Oculoplastics · Patient & Surgeon Series
A droopy eyelid
is usually a tendon.
Occasionally it is a warning.
Ptosis — an upper eyelid sitting lower than it should — is most often a slowly stretched levator tendon after decades of blinking. Sometimes it is a nerve, a muscle disease, or an aneurysm pressing on the third cranial nerve. Here is how the droop is measured, which signs make it urgent, and how each repair actually works.
MRD1
approaches
ptosis eye drop
Section 01 — What Ptosis Is
The lid is held up
by two muscles
and one long tendon.
The upper eyelid does not hang passively. It is lifted by the levator palpebrae superioris, a muscle that runs forward from the back of the orbit and becomes a broad, thin tendon — the levator aponeurosis — that fans out and attaches to the tarsal plate, the firm strip of tissue inside the lid. A second, smaller muscle underneath it, Müller's muscle, adds a couple of millimetres of lift and is driven by the sympathetic nervous system.
Blepharoptosis (usually shortened to ptosis) is what happens when any link in that chain weakens: the nerve that drives the levator, the muscle itself, the tendon's attachment to the tarsus, or the sympathetic supply to Müller's muscle. It can also be imitated by things that are not ptosis at all, such as excess upper-lid skin draping over the lashes. Working out which link has failed is the whole diagnosis — and it decides both how urgent the problem is and which repair will work.
Ptosis is a drooping upper eyelid caused by weakness somewhere in the system that lifts it. In adults the commonest cause by far is aponeurotic ptosis: the levator tendon gradually stretches or loosens from its attachment with age, contact lens wear or previous eye surgery, while the muscle itself stays healthy. Children are more often born with a poorly developed levator muscle. Less common but important causes include third nerve palsy, Horner syndrome and myasthenia gravis, which need medical assessment before any surgery. Treatment depends on how much the lid droops (MRD1) and how well the levator still works (levator function): tightening the tendon, shortening Müller's muscle, or slinging the lid to the brow.
Section 02 — Interactive
One measurement
describes the droop: MRD1.
Margin-reflex distance 1 (MRD1) is the gap, in millimetres, between the upper lid margin and the bright light reflex on the centre of the cornea when the patient looks at a penlight. It is the standard way to put a number on ptosis. Lower the lid below and watch what happens to the pupil — and to the upper part of the visual field.
In most adults the upper lid rests around 4 to 5 mm above the light reflex. Clinicians commonly describe ptosis by how far the lid has fallen from that baseline — roughly 2 mm for mild, 3 mm for moderate, and 4 mm or more for severe — though exact cut-offs vary between textbooks. Once MRD1 falls to about 2 mm or less, the lid usually starts to clip the upper pupil, and patients notice it first in the top of their vision: reading a high shelf, driving under a sun visor, or the habit of tilting the chin up and raising the eyebrows to see.
Section 03 — Red Flags
When a droopy lid
is an emergency,
not a cosmetic issue.
Most ptosis develops over years and is harmless apart from the vision and appearance it affects. A small group of presentations are neurological signs, and the ptosis is simply the visible part of something more serious. These are the patterns that need same-day medical assessment rather than an elective oculoplastic referral.
| Pattern | What it may mean | Why it matters |
|---|---|---|
| Sudden ptosis + double vision + a large pupil | Third (oculomotor) nerve palsy with pupil involvement | Can be caused by a posterior communicating artery aneurysm compressing the nerve — a neurosurgical emergency requiring urgent vascular imaging |
| Mild ptosis + small pupil on the same side | Horner syndrome (interrupted sympathetic supply to Müller's muscle and the iris dilator) | New Horner syndrome with neck or face pain can indicate carotid artery dissection; it can also signal a lung-apex tumour |
| Ptosis that worsens through the day, with variable double vision | Ocular myasthenia gravis | An autoimmune neuromuscular disorder that can generalise to swallowing and breathing muscles; treated medically, and lid surgery done blind to it can disappoint |
| Slowly progressive ptosis in both eyes with limited eye movements | Chronic progressive external ophthalmoplegia (CPEO) or a muscular dystrophy | A systemic myopathy — affects surgical planning because weak eye closure raises the risk of corneal exposure |
| Ptosis with a lid lump, swelling or a change in lid shape | Mechanical ptosis from a mass, chalazion or orbital lesion | The cause needs to be identified and treated; lifting the lid alone misses it |
Section 04 — The Second Number
Levator function
decides which operation.
