Treatment of ptosis is not always cosmetic and often medically necessary to relieve visual obstruction. The method of treatment for the droopy eyelid, however, would depend on the specific cause and the severity of the ptosis.
In the event that the condition is the consequence of the normal ageing process, or if it was a congenital case, your eye specialist may state that the condition is not damaging to your health. In such cases, there may be no need, except for aesthetic reasons to correct the droopy eyelid(s). Plastic surgery is then an option here to reduce the drooping eyelid(s).
In the event that your eye specialist finds that your ptosis is brought about by an underlying medical condition, the priority here would then be to first treat the condition that first brought about ptosis in the first place. With the condition under control, the drooping will typically cease at that point.
Should your case of ptosis cause an obstruction to normal vision, surgery may then be required to correct the drooping eyelid, and to restore your visual ability.