Hello Mate...

This solely depends on the extent of weakness of eyesight due to Keratoconus problem. They do have tests of eyesight but they are not very strict. However, if the situation is serious such that you're not able to distinguish colours and there are certain limits to myopia(-2.5 D) and hyper metropia not more than 3.5 D which if you fail, you will be denied entry to NDA. Also, eyesight requirements differ for Army, Navy and Airforce.