximately 50% develop the deposition of iron in the basal epithelial cells in a (often paial) ring shape at the base of the conical protrusion called the Fleischer ring. Approximately 20% develop corneal scarring. Superficial corneal scarring can be fibular, nebular, or nodular. Deep stromal scarring may occur, perhaps representing resolved mini-hydrops events. Some patients show scarring at the level of the Descemet membrane (posterior limiting lamina), consistent in appearance with posterior polymorphous corneal dystrophy. Paraxial (usually inferior to the pupil) stromal thinning may be appreciated. Keratometry values typically increase to 45-52 D. Distoion of the retinoscopy and direct ophthalmoscope red pupillary reflex may allow observation of "scissoring" or an inferior distoion termed the oil drop sign. The Munson sign is noted when, upon downgaze, a "V" shape is noted in the cornea's profile against the lower lid margin, an accentuation of the conical shape of the modest to advanced keratoconus cornea. Advanced keratoconus This often results in keratometry values greater than 52 D and enhancement of all corneal signs, symptoms, and visual loss/distoion. Vogt striae are seen in approximately 60% of eyes, and Fleischer ring and/or scarring are seen in approximately 70% of eyes. Acute corneal hydrops can occur. Treatment: In the early stages, vision may be improved with spectacles but contact lens are more beneficial as they eliminate the irregular corneal curvature. If the disease progresses and the cone hydrated, the most satisfactory treatment is corneal transplantation.