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Second cataract surgery

Surgery to remove cataracts has moved on apace, so that now many of these operations are done as day cases. Cataract surgery works, and is a major benefit to most people, generally elderly, who need it. Cataracts are usually bilateral, and there has apparently been some argument that if surgery on one eye is successful, then surgery on the other is not needed. A randomised trial of second cataract surgery from Bristol refutes that [1].


The usual waiting time for second cataract surgery in Bristol was seven to 12 months. The study randomised patients needing second cataract surgery (without other ocular comorbidity) to either expedited surgery for 98 patients (within six weeks) or routine waiting time for 94 patients. Before randomisation and about six months after surgery detailed assessments were carried out. These included four primary outcomes of binocular visual function, and four daily living outcomes asking about:


Patients in the two groups were similar at randomisation. All eight primary outcomes were highly significantly better in the group with expedited surgery - with statistical significance generally at the 1 in 10,000 level. The proportion of patients having poor binocular vision (stereoacuity 3000 or worse) was dramatically lower at 12% in those who had expedited surgery compared with 70% in those still waiting for surgery.

The numbers needed to treat for the four outcomes describing daily living are shown in the Table. Second eye cataract surgery prevented eyesight interfering with life quite a lot or a great deal in one of every four patients having the operation.

Primary outcomes of daily living in trial of second cataract surgery
Outcome Percent with surgery Percent without surgery NNT (95% CI)
At least some difficulty reading normal print 6 36 3.5 (2.5 to 5.5)
Eyesight preventing activities most or all the time 0 11 9.4 (5.8 to 24)
Below average overall vision 0 18 5.5 (3.8 to 9.9)
Eyesight interfering with life quite a lot or a great deal 1 26 4.1 (3.0 to 6.5)


The daily living outcomes represented responses which were at the harsh end of possible answers, and appear to be sensible representations of real life. The questions were arrived at through an intensive process to make sure that they made sense and that patients could make sense of them. This was a well done trial which answers the question: second cataract eye surgery does benefit patients.


  1. DA Laidlaw, RA Harrad, CD Hopper et al. Randomised trial of effectiveness of second eye cataract surgery. Lancet 1998 352: 925-9.

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