Doctors assess the severity of eyelid droop by taking precise measurements of the eyelid and eye opening. You can screen for the problem yourself by looking straight ahead in a mirror. As you look at your eye, a sizable part of your iris (the eye's colored circle) should be visible above your pupil, and no part of the pupil itself should ever be covered by the eyelid.
If you have ptosis, the drooping eyelid narrows your eye's opening, which makes your affected eye appear smaller than normal. You also may lose the crease (fold of skin) that normally lies between your upper eyelid and eyebrow. If ptosis covers your pupil and limits your vision, you may try to compensate unconsciously by raising your eyebrows. This can cause tension headaches and give your eyes an odd, surprised appearance. You also may tilt your chin up and look down your nose as a way of seeing out from under your eyelid's lower margin.
If you have simple, uncomplicated ptosis, you won't have any other symptoms. If your ptosis is caused by a more serious medical problem, however, you may have additional symptoms that are related to the underlying illness. For example, myasthenia gravis may also cause double vision, weakness in the arms or legs, and difficulty speaking, swallowing or breathing. Among infants with congenital ptosis, approximately 30% also have crossed eyes (strabismus) or some other disorder that affects the eye's position or movement. In ptosis caused by Horner's syndrome, the pupil of the affected eye is unusually small.