There are lots of reasons why a rabbit might have runny eyes:
Tooth disease is a very common cause of weepy eyes in rabbits. This is because rabbits have long teeth with roots very close to their eyes. If one of their teeth grows too long, becomes inflamed or develops an infection the eye are likely to be affected.
Blocked tear ducts
The tear ducts (the tubes that drain their tears) are likely to block if something gets stuck inside them (such as a grass seed) or if your rabbit has been born with particularly narrow ducts. When tear ducts become blocked, tears can’t drain away. Rabbits with short faces such as the ‘lop’ and dwarf breeds are especially troubled by this problem.
Infected eyes (bacterial conjunctivitis) often look sticky and develop a creamy, yellow or green discharge.
Nose, throat and lung infections can also affect the eyes. If tear ducts also become inflamed or infected they stop being able to drain tears from the eye. Rabbit ‘snuffles’ caused by the Pasteurella germ is a common infection.
Injuries to the eye cause lots of tears to be produced – this is the body’s natural response to try to protect and heal the eye.
Extra eye lashes
Occasionally, tiny eye lashes grow from the inside of a rabbit’s eyelid. These little hairs constantly rub against the eye and irritate it (causing weeping). Unless these hairs are removed, they will continuously irritate. They can even cause eye ulcers which can be very serious.