Tonometer used for irregular surface of the cornea:

Ans. a. Mackey Marg tonometer Mackey Marg Tonometer Concept is force required to keep the flat plate of a plunger flush with a surrounding sleeve against the pressure of corneal deformation. It is accurate in eyes with scarred, edematous and irregular cornea Perkin's Tonometer Perkin's Tonometer uses prism as Goldmann but is counterbalanced, so that tonometry is performed in any position. Prism illuminated by battery powered bulbs. Force is adjusted manually. It is poable Dreger's Tonometer Similar to Perkin's but uses different set of prisms and operated with a motor adjusting the force on these prisms Maklakov Tonometer It is constant force tonometer lop is estimated by measuring the area of cornea flattened by a known weight. It consist of dumbbell-shaped metal cylinder with flat end-plates of polished glass on either ends of diameter 10 mm. Tonometers weighing 5, 7.5, 10 and 15 gms are used to measure IOP.