Have your dog's eyes checked regularly. If your older dog's eye shows any irregularities it is very important to contact your vet. A dog's eye is a very delicate, irreplaceable organ and while cataracts may not be treatable, an eye disease could be.
If you have any doubt, go to the vet, as mild conditions can cause a senior dog's eyesight to deteriorate quite quickly. Do not put anything in or near the eye that is not specifically labeled for canine ophthalmic use (particularly antiseptics), and don't use an old eye medication prescribed by your vet for a previous situation. It is important that any growths or swellings near your dog's eyes be treated by your veterinarian immediately to avoid potential complications.