Why does vitrectomy cause cataracts?

What does vitrectomy remove from the eye?

Vitrectomy is keyhole surgery that removes the vitreous, the clear gel that fills the back of the eye, so the surgeon can work on the retina. It is used to repair a retinal detachment, close a macular hole, peel an epiretinal membrane, clear blood that is not absorbing, for example from diabetic eye disease, and for selected people with persistent floaters. The vitrectomy surgery page describes the operation itself.

Vitrectomy probe →1Infusion line →2Light pipe →3Retina →4+

1. Vitrectomy probe2. Infusion line3. Light pipe4. Retina

The gel does not grow back. At the end of the operation the space is filled with a clear salty fluid, which the eye gradually replaces with its own fluid. Sometimes a gas bubble or silicone oil is left inside for a while to support the retina as it heals. The natural lens sits directly in front of this space, so whatever fills it bathes the back of the lens.

How does removing the gel cause a cataract?

The best-supported explanation is oxygen. Oxygen enters the inside of the eye mainly from the blood vessels of the retina. In a healthy eye, vitamin C held in the vitreous gel reacts with that oxygen as it spreads forwards, so very little is left by the time it reaches the lens. The lens is built to work in this low-oxygen setting.

When the gel is removed, fluid can circulate freely between the retina and the back of the lens. In measurements taken during surgery on 69 eyes, oxygen levels beside the lens were about 9 mm Hg with the gel in place and about 70 mm Hg once it had been removed. It stays higher than normal for a long time afterwards: eyes that had already had a vitrectomy still had raised oxygen levels when they were measured at a later operation.

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Oxygen is thought to damage the proteins in the centre of the lens, the nucleus, which gradually turns yellow-brown and hazy. Several separate observations point the same way:

• Eyes whose gel has naturally turned watery with age tend to have more of this central cataract.
• People who have many sessions of high-pressure oxygen treatment for other medical conditions can develop the same type of cataract.
• In eyes where diabetic retinopathy had reduced the retina's blood supply, which is thought to leave less oxygen inside the eye, the lens changed little after vitrectomy. In a large US registry, diabetes, and laser treatment to the retina during the vitrectomy, were both linked to a lower chance of later cataract surgery.

Most of the oxygen research comes from one research group, and oxygen may not be the whole story. It is, however, the explanation that fits the evidence best. A cataract after vitrectomy is an expected effect of removing the gel; it does not by itself mean the lens was injured during the operation.

What kind of cataract forms, and what will I notice?

Usually a nuclear cataract, in which the centre of the lens slowly becomes yellow-brown and cloudy. It is the most common type after vitrectomy. Clouding just inside the back surface of the lens, called posterior subcapsular cataract, also occurs, and in one large series was linked to silicone oil and younger age. The article on types of cataracts shows how these differ, and what causes cataracts covers the other common causes.

Front viewSide view

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The change is usually gradual. Vision becomes blurred or foggy, colours look duller or more yellow, and bright lights can dazzle. A nuclear cataract can also change the focus of the eye and make it more short-sighted, so glasses that suited you soon after the vitrectomy may stop working well.

Because the retina has also been treated, it is not always obvious how much of the blur comes from the lens and how much from the retina. An examination and an OCT scan of the retina help to separate the two before any decision about cataract surgery.

How soon does the cataract appear?

In older adults, often within a year or two. In a UK database covering 27 hospitals, about half of eyes had cataract surgery within a year of vitrectomy, about seven in ten within two years and three-quarters within three. A US registry of more than 180,000 eyes with a natural lens estimated that 46% had cataract surgery within two years. Both count operations, so the number of eyes with some clouding is higher still.

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An older study followed 100 people after epiretinal membrane surgery for an average of about two and a half years. By the end, 80 of the operated eyes had a significant nuclear cataract or had already had it removed, compared with 24 of the same people's other eyes.

Timing still varies from person to person. Some cataracts become troublesome within months; others take several years. Having some cataract before the vitrectomy makes a later cataract operation more likely.

Does age make a difference?

Yes, a large one. Before about 50, the lens usually changes slowly after vitrectomy. In a study comparing 28 people under 50 with 28 people over 50 who had the same operation with a gas bubble, 7% of the younger group developed significant lens clouding over about two years, compared with 79% of the older group. Another series found that nuclear cataract progressed about six times faster from age 50 onwards, at a similar rate in every older decade. The US registry found the highest risk of cataract surgery in people in their 50s and 60s.

Fifty is not a switch, though. Younger people can still develop a cataract, particularly after retinal detachment repair with a long-acting gas bubble. In one small study of adults aged 15 to 45 after detachment repair, most developed some cataract, and the central type was more common over 35. When younger eyes do develop cataract, the posterior subcapsular type is relatively more common. A younger person's natural lens still helps with focusing up close, which is one reason to keep it while it remains clear.

