Sir,

I read the article by Kodjikian et al1 with interest. It is important to understand factors that influence the incidence of post-cataract endophthalmitis and sharing audit data is a useful way to achieve this. I wish to question the manner in which the data were analysed and the conclusions drawn.

There were essentially 3 disparate groups: group A, ECCE+PMMA lens; group B, phako+PMMA lens and group C, phako+foldable lens. Group B had a threefold higher incidence of POE than group A and the lack of statistical significance could easily be a type 2 error from the smaller number of patients in group A. Lack of statistical significance should not be interpreted as indicating that the groups are homogeneous and different groups should not be amalgamated to artificially lower P-values.

The authors discount the timing of surgery as relevant by comparing the first 4 years (1326 procedures) with the second 6 years (4511) on the basis of the frequency of surgical techniques used during these periods. Comparing six cases in the first 5 years with two in the second half of the study period gives a more accurate picture.

Other factors distinguishing the groups should also be investigated. It seems probable that group B was operated upon at a time when surgeons and theatre staff were learning a new technique. Were operating times longer during the learning period? Did techniques of cleaning and sterilisation alter over this time?

It is clear from this study that the incidence of POE was higher when a PMMA lens was used with phakoemulsification in the early days of this technique. The results obtained with ECCE and PMMA lenses were excellent with an incidence of POE of 0.1% and no patients were found having a final vision below 6/12 because of endophthalmitis. Once the new technique had been mastered and phako with foldable lenses became the norm, the results were at least as good. As the authors state the actual role of IOL material on POE is not established by this retrospective study, but we can be reassured that modern techniques are good.