Ptosis (pronounced “TOE-sis”) is a drooping of the upper eyelid that makes one or both eyes look partially closed. In a normal eye, the upper lid sits about 4 to 5 millimeters above the center of the pupil. In ptosis, that gap shrinks, and the lid drops low enough to cover part of the iris or even the pupil itself. The result is an asymmetric, heavy-lidded, or sleepy appearance that can range from barely noticeable to severe.
The Core Visual Sign: A Drooping Upper Lid
The hallmark of ptosis is straightforward: one upper eyelid hangs lower than the other, or both lids hang lower than they should. When ptosis affects only one side, the asymmetry is usually what people notice first. The affected eye looks smaller or more closed compared to the other. In mild cases, the lid edge drops just a couple of millimeters, partially covering the top of the iris (the colored part of the eye). In moderate to severe cases, the lid can sag low enough to cover the pupil entirely, blocking vision.
If you’re trying to spot ptosis in the mirror or on someone else, focus on where the upper lid margin sits relative to the pupil. Normally, only a tiny sliver of the upper iris is hidden by the lid. When the lid creeps down to cover more of the iris, or starts to overlap the pupil, that’s ptosis.
Compensatory Signs You Might Not Expect
People with ptosis often develop unconscious habits to see past the drooping lid, and these secondary signs can be just as visible as the droop itself. The most common is a raised eyebrow on the affected side. The forehead muscle kicks in to lift the brow, which pulls the eyelid up slightly. Over time, this creates persistent forehead wrinkles or a noticeably arched brow on one side.
Children with ptosis frequently tilt their chin upward so they can peek out below the sagging lid. This “chin-up” head posture is sometimes the first thing a parent notices, even before the eyelid droop catches their attention.
How It Looks in Children vs. Adults
Congenital ptosis, the kind present from birth, has a distinct appearance. The eyelid crease (the natural fold line in the upper lid) is often faint or completely absent, giving the lid a smooth, flat look. When the child looks downward, the affected lid doesn’t follow the eye as smoothly as the normal lid does. It tends to lag behind, remaining higher than expected on downgaze. This “lid lag” is one of the clearest visual clues that ptosis has been present since birth rather than developing later. In severe cases, the lid can obstruct enough of the pupil to interfere with visual development and lead to amblyopia, commonly known as lazy eye.
Age-related ptosis looks different. It develops gradually as the tendon connecting the lid muscle to the eyelid stretches or thins over the years. The eyelid crease is still present but often sits higher than normal, creating a deep, hollowed-out fold in the upper lid. The skin above the crease may appear thin or translucent. Many older adults describe feeling like their eyelids are “heavy” before they ever notice a visible droop in the mirror.
Ptosis vs. Excess Eyelid Skin
Not every droopy-looking eyelid is true ptosis. A condition called dermatochalasis, where loose, redundant skin accumulates on the upper lid, can mimic the appearance of ptosis closely. The skin folds over the lid margin and may even hang over the lashes, creating a hooded look that seems identical to a drooping lid.
The key difference is where the lid margin itself sits. In dermatochalasis, the actual edge of the eyelid stays in a normal position relative to the pupil. The skin is just draping over it. You can test this roughly by gently lifting the eyebrow into its normal position. If the “droop” disappears, the issue is likely excess skin or a sagging brow rather than true ptosis. In many cases, the two conditions coexist, with both a low lid margin and excess skin contributing to the heavy appearance.
When Ptosis Signals Something Neurological
Most ptosis is either present from birth or develops gradually with age, and neither type is dangerous on its own. But certain patterns of drooping signal a neurological issue that needs prompt attention.
In Horner syndrome, a condition caused by disruption of a specific nerve pathway, ptosis appears alongside a noticeably smaller pupil on the same side. The combination of a drooping lid and a constricted pupil, with the other eye’s pupil remaining normal size, is a distinctive pattern. Some people with Horner syndrome also notice reduced sweating on the affected side of the face.
Ptosis that fluctuates throughout the day, worsening as muscles tire in the evening and improving after rest, can be a sign of myasthenia gravis, an autoimmune condition affecting muscle-nerve communication. In this case, the droop may shift between eyes or worsen on both sides over the course of hours.
Sudden, severe ptosis on one side accompanied by a dilated (enlarged) pupil and difficulty moving the eye is a medical emergency. This pattern can indicate a problem with the nerve that controls most eye movements, sometimes caused by pressure from an aneurysm.
Mild, Moderate, and Severe: Gauging the Degree
Doctors classify ptosis severity by measuring how far the lid margin sits from the center of the pupil. In a normal eye, that distance is 4 to 5 millimeters. Mild ptosis brings the lid edge closer, covering just the top portion of the iris. You might notice it in photographs but not during casual conversation. Moderate ptosis drops the lid to the upper edge of the pupil, giving the eye a distinctly half-closed look. Severe ptosis covers the pupil partially or completely, visibly obstructing the line of sight and making the affected eye look nearly shut.
In severe unilateral cases, the drooping is dramatic enough that the light reflecting off the center of the cornea is no longer visible on the affected side because the lid simply covers too much of the eye. This is one of the clearest visual indicators clinicians use, and it’s something you can observe in a well-lit mirror: if you can’t see a pinpoint of light reflected in the center of your eye because your lid is in the way, the ptosis is significant.