CATARACT SURGERY

Cataract surgery is the most commonly performed procedure undertaken in the NHS, and one of the most successful. In most cases it is performed as a day case procedure, usually under local (topical) medication.

HOW IS CATARACT SURGERY PERFORMED?

Cataract surgery involves removing the cloudy lens within the eye by phaco-emulsification, which involves using a vibrating probe that dissolves and sucks out the lens. The phacoemulsificating probe is inserted into the front of the eye via micro-incisions in the peripheral cornea. The micro-incisions are not visible to the naked eye and usually heal up without requiring any stitches. Once the lens is removed, the supporting 'capsule' bag is left in place. Any remnants of soft lens material are removed using an aspirating probe, making sure not to damage the capsular bag. An artificial lens is then inserted via the same incision into the bag. By folding the lens and using an injector to insert the lens into the eye, there is no need to enlarge the micro-incision. Once the lens is in the bag, any viscoelastic gel used during the procedure is aspirated. Finally, a small amount of antibiotic is injected into the eye at the end of the procedure.

HOW IS THE ARTIFICIAL LENS CHOSEN?

The artificial intraocular lens power is usually calculated to give the patient good distance vision. The patient will usually require a glasses prescription for reading. Other types of intraocular lens are available that can correct for astigmatism (toric lenses) or that can give bifocal or multifocal vision. One can also request a different refractive outcome, for example if you are used to having monovision with one eye for distance, and one for reading.

It is always best to discuss your choice of lens and refractive outcome with your surgeon well before the day of surgery.

WHAT ABOUT USING LASERS FOR CATARACT SURGERY?

Recently, it has become possible to carry out some of the stages of the cataract surgery, such as the incisions, the opening of the capsular bag and the dividing up of the cataract, using a femtosecond laser.

It is expected that this enhancement may increase predictability and reduce complication rates. It is likely that in very experienced hands these advantages may be negligible when compared with conventional cataract surgery and at this stage most cataract surgeons do not offer this technique. Femtosecond phaco surgery is available through Moorfields Private and will soon be available through Moorfields NHS as part of a clinical trial comparing this new technique with conventional phaco-emulsification surgery.

WHAT DOES POST-OPERATIVE CARE INVOLVE?

A four-week reducing course of topical steroid and a shorter course of topical antibiotic is required. Most patients see well within a day of the surgery but it sometimes may take up to a week to achieve very good distance vision. Patients will usually be advised to attend their optometrist after 6 weeks to get a new refraction, which may only be required for a reading prescription.

Patients can usually restart most of their daily activities from within a week of their surgery.

WHAT ARE THE POSSIBLE COMPLICATIONS?

Cataract surgery has a very low complication rate, with about a 1 in 1000 risk of severe complication (infection/endophthalmitis and suprachoroidal haemorrhage) that can cause loss of vision.

More commonly, in about 1 in 100 cases, there may be complications at the time of surgery such as rupture of the capsular bag. This may require a longer procedure or more than one procedure to put things right.

Rupture of the capsular bag may require an additional procedure, called an anterior vitrectomy, at the time of the cataract surgery. This enables vitreous jelly to be removed from the front of the eye. If done correctly, this will allow the intraocular lens to be placed in a safe and stable position. Rupture of the capsule with vitreous loss is associated with an increased risk of infection, retinal detachment and of blurring of vision due to fluid at the macula (macular oedema). These risks will be reduced with an appropriately performed anterior vitrectomy and in most cases, one can expect the same outcome as if no complication had been encountered.

Sometimes all of the natural lens cannot be removed at the time of surgery or the artificial intraocular lens cannot be inserted, so an additional procedure needs to be undertaken at a later date to remove the remaining lens material or to insert the artificial lens.

Retinal detachment may occur after cataract surgery, and this will require an additional surgical procedure to put right.

Whilst these complications are unfortunate and hopefully will be avoided, in experienced hands they should not result in an adverse outcome as long as the complication is addressed appropriately. Recovery time, however, will be much longer than for uncomplicated surgery with best vision taking weeks or months to be achieved rather than just days.

