How can a doctor identify cornea shape change?

Corneal change. An eye doctor can see cornea shape changes by measuring the cornea using a keratometer or topographer. These instruments measure the cornea shape and quantify the steepness values. If changes are severe, it may be detectable at the slit lamp during your eye exam as well.
Special imaging. Images of the cornea known as topographic maps of the cornea are used to detect subtle shape change. This is commonly used in lasik.