If MRD1 says how far the lid has fallen, levator function says how much power is left to lift it. With the brow pressed firmly so the forehead cannot help, the examiner measures how far the lid margin travels from full downgaze to full upgaze. Normal excursion is around 15 mm.
The figure sorts patients into broad groups, with slightly different cut-offs between authors: good function (roughly 10 mm or more), fair function (around 5 to 10 mm) and poor function (around 4 mm or less). Good function means the muscle works and the problem lies in the tendon or Müller's muscle, so a tightening procedure will transmit that power to the lid. Poor function means there is little muscle to work with, and the lid has to borrow lift from somewhere else — usually the brow.
Two further checks round out the work-up: the tear film and blink (a lid lifted over a dry or poorly protected cornea can cause exposure problems), and the other eye. Under Hering's law both upper lids receive equal nerve drive, so lifting a single droopy lid sometimes unmasks a milder droop on the opposite side that the brain had been compensating for.
Section 05 — Treatment
Three operations
and one eye drop,
matched to the anatomy.
Ptosis repair is about choosing the procedure that fits the mechanism. A tight tendon repair on a muscle that cannot pull does little; a brow sling on a patient with a perfectly good levator is more surgery than needed.
| Option | How it works | Best suited to |
|---|---|---|
| External levator advancement | Through a lid-crease skin incision, the stretched aponeurosis is reattached and tightened on the tarsal plate; height and contour are often adjusted with the patient awake and opening the eye | Aponeurotic ptosis with good levator function — the workhorse adult operation, and can be combined with removal of excess skin |
| Müller muscle-conjunctival resection (MMCR) | Performed from the inside of the lid with no skin incision; a measured strip of Müller's muscle and conjunctiva is removed to shorten the lifting mechanism (described by Putterman and Urist in 1975) | Mild to moderate ptosis with good levator function and a positive phenylephrine test |
| Frontalis sling (brow suspension) | A sling of silicone, synthetic material or the patient's own fascia links the lid to the brow muscle, so raising the brows lifts the lid | Poor levator function — most often congenital ptosis, and some myogenic and neurogenic cases |
| Oxymetazoline 0.1% eye drops | An alpha-adrenergic agonist that stimulates Müller's muscle, giving a modest temporary lift of around a millimetre or two on average; approved by the US FDA in 2020 for acquired blepharoptosis in adults | Mild acquired ptosis in adults who want a non-surgical, daily option; not a treatment for neurogenic or congenital ptosis |
Illustrative visualisation of direction and rough relative magnitude only — not pooled effect sizes. See References for the pivotal oxymetazoline trial data and surgical series.
In the pivotal randomised trials behind the oxymetazoline approval, pooled by Slonim and colleagues in JAMA Ophthalmology in 2020, treated eyes showed a statistically significant improvement in superior visual field and in MRD1 compared with vehicle drops, with an effect that was real but modest. It is best understood as a temporary pharmacological lift for mild cases, not an equivalent of surgery.
Section 06 — Children
In a child, the worry
is not the lid.
It is the developing vision.
Congenital ptosis usually comes from a levator muscle that developed with fibrous, poorly contracting tissue, so levator function is often reduced and the lid may lag on downgaze. Most children with mild congenital ptosis see normally. The concern is amblyopia — a “lazy eye” that develops because the visual brain is not getting a clear image during the critical early years.
Ptosis can cause amblyopia in two ways: directly, when the lid covers the pupil and blocks the visual axis, and indirectly, when lid pressure on the cornea induces astigmatism that blurs one eye more than the other. That is why children with ptosis need a full eye examination including refraction, and why a lid covering the pupil in an infant is treated as more urgent than the same droop in an adult. Where surgery is needed and levator function is poor, a frontalis sling is the usual choice.
