Randomised trial of effectiveness of second eye cataract surgery

Summary

Background

The effectiveness of cataract surgery on one eye is well established, but concerns over health-care expenditure have called into question the value of cataract surgery on the second eye. We examined the effects of second eye surgery in terms of patient perceptions as well as through visual acuity, contrast sensitivity, and stereoacuity tests.

Methods

208 otherwise healthy patients awaiting second eye cataract surgery were recruited into our randomised trial. At randomisation participants were allocated expedited surgery (planned to take place within 6 weeks) or routine surgery (routine waiting time, 7–12 months). Assessments were made at randomisation and again at review after about 6 months. Eight primary trial outcomes consisted of four questionnaire items and four visual function tests, done with both eyes open.

Findings

Traditional clinical tests of success in cataract surgery (visual acuity and contrast sensitivity) showed only slight differences in binocular vision in favour of the expedited-surgery group. There were major benefits for the expedited-surgery group in terms of reported visual symptoms and effects on quality of life. At review, differences in self-reported vision related difficulties between the two groups ranged from 11% (95% CI 4·4–17%, activities) to 30% (19–41%, reading). Stereoacuity was better in the expedited surgery group, the difference between the groups for the proportions with stereoacuity of 3000 s of arc or worse was 58% (47–69%).

Interpretation

This trial has shown that there is a clear benefit from 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.