Sudden Droopy Eyelid in Dogs (Ptosis): Causes and Veterinary Urgency

Acute unilateral or bilateral ptosis in dogs is a neurologic or ophthalmic emergency requiring prompt veterinary evaluation.

Differential Diagnosis (VETS PION)

• Vascular: Horner's syndrome (sympathetic loss → ptosis, miosis, enophthalmos, third eyelid protrusion). Causes: trauma, neoplasia, otitis media, idiopathic.
• Eyelid: Trauma, laceration, neoplasm (meibomian gland adenoma), blepharospasm.
• Traumatic: Orbital fracture, retrobulbar hemorrhage.
• Systemic: Myasthenia gravis (fatigable weakness, megaesophagus), hypothyroidism, botulism, tick paralysis.
• Paralysis: Facial nerve (CN VII) — also lip/ear droop, decreased blink. Bell's palsy equivalent.
• Inflammatory: Orbital cellulitis, abscess, immune-mediated (MUE).
• Ocular: Corneal ulcer (pain → blepharospasm mimics ptosis), uveitis, glaucoma.
• Neoplastic: Orbital tumor, nerve sheath tumor, metastatic.

Diagnostic Workup

1. Neurologic exam: cranial nerves, proprioception, reflexes.
2. Ophthalmic: Schirmer tear test, fluorescein stain, tonometry, fundoscopy.
3. Phenylephrine test: confirms Horner's (dilates pupil if postganglionic).
4. Bloodwork: CBC, chem, T4, AChR antibody (myasthenia), tick panel.
5. Imaging: Skull/orbital X-ray, CT, MRI (brainstem, spinal cord).

Treatment

Target underlying cause. Supportive: lubricants if corneal exposure. Prognosis varies: Horner's often idiopathic/resolves; myasthenia requires lifelong management; neoplasia guarded.

Do not wait—sudden ptosis can signal life-threatening conditions (botulism, brainstem lesion).