ArticlesRandomised trial of effectiveness of second eye cataract surgery
Introduction
During the past 10–15 years there has been an increasing rate of cataract surgery in both the USA and the UK with the result that cataract extraction has become an extremely common surgical procedure.1, 2 This increase is partly due to demographic trends: in an increasingly elderly population there is an inevitable increase in the number of people with cataracts since the prevalence of cataracts rises with age.3, 4, 5 Also, in the past few years there have been major advances in the surgical and anaesthetic techniques used in cataract extraction, including the introduction of phacoemulsification and the advent of the increasingly widespread practice of local anaesthesia for day-case surgery. These changes have meant that many more patients with cataracts are potentially suitable for surgery, and as a result surgeons have adopted more liberal criteria when deciding whether or not to operate.1, 6
Balanced against this rising demand for cataract surgery, concerns over health-care expenditure have resulted in pressure to limit purchasing budgets. In an environment in which cataract operations may be rationed, the benefits of removing a cataract from the second eye have been called into question. In the USA the estimated cost of cataract surgery for 1991 was US$3·4 billion,7 and with second eye cataract surgery rates in the USA of 30–45%, the matter has been labelled a “billion dollar per year issue”.8 In the UK, about a third of cataract operations are done on second eyes.9
The effectiveness of cataract surgery per se is well established.1, 10, 11 Most of the studies have expressed effectiveness as the percentage of eyes (first or second) in which monocular tests of visual function (Snellen acuity) improve postoperatively. More recent investigations have included subjective outcome measures.12, 13, 14, 15, 16 Despite the fact that second eye cataract removal is widely practised, only a few studies have specifically investigated the benefits of second eye surgery in the context of everyday viewing with both eyes open.1, 8, 12, 17 Poor or absent binocular vision, as a result of reduced vision in one eye, may represent a handicap to visual function in a general sense. Furthermore, in the absence of binocular function, normal stereoscopic depth perception is not available. In a small study Kwapiszeski and colleagues showed an improvement in stereoacuity following surgery on monocular cataract.18 It is also known that in certain circumstances patients with monocular cataract may have binocular inhibition and binocular rivalry, which may adversely affect visual function and actually make vision with both eyes open worse than monocular vision with the better eye alone.19, 20 An abnormal Pulfrich phenomenon (disturbed motion perception) has been observed in patients with unilateral cataract, and this may further disturb visual perception in a moving visual environment.21
Although evidence does suggest that surgery for a second eye cataract may be beneficial, the few studies on this subject have the fundamental weaknesses of observational evaluation. The limitations of surgical research are well known, both in terms of willingness to undertake randomised trials at all,22 and the weakness of the trials that are done.23 The general objective of this study was to assess an established surgical procedure in a way that both satisfied the basic tenet of trial methodology, and which took account of the patient's own perception of visual function.
In this pragmatic trial24 it was possible to take advantage of the waiting period for surgery. Because this period is greater than the period during which the outcome of surgery becomes known, it is possible to randomise the timing of treatment rather than the nature of treatment to create a set of controls.
Section snippets
Patients
The trial recruitment ran from Feb 1, 1994, to April 30, 1995. During this time, eligible patients were obtained from all those listed for second eye cataract surgery at the Bristol Eye Hospital. Eligibility was defined as: awaiting second eye cataract surgery at the Bristol Eye Hospital; unilateral cataract and uncomplicated contralateral pseudophakia with corrected Snellen visual acuity of at least 20/40 in the pseudophakic eye; the absence of other visually significant ophthalmic pathology
Results
A total of 2330 patients were listed for cataract surgery at the Bristol Eye Hospital during the recruitment period. 807 (34·6%) patients were listed for second eye cataract surgery, of whom 350 (43·4%) were eligible for recruitment into the trial (figure). The commonest reason for ineligibility was coexistent ocular disease (eg, agerelated maculopathy, diabetic retinopathy, and glaucoma). 208 (59·4%) were randomised, 105 to the expeditedsurgery group and 103 to routine waiting time (control
Discussion
Concerns over health-care expenditure have resulted in a challenge to the established clinical practice of second eye cataract surgery after successful surgery in the first eye.8 There is little evidence supporting the benefit of secondeye cataract surgery,1 and where such evidence does exist, the research methodologies upon which it is based are observational or of limited power.8, 12, 17, 18 We report the main outcomes of a randomised controlled trial with adequate power to show the benefits
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