Can horses get cataracts?

Yup. In fact, all mammals can get cataracts. Uveitis can cause cataracts, as can age. Juvenile cataracts are congenital and fairly rare in the horse.

Cataract removal is trickier in horses than in other animals, especially in adults. Also, there's no way to replace the lens functionality in such a big animal, at least not yet. The chance of any vision is only 50/50 in adult horses.

Because of this, cataracts in adult and older horses are not often removed surgically. Cataract removal can also cause all kinds of complications...including moon blindness. It's often better to just let the animal go blind in that eye. Foals who have had lenses removed often grow up to be serviceable (but should not be bred as this is usually a genetic condition). They may need special training because of compromised vision.