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Ptosis and eyelid malpositions
Ptosis is classified by mechanism — aponeurotic, myogenic, neurogenic or mechanical — and two measurements decide: the margin reflex distance (MRD1) and levator function; in any new ptosis the pupils and eye movements are examined first so as not to miss a third nerve palsy or Horner syndrome.
Why it matters in the exam
The commonest form in older adults is aponeurotic — stretching or disinsertion of the levator aponeurosis: a raised lid crease, good levator function, and sometimes after cataract surgery or contact lens wear. Congenital ptosis is myogenic: weak levator function, the lid does not descend well on downgaze (lid lag), and when the lid covers the pupil — a risk of amblyopia that requires early surgery. A normal MRD1 is roughly 4–5 mm, and normal levator function is 12 mm or more.
Neurogenic ptosis: third nerve palsy — complete ptosis with the eye "down and out" and a dilated pupil (a posterior communicating artery aneurysm until proven otherwise); Horner syndrome — mild ptosis of 1–2 mm with a small pupil and slight elevation of the lower lid. Myasthenia gravis — variable ptosis that worsens with fatigue and at the end of the day, with double vision, a twitch of the lid after downgaze (Cogan lid twitch) and improvement after cooling with ice. CPEO — bilateral ptosis with symmetrical limitation of movement and no double vision. Surgery: shortening or reattachment of the levator when function is good, and a frontalis sling when function is weak.
Other malpositions: ectropion — a lower lid turned outwards, mainly from laxity with age, from scarring or from facial nerve palsy, with watering and exposure; entropion — a lid turned inwards with lashes rubbing the cornea, in the lower lid from laxity, and in the upper lid from scarring (trachoma, ocular pemphigoid, Stevens-Johnson syndrome). In Bell palsy the main danger is corneal exposure: lubrication, taping the lid at night and sometimes a gold weight. Floppy eyelid syndrome — lax lids that evert during sleep — is linked to sleep apnoea.
Key points
- Classification: aponeurotic, myogenic, neurogenic, mechanical.
- Normal MRD1 4–5 mm; levator function 12 mm or more.
- Dilated pupil → third nerve; small pupil → Horner syndrome.
- Variable fatigable ptosis → myasthenia gravis.
- Ectropion and entropion: laxity, scarring or palsy.
Summary table
| Type | Finding | Identifying sign | Treatment |
|---|---|---|---|
| Aponeurotic | High crease, good levator function | Older age, contact lenses | Levator advancement |
| Congenital myogenic | Weak levator function, lid lag | Covers pupil → amblyopia | Frontalis sling; early if it covers the pupil |
| Third nerve | Complete ptosis, eye down and out | Dilated pupil | Urgent vascular imaging |
| Horner syndrome | Ptosis of 1–2 mm | Small pupil | Work-up of the sympathetic pathway |
| Myasthenia gravis | Variable, fatigable ptosis | Cogan lid twitch, ice test | Antibody work-up, neurological treatment |
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Sources
- AAO Basic and Clinical Science Course, Section 7: Oculofacial Plastic and Orbital Surgery, 2024-2025 — Classification and management of eyelid disorders
- Royal College of Ophthalmologists: Ophthalmic services guidance — oculoplastic services, 2021 — Ptosis and eyelid malposition
- Kanski's Clinical Ophthalmology, 9th edition (2020) — Eyelids
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.