If the cornea becomes scarred, swollen or cloudy — after an injury, a serious infection, keratoconus, or an inherited condition — light cannot pass through cleanly. Vision drops, and no strength of glasses can bring it back, because the problem is the window itself, not the focus.
A corneal transplant (medically, keratoplasty) replaces the damaged cornea with healthy donor tissue.
Here is what has changed, and what most people don't know: corneal transplantation is no longer all-or-nothing. In many cases only the diseased layer is replaced while your own healthy layers stay in place. That means fewer stitches, faster visual recovery and a substantially lower chance of rejection than the older full-thickness technique. Which type you need depends entirely on which layer of your cornea is affected.