Cystoid Macular Oedema (CMO), which can cause poor post-operative vision, may occur after complicated cataract surgery or in eyes with a previous history of inflammation/uveitis. In some cases it can occur spontaneously without any obvious predisposing cause. In most cases it will either resolve spontaneously or after an appropriate course of anti-inflammatory treatment, with no long term adverse effects to vision.

In the longer term, 1 in 10 cataract surgery patients will develop a fogging behind their intraocular lens called 'posterior capsular opacification'. This can give symptoms of blurring, as though the cataract has grown back. It can be reversed very simply using a laser treatment called laser capsulotomy. This is performed at a slit lamp under topical anaesthesia.

CATARACT AND GLAUCOMA

Whilst the success rate and complication rate discussed here refer to normal circumstances, the situation may be more difficult in eyes with both cataract and glaucoma.

VISUAL PROGNOSIS

Eyes with established visual loss from glaucoma may not experience as impressive an improvement in vision after cataract surgery as non-glaucoma patients.

This is because the visual loss from glaucoma is irreversible and will remain after the cataract has been removed.

Furthermore, in advanced glaucoma it is possible that the degree of glaucoma damage may worsen leading to deterioration in vision or even loss of vision (wipeout), although the latter is extremely rare.

The prognosis for cataract surgery in glaucoma patients can therefore be considered as guarded.

In most cases there will be a significant improvement but occasionally, if there is very bad glaucoma, the vision may stay the same or very rarely get worse, even in uncomplicated cases.

ARE GLAUCOMA EYES AT INCREASED RISK OF COMPLICATION DURING CATARACT SURGERY?

Cataract surgery in glaucoma eyes, particularly eyes that have previously undergone glaucoma surgery, can be much more difficult and prone to complication than routine cataract surgeries.

The following situations are more commonly encountered in glaucoma cases:

• Very big eyes

• Very small eyes

• Shallow anterior chambers (as seen in angle closure)

• Weak supporting zonules (as seen in pseudoexfoliation),

• Small pupils (as seen in pseudoexfoliation or following the long-term use of pilocarpine),

• Low IOP

• High IOP

All of these circumstances may lead to an increased likelihood of intraoperative complication.

Often cataract surgery in glaucoma patients will take longer than normal, as additional manipulations and care has to be taken to prevent complication and to ensure the optimal outcome. An experienced glaucoma surgeon will be used to operating on such eyes routinely and will be able to anticipate any potential problems.

DOES CATARACT SURGERY HELP LOWER IOP

Lens extraction can be an effective treatment for lowering the IOP. This is certainly the case for eyes with primary angle closure, where lens extraction may be offered even if there is very little by way of cataract. In these cases, it is likely that surgery will be offered if the IOP is high and there is a high risk of visual damage if the angle closure is not completely reversed.

The IOP may also be lowered in eyes with open angles and so this can be a beneficial treatment. Furthermore, the new MIGS devices are usually combined with cataract surgery to try and maximise and lengthen the IOP-lowering effect of cataract surgery, although long-term outcomes are not yet known.

CATARACT AND GLAUCOMA SURGERY

As glaucoma and cataract are both diseases of ageing, they frequently co-exist. However, generally speaking combining cataract surgery with trabeculectomy surgery is avoided as the risk of long-term failure through scarring is higher than when carrying out the procedures separately.

Cataract surgery in eyes with previous trabeculectomy is associated with a 30-40% chance of the trabeculectomy failing, meaning that one will need to restart IOP-lowering drops or to have further intervention such as needling.

The risk of failure is probably much lower in eyes with pre-existing tubes.

Experienced glaucoma surgeons are perhaps best equipped to perform cataract surgery in patients with previous glaucoma surgeries or with advanced glaucoma. At the very least, cataract surgery performed by non-glaucoma specialists should be undertaken in close consultation with the patient's managing glaucoma specialist.

NICK STROUTHIDIS