A woman in her forties who has worn rigid gas-permeable contact lenses for twenty years notices that her right upper lid sits lower than the left in photographs. Her MRD1 is 1.5 mm on the right and 4 mm on the left, levator function is 14 mm on both sides, the right lid crease is higher than the left, the pupils are equal and her eye movements are full. Nothing worsens with sustained upgaze.
Everything points to aponeurotic ptosis: a healthy muscle with a tendon that has slipped from the tarsus, a pattern repeatedly associated with long-term lens insertion and removal. A positive phenylephrine test would make her a candidate for either MMCR or external levator advancement; the choice between them comes down to surgeon preference and whether excess skin also needs removing.
Section 07 — After Eye Surgery
Ptosis after cataract
or other eye surgery.
A lid that sits lower after cataract, glaucoma or retinal surgery is a recognised and well-described phenomenon. It is usually attributed to stretching of the levator aponeurosis by the lid speculum that holds the eye open, combined with postoperative lid swelling, local anaesthetic injection and, in some techniques, a traction suture under the superior rectus muscle.
Much of this early droop improves over weeks to months as swelling settles. Where it persists beyond roughly six months, it behaves like any other aponeurotic ptosis and is assessed and repaired the same way. Surgeons sometimes minimise speculum stretch and lid manipulation for this reason, particularly in patients who already have a borderline lid position before surgery.
levator excursion
MRD1 (lower bound)
repairing post-surgical ptosis
Section 08 — FAQ
Frequently asked questions
about ptosis.
Ptosis (blepharoptosis) is a drooping of the upper eyelid so that it sits lower than normal over the eye. It happens when something weakens the system that lifts the lid: the levator muscle, its tendon (the levator aponeurosis), the small sympathetically driven Müller's muscle, or the nerves that supply them. It can affect one or both eyes and may be present from birth or develop later in life.
The most common cause in adults is aponeurotic ptosis, where the levator tendon gradually stretches or loosens from the tarsal plate with age, long-term contact lens wear, eye rubbing or previous eye surgery, while the muscle itself remains healthy. Less common causes include third nerve palsy, Horner syndrome, myasthenia gravis, muscle diseases such as chronic progressive external ophthalmoplegia, and lid masses. Excess upper lid skin (dermatochalasis) can mimic ptosis without the lid margin itself being low.
Seek same-day medical care if ptosis appears suddenly together with double vision, a larger pupil on the affected side, severe headache, or neck or face pain, or if it comes with a smaller pupil on the same side. These patterns can indicate a third nerve palsy from an aneurysm, or Horner syndrome from a carotid artery dissection. Ptosis that varies through the day and worsens with fatigue, especially with double vision, should be assessed for myasthenia gravis.
MRD1, the margin-reflex distance 1, is the distance in millimetres from the upper eyelid margin to the light reflex on the centre of the cornea while the patient looks at a penlight. In most adults it is around 4 to 5 mm. Clinicians also measure levator function, which is how far the lid travels from looking fully down to fully up with the brow held still; normal is around 15 mm. MRD1 describes how much the lid droops, and levator function guides which operation is suitable.
For mild acquired ptosis in adults, oxymetazoline 0.1% eye drops, approved by the US FDA in 2020, can give a modest temporary lift of around a millimetre or two by stimulating Müller's muscle. The effect lasts hours and the drops are used daily. They do not treat neurogenic or congenital ptosis. Ptosis caused by myasthenia gravis is treated medically. For moderate to severe or long-standing ptosis, surgery remains the definitive treatment.
The main operations are external levator advancement, which tightens and reattaches the stretched tendon through a lid-crease incision; Müller muscle-conjunctival resection, performed from inside the lid for mild to moderate ptosis with good levator function and a good response to phenylephrine drops; and frontalis sling surgery, which links the lid to the brow muscle when levator function is poor, as in many children with congenital ptosis. The choice depends mainly on levator function and the cause of the ptosis.
Yes. A drooping lid after cataract or other eye surgery is a recognised complication, usually attributed to stretching of the levator aponeurosis by the lid speculum, postoperative swelling and local anaesthetic injection. Much of this improves over weeks to months. If it persists beyond about six months it is assessed and repaired like any other aponeurotic ptosis.
References & Evidence Base
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citations.
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