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Secondary implants after cataract surgery.

Until 10 years ago good vision after the extraction of a cataract was achieved by using either spectacles or contact lenses. The results in terms of visual acuity were excellent, but many patients were unhappy with having to wear spectacles and the magnification or distortion that these produced. Contact lenses provided a wide visual field and were effective even in patients in whom only one lens had been removed. Nevertheless, patients sometimes became intolerant of contact lenses, and many elderly patients found it difficult to cope with the necessary hygiene regimens. Permanent wear soft lenses were easier to tolerate, but there was an appreciable incidence of corneal infection. Since then the techniques of cataract surgery have been modified considerably. Surgeons now prefer to use the extracapsular method, which leaves behind the posterior lens capsule to form a support for an implant in the posterior chamber. Intracapsular surgery is still carried out widely, however, often combined with the insertion of a lens in the anterior chamber whose supporting feet lie in the drainage angle between the iris and cornea. In good hands both these methods provide excellent visual results with few of the problems of other forms of aphakic correction. Not surprisingly, patients who have had their cataracts removed some years ago may inquire whether they too might have an implant as a secondary procedure. In general, patients who are considered for secondary implants have had an intracapsular extraction. This may have been a conventional procedure or may have been necessary because of injury causing dislocation of the lens, preventing the use of the extracapsular technique. The argument against secondary intraocular lens surgery is the risk of harming a healthy aphakic eye. Nevertheless, if the visual acuity is excellent but the patient is having problems with binocular vision, distortion of the visual fields, or tolerance of contact lenses then a secondary implant is advisable. Some early objections were owing to the poor quality control of intraocular lenses for the anterior chamber. Complications from uveitis together with glaucoma and hyphaema were common after secondary implantation. Recent series, however, have shown that the incidence of complications is now low, particularly since the introduction ofviscoelastic materials for anterior segment surgery. To ensure success preoperative assessment is all important; in particular, the evaluation of any mishaps that may have occurred during the original cataract extraction is essential. Most important is the assessment of the corneal endothelium with a slit lamp and, if need be, with a specular microscope. Endothelial counts of fewer than 1000 cells/mm2 are a contraindication,2 for there may be a continuing loss of endothelial cells after operation due to the mobility of the implant and an accompanying uveitis (D J Spalton and J McGill, personal communication). This is especially important when the surgeon is considering secondary implantation in patients aged under 50. The objections to secondary implantation vary from centre to centre, but great care must always be taken with any patient who has diabetes, glaucoma, or uveitis or who is under 50. If the original cataract was due to trauma then very careful assessment must be carried out before the implantation of a secondary lens. Above all it is most important to discuss the possible complications with the patients and, as they are often elderly, with their relatives. Any intraocular procedure may be bedevilled by postoperative cystoid oedema of the macula, which leaves the patient with poor central vision that does not always respond to treatment. This may happen in a perfectly healthy eye but is more likely if there were complications at the original operation or if the patient has had inflammatory eye disease in the past or is diabetic. Despite all the possible hazards, however, secondary intraocular lens implantation is now well established. It has proved so dependable that it is an acceptable alternative for patients who are unhappy with aphakic spectacles or contact lenses.3