RECENT ADVANCES IN CATARACT SURGERY

by Mr Mark T Watts FRCS, FRCOphth Consultant Ophthalmic Surgeon, Wirral Hospitals Trust Honorary Lecturer in Ophthalmology, University of Liverpool

Cataract surgery can now be performed on a day-case basis, with improved visual results and a shorter recovery time. In this article, the author describes the new surgical techniques, and the way in which these affect the role of the general practitioner.

Recent changes in the surgical approach to cataract surgery, and the widespread use of day-case surgery under local anaesthesia, have revolutionised patients' experience of the most common intra-ocular operation. In particular, the technique of emulsification of the lens during its removal has not only improved visual results, but has considerably shortened the period of post-operative recovery. These changes have led to alterations in criteria for referral for surgery, and early post-operative care is being transferred from hospital to the general practitioner.

Small-incision cataract surgery

The major innovation that has changed cataract surgery is small-incision surgery, whereby a cataractous lens is removed through a 3.5 mm incision in either the sclera or cornea. With this technique there is minimal, or no, post-operative astigmatism, and therefore a less distorted final image for the patient. The need for complex spectacle prescriptions is eliminated. In addition, because the wound is so small, it stabilises very rapidly. It is therefore unnecessary to wait for months after surgery until such stability has been achieved before prescribing glasses. Indeed, there is often no need for bifocal or multi-focal glasses.

In order for the lens to be removed through such a small incision, it has to be emulsified. This is done using an ultrasonic probe inserted through the wound. This probe contains, at its centre, a fine, hollow, needle vibrating at 48 kHz. The emulsified lens can be aspirated through the lumen of the needle. A rubber sleeve surrounding the needle provides for irrigation of fluid into the eye, in order to prevent its collapse as aspiration is undertaken, and also to cool the vibrating needle. The technique is known as phaco-emulsification Following removal of the lens, it is then possible to insert a soft, folding silicone lens through the small incision. The lens expands in the capsular bag previously occupied by the cataractous lens to provide a new refracting lens The incision is self-sealing, and therefore requires no suturing. Not only does this eliminate a potent cause of induced astigmatism, but it also avoids the problem of loose or degraded sutures irritating the eye some months or years after surgery. In addition, a self-sealing wound increases the safety of surgery in patients who may, for whatever reason, be unable to lie still but who are unsuited to general anaesthesia.

Local anaesthesia

Local anaesthesia for eye surgery is not new, but in recent years a better understanding of the anatomy of the orbit, the development of better disposable needles, and improved techniques of administering such anaesthesia have made local anaesthesia for cataract surgery safer and more comfortable for the patient. In many units, the use of general anaesthetic for cataract surgery is now the exception, with both patients and surgeons preferring local anaesthetic techniques.

Instillation of anaesthetic drops is usually followed by the injection of either lignocaine or bupivacaine into the orbital space. This not only paralyses the eye, but renders it anaesthetic and unable to see. While previously it was usual to administer retrobulbar anaesthesia into the cone of muscles behind the eye, there has recently been a trend to using "peri-bulbar" anaesthesia. In this technique, the anaesthetic is given peripheral to this cone of muscles instead, thus avoiding the risks of causing haemorrhage behind the eye, perforating the eye, damaging the optic nerve, or injecting into the dural space around the nerve.

This technique has rendered the use of local anaesthetic much safer, both to the eye and to the patient overall. A further refinement has been to inject trans-conjunctivally, rather than through the skin, making the injection more comfortable.

The use of such minimally invasive anaesthetic techniques has extended the range of patients to whom surgery can be offered. Patients who might previously have been considered too frail to endure either general anaesthetic or heavy sedation can now be treated.

All patients operated on under local anaesthesia are carefully monitored throughout, and an intravenous cannula is inserted in case of emergency. Resuscitative cover should always be immediately available, and it is normal practice for an anaesthetist to be present. In the rare event of a patient becoming over anxious and unable to co-operate, intravenous sedation can then be administered. It is necessary to use a head-drape to ensure asepsis, but this is lifted free of the patient's mouth, and air is piped under the drape. An assistant holds the hand of the patient to provide reassurance and a method of communication for the patient if there is any anxiety.

Selecting the lens implant

Routine implantation of an intra-ocular lens following removal of the cataract improves surgical results dramatically, preventing the need for "bottle-bottom" glasses following cataract surgery, with all their attendant visual distortions. However, early attempts at lens implantation were frequently complicated by unexpected changes in refraction post-operatively. In particular, a number of patients were left with inequalities in power between the two eyes.

