In short. Faces are not symmetrical before surgery, and repairing one lid can move the other. That is why both sides are sometimes planned together.

Key points

  • The two lids are driven together by a shared signal from the brain, which tries to keep them level.
  • When one lid is held down and the other is not, the effort is distributed between them.
  • Raise the drooping lid, and the signal that was keeping both of them working changes, so the untreated lid can settle into a slightly different position.

Most patients arrive believing their two lids are the same and one of them has changed. In practice, faces are asymmetrical before any operation, and a droop is often superimposed on a difference that has been there for years. Understanding that before the operation is easier than discovering it afterwards.

Asymmetry is the starting point, not the result

A measurement of both lids at the first visit usually shows a difference that predates the droop, sometimes in the brow, sometimes in the position of the lid edge, sometimes in the shape of the eye itself. Patients are often unaware of these differences, because the brain adapts to a face it sees every day, and a photograph taken from the other side shows them more clearly than a mirror does. A photograph from ten years earlier is the simplest way to show this. Where the difference has always been there, the aim is not to make the two identical, because that would mean operating on a lid that has not changed. It is to correct what has changed and leave the rest alone, and to say clearly what will remain uneven.

Why the second lid can move on its own

The two lids are driven together by a shared signal from the brain, which tries to keep them level. When one lid is held down and the other is not, the effort is distributed between them. Raise the drooping lid, and the signal that was keeping both of them working changes, so the untreated lid can settle into a slightly different position. It is not a complication of the operation so much as a consequence of the way the lids are wired together.

Why both sides are sometimes operated on

Where that shared signal is likely to move the untreated lid, planning both sides in advance is more predictable than correcting one and reacting to the result. Both may be treated in a single operation, or the two may be staged so that the response of the first can be seen before the second is set. Where the difference between the two lids is small and the droop is clearly on one side, treating one side and leaving the other is a legitimate plan, and it is worth hearing the reasoning either way.

Be careful when

  • Only one lid is measured, when both are going to be discussed.
  • A promise is made that the two sides will end up identical.
  • You are not told what will remain uneven after the operation.

What to hold on to

The useful question is not whether the two lids will match, but what the plan assumes about the lid that is not being operated on. A plan that names the asymmetry it is leaving alone, and that says what it expects the other lid to do, has been thought through. A plan that treats the operation as though only one lid were involved has left something out.

Related reading

Frequently asked questions

If only one lid droops, why would both be operated on?

Because the two lids are linked. Raising one can change the position of the other, so a patient who has a single side repaired can find that the untreated side has shifted and the two no longer match. Where that is likely, planning both sides gives a more predictable result than correcting one and watching the other.

How much asymmetry is normal after the operation?

Some is normal, and it is judged after the swelling has gone rather than in the first weeks. The two sides heal at different rates, and the swelling is rarely equal. A difference that is still present at several months is a different question from one that is present on the tenth day.

Should the two sides be operated on in one session or separately?

Either can be reasonable. Doing both together gives a single recovery and lets the surgeon compare the two sides at the time of the operation. Separating them lets the response of the first lid be seen before the second is set, which is useful when the droop is changing or when the plan is uncertain.

Risks & Limitations

  • The lid can be left sitting higher or lower than intended. Both are recognised outcomes of an operation that adjusts position, and a further operation to set the height is part of this surgery rather than a failure of it.
  • An eye that does not close fully, or that feels dry, gritty or watery, is the complication watched for most closely here. It is more likely in a lid that was already dry, which is why the tear film is examined before anything is planned.
  • The two lids are rarely symmetrical before surgery and can remain uneven after it. Where one lid is repaired, the other may change position on its own, which is why both sides are sometimes planned together.
  • Blurred vision in the first days is usually the ointment and the swelling rather than the eye. A change in vision that persists, or double vision, is assessed rather than waited out.
  • Bruising, swelling, a gritty feeling and a lid that sits higher than expected in the first weeks are the normal course rather than complications, and settle over weeks to months.
  • A scar in the lid crease, or above it after a suspension operation, matures over months and does not disappear.
  • No operation in this area can promise a particular lid height, and the final height is judged in months rather than weeks.

When to Seek Care

  • Sudden drooping of one or both lids, especially with double vision, difficulty swallowing, slurred speech or weakness elsewhere: seek emergency care immediately rather than an appointment.
  • Severe eye pain, sudden loss of vision, or an eye that becomes rapidly swollen and tense after an operation.
  • A lid that is not closing at all, or an eye that is exposed and painful when you try to sleep.
  • Bleeding from the wound that does not stop with gentle pressure, or a wound that opens.
  • Fever with spreading redness, warmth or discharge around the eye.
  • Dryness, a gritty feeling or watering that is getting worse rather than settling.

References & Further Reading

  • American Society of Plastic Surgeons (ASPS) — procedure and safety guidance
  • National Institute for Health and Care Excellence (NICE, UK) — relevant guidance
  • Cochrane Library — systematic reviews
  • Chinese Medical Association Plastic Surgery Branch — clinical guidance

Medically reviewed by Tongchun Mao, MD (毛彤春), Deputy Director & Head of Aesthetic Surgery. Last reviewed: 19 September 2026.

This page is patient education, not medical advice, and it does not cite individual studies. Discuss your own case with a qualified clinician. To arrange an assessment at Chongqing West District Hospital, see Contact & Consultation.