How Cataract Surgery Works: Phacoemulsification Step by Step
By Pauline Driscoll | Medically reviewed by Mr Lewis Pereira, FRCOphth
Published May 4, 2026 · Last reviewed May 12, 2026 · 2 min read
Key takeaways
- The standard technique is phacoemulsification, which uses ultrasound to break up the cloudy lens through a tiny self-sealing incision.
- The incision is around 2 to 3 mm and usually self-sealing, so most cases need no stitches.
- An opening is made in the front of the lens capsule, and the cloudy lens is broken up and removed in fragments.
- A folded intraocular lens is inserted into the empty capsule, where it unfolds and stays permanently.
- The operation is a day case under local anaesthetic and typically takes about 15 to 30 minutes per eye.
Cataract surgery works by phacoemulsification: through a tiny self-sealing incision of around 2 to 3 mm, an ultrasound probe breaks the cloudy lens into fragments and removes them, then a folded clear intraocular lens is inserted into the lens capsule where it unfolds and stays permanently1. It is a day case under local anaesthetic, with the operation itself typically taking about 15 to 30 minutes per eye2.
This is the deep dive into the method behind cataract surgery. If you want the patient experience instead, see what cataract surgery feels like, and to know how to prepare see the cataract assessment.
Step one: numbing and preparation
The eye is numbed with local anaesthetic, most often numbing drops and sometimes a small injection, so you are awake but feel no pain2. Drops are also used beforehand to dilate the pupil, opening a clear path to the lens.
You lie flat, the area around the eye is cleaned, and a small frame holds the eyelids gently open so you do not need to worry about blinking. When my turn came I was braced for the worst, but the numbing was so complete that I felt only mild pressure and saw soft, shifting lights.
Step two: the incision and opening the capsule
A tiny self-sealing incision of around 2 to 3 mm is made at the edge of the cornea, small enough that most cases need no stitches1. The surgeon then makes a precise circular opening in the front of the lens capsule, the thin clear bag that holds the lens.
This opening is the doorway to the cloudy lens inside. The capsule itself is kept, because it will become the stable home for the new implant3.
Step three: breaking up and removing the lens
This is the heart of phacoemulsification: an ultrasound probe is passed through the incision and uses sound energy to break the cloudy lens into tiny fragments, which are then gently suctioned away1. The empty capsule is left in place, ready to receive the implant.
It is a remarkably controlled process for something happening inside the eye, and it is the reason the operation is so quick and the wound so small. The standard nature of this technique is reflected in clinical guidance, which treats phaco as the routine approach4.
Step four: inserting the new lens
A folded intraocular lens (IOL) is passed through the same tiny incision and inserted into the empty capsule, where it unfolds and settles into position2. Because the lens is folded, it fits through the 2 to 3 mm opening and then opens out inside the eye.
The implant stays permanently, taking over the focusing job of the old lens. Which lens is used depends on choices made beforehand, covered in choosing a lens for cataract surgery. The self-sealing incision usually closes without stitches, the eye is shielded, and you go home the same day to begin cataract surgery recovery.
References
- Cataract surgery, American Academy of Ophthalmology. ↩
- Cataract surgery, NHS. ↩
- Understanding cataracts: patient information, Royal College of Ophthalmologists. ↩
- Cataracts in adults: management (NG77), NICE. ↩
Common questions
What is phacoemulsification?
Phacoemulsification, often shortened to phaco, is the standard modern technique for cataract surgery. A fine probe uses ultrasound energy to break the cloudy lens into tiny fragments, which are then gently suctioned out through a tiny self-sealing incision of around 2 to 3 mm. Once the cloudy lens is removed, a folded clear intraocular lens is inserted into the empty lens capsule, where it unfolds and stays permanently.
Does cataract surgery hurt?
No, cataract surgery is not usually painful. It is done under local anaesthetic, most often numbing eye drops and sometimes a small injection, so the eye is numb and you are awake but feel no pain. You may be aware of lights, gentle pressure and water on the eye, but not sharp sensations. The numbness means the eye stays comfortable throughout the short operation.
How big is the incision in cataract surgery?
The incision is small, around 2 to 3 mm, and is usually self-sealing, which means most cases need no stitches. The small size is one reason recovery is quick and the eye settles within days to weeks. The folded intraocular lens is designed to pass through this tiny opening and then unfold inside the eye.
Are you awake during cataract surgery?
Yes, in almost all cases you are awake, because the surgery is done under local anaesthetic rather than general anaesthetic. The eye is numbed so you feel no pain, and you simply lie still and look towards a light. Being awake is safer for most people and means you can go home the same day as a day case.
What is the lens capsule and why does it stay?
The lens capsule is the thin, clear bag that naturally holds your eye's lens. During surgery the surgeon opens the front of this capsule, removes the cloudy lens from inside it, and then places the new intraocular lens into the same capsule. Keeping the capsule gives the implant a stable, natural home in the eye. The back of the capsule can later cloud, which is treated separately with a laser.
How long does the operation itself take?
The operation itself typically takes about 15 to 30 minutes per eye, often quoted as around 20 minutes, although you will be at the hospital or clinic longer for preparation, dilating drops and recovery. It is done one eye at a time, with the second eye usually treated a few weeks later if both need surgery.
Written by Pauline Driscoll. Medically reviewed by Mr Lewis Pereira, FRCOphth.
Our guides are written from personal experience and reviewed by a qualified clinician for accuracy. Read our editorial policy.
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