True about keratoconus -

Signs of Keratoconus. Following signs may be elicited:1. Window reflex is distoed.2. Placido disc examination shows irregularity ofthe circles (Fig. 5.18B).3. Keratometry depicts extreme malalignment ofmires.4. Photokeratoscopy reveals distoion of circles.5. Slit lamp examination (Fig. 5.18C) may showthinning and ectasia of central cornea, opacity atthe apex and Fleischer's ring at the base of cone,folds in Descemet's and Bowman's membranes.Very fine, veical, deep stromal striae (Vogt lines)which disappear with external pressure on theglobe are peculiar feature.6. On retinoscopy a yawning reflex (scissor reflex)and high oblique or irregular astigmatism isobtained.7. On distant direct ophthalmoscopy an annulardark shadow (due to total internal reflection oflight) is seen which separates the central andperipheral areas of cornea (oil droplet reflex).8. Munson's sign, i.e. localised bulging of lower lidwhen patient looks down is positive in late stages REF:Comprehensive ophthalmology,4th edition,pg no.119