The curvature of the cornea can be measured by

The 'keratometry' or 'ophthalmometry' is an objective method of estimating corneal astigmatism by measuring the curvature of the central cornea. The keratometry readings are not of much value in routine refraction for prescribing glasses but are of utmost value for prescribing contact lenses and for calculating the power of the intraocular lens to be implanted. Principle. Keratometer is based on the fact that the anterior surface of the cornea acts as a convex mirror; so the size of the image produced varies with its curvature. Therefore, from the size of the image formed by the anterior surface of the cornea (first Purkinje image), the radius of curvature of the cornea can be calculated. The accurate measurement of the image size is obtained by using the principle of visible doubling. Reference : A K KHURANA Comprehensive Ophthalmology edition 4,page-554