In ophthalmology, ptosis is an abnormally low position (drooping) of the upper eyelid which may grow more or less severe during the day.
Ptosis occurs when the muscle that usually raises the eyelid (levator palpebrae superioris) is not strong enough to do so. It can affect one eye or both eyes and is more common in the elderly, as muscles in the eyelids may begin to deteriorate. One can, however, be born with ptosis, as it is hereditary. Ptosis may be caused by damage/trauma to the muscle which raises the eyelid, or damage to the nerve which controls this muscle. Such damage could be a sign or symptom of an underlying disease such as diabetes mellitus, a brain tumor, and diseases which may cause weakness in muscles or nerve damage, such as myasthenia gravis.
Depending upon the cause it can be classified into:
- Neurogenic ptosis which includes IIIrd cranial nerve palsy, Horner’s Syndrome, Marcus Gunn jaw winking syndrome, IIIrd cranial nerve misdirection.
- Myogenic ptosis which includes myasthenia gravis, myotonic dystrophy, ocular myopathy, simple congenital ptosis, blepharophimosis syndrome
- Aponeurotic ptosis which may be involutional or post-operative.
- Mechanical ptosis which occurs due to edema or tumors of the upper lid
- Neurotoxic ptosis which is a classic symptom of envenomation by elapids such as cobras or kraits etc. Neurotoxic ptosis is a precursor to respiratory failure and eventual suffocation caused by complete paralysis of the thoracic diaphragm. Urgent medical intervention is therefore required.