it's a much smaller world than applying for residency. although there is a formal match for fellowships, many fellowships are secured based upon phone calls from chairman, etc. if you know that you want to do cornea which is a GREAT field, i would get to know the cornea faculty well at your program, get on a cornea research project at some point and work really hard during your residency. while not as competitive as say retina or plastics, it is probably harder to get than neuro-op. bottom line, if you want to do cornea, you probably can. also, cornea has everything to do with optics, so learn your optics well!