The colored part of the eye is called the iris, and it is covered in front by a clear “windshield,” which is the cornea. Sometimes, if the iris is damaged or irregular, extra light passes into the eye that can be bothersome for patients. It is indeed one of the functions of the iris to regulate light entry into the eye.
If the iris isn’t the right shape, it can sometimes be made better with stitches. But if you think about passing needles behind the “windshield” of the cornea, you can quickly imagine that it is not easy to tie knots once you pass the thread, because the windshield is in your way! There are special techniques to place these kinds of stitches, but it is not a very easy process.