By measuring the axial length of the eye from cornea to retina using ultrasound, and assessing the refractive power of the cornea by studying corneal reflections, the likely post-operative refraction of the eye following insertion of an intra-ocular lens implant can be calculated. By selecting differing powers of intra-ocular lens implant, the desired post-operative refraction can be chosen prior to surgery.

It is now routine practice to undertake such "biometry" of the eye before surgery. Many units combine these measurements with a pre-operative assessment of the patient's general health and social circumstances, and a discussion and explanation of the operation with the patient and relatives.

Day-case surgery

Day-case surgery is becoming increasingly widespread, and cataract surgery is well suited to it. Most patients prefer to spend a minimal time in hospital, and units that offer day-case surgery have found enthusiastic patient acceptance.

As with all day-case surgery, selection of patients is crucial, and in-patient management is still preferable for some. It is important that the patient is accompanied home after the procedure and is in telephone contact with the hospital in case of emergency. When in doubt, suitability will be discussed with the general practitioner, who has knowledge of his or her patients and their social circumstances.

Patients requiring or preferring general anaesthesia can also be offered day-case cataract extraction, and the development of new short-acting anaesthetic agents, and the use of the laryngeal mask have made this a safe technique.

Changing referral criteria

The increased safety of cataract surgery has enabled surgeons to reduce their threshold for operating. Many people who might previously have been regarded as having too slight a lens opacity to warrant surgery are now being operated on with good results.

Advances in psychometric testing of vision demonstrate that the Snellen test, although still useful, is not always an accurate assessment of visual impairment. Some patients with a cataract may demonstrate good Snellen acuity, but experience severe problems in dim lighting, or excessive glare in sunlight, reducing their vision to levels significantly below that required for driving.

Patients complaining of such symptoms should not therefore be dismissed just because they have, for example, 6/12 or 6/9 Snellen acuity. In cases of doubt, a refraction and slit-lamp examination by an optician may help to identify early cataract not easily seen with an ophthalmoscope.

The easiest way of detecting cataract in the surgery is to examine the "red reflex" of the eye with an ophthalmoscope held 1 m from the patient's eye. Light directed through the pupil from the ophthalmoscope is normally reflected back by the retina to give a circular red reflex. In dense cataract, the reflex is absent, but in earlier cataract, the opacity in the lens is demonstrated as an imperfection in the round circle of red light seen. Dilation of the pupil with tropicamide may help in this assessment. Symptomatic patients in whom cataract is identified should be referred.

Patients may be told by their optician that they have cataract, even when their vision is perfect. Not all cataracts cause visual symptoms, particularly in the elderly, whose vision may be reduced by other causes. Many elderly patients still fear the diagnosis of cataract, having known friends or relatives go blind because of the disease. It is important to emphasise to patients who may be anxious about this that the diagnosis of cataract does not always imply progressive visual deterioration culminating in surgery.

Post-operative care

Because patients are discharged early, they may present to their general practitioners with worries or questions about their post-operative care that would previously have been answered in hospital.

Post-operatively, most ophthalmologists prescribe a course of topical steroids, sometimes combined with mydriatic drops, to dilate the pupil for the first few weeks after surgery. A plastic shield may be given to the patient to wear at night, to protect the eye from injury during sleep.

Restrictions on physical activity previously included no bending over, washing of the hair, straining, and so on. These have been considerably reduced by the advent of small, self-sealing incisions. It is wise for patients to avoid touching the eye, and swimming should be avoided for at least 2 weeks. Driving can be resumed as soon as vision is recovered.

Patients can now attend opticians for spectacles much earlier. With large incisions, it was often necessary to wait for 2 or 3 months before astigmatism had settled, but small incisions induce minimal or no astigmatism and are stable much earlier. The ophthalmologist will tell patients when they can be refitted with glasses, but generally this can be done 2 to 3 weeks after surgery.

Depending on the patient's refraction, he or she may need to wear glasses for distant sight, near sight, or both, in order to achieve best acuity. Patients may wear their old glasses pending refitting, although vision may be limited. Visual rehabilitation is rapid, but patients who are deliberately made slightly myopic by the choice of implant power, may feel that their vision is not good until new glasses are fitted.

Conclusion

Cataract surgery has advanced significantly and has changed patients' experience, outcome and expectations. It has also changed referral criteria and post-operative care by their general practitioner. Hospitals and general practitioners need each other's help in best managing such changes, and close liaison between the two is vital.