Do gas bubbles and silicone oil add to the risk?

Yes. A gas bubble is often used after detachment or macular hole surgery to hold the retina in place while it heals. In a series of 301 eyes, the central cataract progressed about 60% faster when gas had been used.

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Where a bubble rests against the back of the lens, it can also cause a fine, feathery clouding. This usually clears within a week or two. Lying face up lets the bubble float forwards against the lens, and specialists advise against lying on your back while gas is in the eye because it may also speed up cataract formation. The head positions you are given after surgery keep the bubble where the retina needs it and away from the lens. The vitrectomy recovery guide explains positioning and the other precautions while gas is present.

Silicone oil is used for more complex detachments and may stay in the eye for months. Cataract develops in most oil-filled eyes that still have their natural lens, in up to about nine in ten with long enough follow-up, and sooner than after gas. Oil resting against the lens tends to cause clouding at its back surface.

Front viewSide view

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What else affects the risk?

• Why the vitrectomy was done. In the US registry, cataract surgery was more likely after vitrectomy for retinal detachment, macular hole or epiretinal membrane than after other vitrectomies.
• Cataract already present. Eyes with some cataract before surgery were about 1.8 times as likely to have cataract surgery within two years.
• More than one vitrectomy. Eyes that have had vitrectomy before have higher oxygen levels inside the eye at a later operation.
• How much gel is removed. In floater surgery that deliberately left a layer of gel behind the lens, fewer than 1 in 10 eyes of people under 50 and about 4 in 10 of people over 50 went on to cataract surgery within about two years. That approach suits floaters, not most retinal repairs, and it has not been compared directly with fuller surgery.
• Lens touch. Rarely, an instrument touches the lens during surgery and damages it directly. In the UK database this was recorded in about 1 to 2 in 100 eyes with a natural lens.

Can anything reduce the risk?

Not reliably. No eye drop, tablet or supplement has been shown to prevent cataract after vitrectomy.

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A few practical steps help at the margins. If you have a gas bubble, follow the positioning advice and avoid lying on your back. The choice of gas or oil, and how much gel is removed, is decided by what the retina needs; repairing the retina safely comes before protecting the lens. Researchers are developing gel-like replacements for the vitreous, but these are still experimental.

For most people over 50 with a natural lens, the realistic plan is to expect a cataract and to decide in advance how and when it will be treated.

Should cataract surgery be done at the same time?

It depends on your age, how much cataract is already present, the retinal problem and how much you still rely on your own lens for close focus. Removing the cataract during the vitrectomy, a combined operation often called phacovitrectomy, avoids a second trip to theatre. Doing them separately, months apart, keeps a younger person's natural focusing for longer and lets the cataract operation be planned once the retina has settled.

For macular holes and epiretinal membranes, a review of ten studies found similar vision and similar complication rates whether the two operations were combined or done separately, although most of the studies were of low quality. Compared with routine cataract surgery, the glasses prescription after combined surgery is slightly less predictable, with a tendency to end up a little short-sighted; the review comparing combined with separate operations did not find a clear difference in prescription. When silicone oil is used in an eye that still has its natural lens, combining is often considered because a cataract is so likely.

Combined cataract and retinal surgery: time-lapse

Combined cataract and retinal surgery: time-lapse

A time-lapse of cataract surgery and vitrectomy in one operation. It shows real eye surgery.

Watch on YouTube →

The page on combined cataract and retinal surgery explains the joint operation, and the article on whether to have the two operations together or separately walks through the decision in more detail.

What happens when the cataract needs treating?

The cloudy lens is removed and replaced with a clear lens implant, as in routine cataract surgery. There is no fixed waiting period; surgery is usually considered when the cataract affects your vision or the surgeon's view of the retina. The operation is planned a little differently, because without the gel behind it the lens is less supported and the eye behaves differently during surgery.

Vision usually improves once the cloudy lens is replaced. How much depends on the retina: in a UK study of more than 2,000 eyes, vision improved significantly, but on average ended about two lines lower on the letter chart than in eyes without a previous vitrectomy, and weakness of the lens supports and dropped lens fragments were more common. There are no randomised trials of cataract surgery after vitrectomy, so this advice rests on observational studies. The article on cataract surgery after vitrectomy explains what is different about the operation.

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Other questions about cataract after vitrectomy

Where can I read more?

When do I need urgent help after vitrectomy?

A cataract develops gradually over months and is not an emergency. A sudden change is different. Contact your ophthalmologist urgently, or attend an emergency department, if after vitrectomy you notice a sudden drop in vision, severe or increasing pain, increasing redness, new flashes of light, a shower of new floaters, or a shadow or curtain across part of your vision. These can be signs of infection, raised eye pressure or a retinal detachment. Do not wait for your next appointment.