Which type of refractive error is seen in keratoconus-

Ans. is 'a' i.e., Irregular astigmatism. Examination findings o The hallmark of keratoconus is central or paracentral stromal thinning, apical protrusion of the anterior cornea and irregular astigmatism. The cornea thins near the center and progressively bulges forwards, with the apex of cone always being slightly below the center of the cornea. o Corneal topography is the most sensitive method for detecting keratoconus, it can document the presence of keratoconus even before keratometric or slit lamp findings become apparent o On examination following findings are there:- i) Distorted window reflex (corneal reflex). ii) Placido disc examination shows irregularity of the circles. iii) Keratometry shows irregular astigmatism where the principle meridian are no longer 90deg apart and the mires cannot be superimposed, i.e., malaligned mires. iv) Slit lamp examination shows : - a) Thinning and ectasia of central cornea b) Opacity at the apex c) Fleisher's ring at the base of the cone. d) Folds in Descemet's and Bowman's membrane e) Very fine, vertical, deep stromal stria (Vogt lines) which disappear with external pressure on the globe. v) On retinoscopy: - A Yawning reflex (Scissor reflex) and high oblique or irregular astigmatism is obtained. vi) On distant direct ophthalmoscopy: - Oil droplet reflex, i.e., an annular dark shadow which separates the central and peripheral areas of the cornea. vii) Munson's signs: - Localized bulging of the lower lid when the patient looks down. It is a late sign. viii) Prominent corneal nerves.