Does subconjunctival hemorrhage usually cause many symptoms?

Usually none: This is a benign bleeding from a small vein in the space under the clear conjunctiva over the white of the eye. Due to oxygen exposure it stays very red until absorbed. It can spread over a broad area and look very dramatic. Usually there are no symptoms except the redness. If the vision is changed, or there is pain, see your ophthalmologist. Otherwise you can wait it out.

No: Usually it does not, unless it is from excess rubbing from ocular irritation. Consider an evaluation with your eye doctor if it is recurrent because you may have a bleeding disorder or something serious.