Post‐operative endophthalmitis and IOL material

Abstract

Editor, We wish to thank Drs Kodjikian, Burillon and Freney for their valuable comments regarding intraocular lens (IOL) material and its relation to postoperative endophthalmitis (POE) described in the paper ‘Endophthalmitis following cataract surgery in Sweden. The 1998 National Prospective Survey’ (Montan et al. 2002a). One of the findings of this study was that acrylic lenses were significantly less associated with POE than polymethylmethacrylate (PMMA) and hydrogel lenses. In contrast to what the writers of the letter claim, we did not conclude that acrylic is a less permissive material for POE. On the contrary, the conclusion of our paper states that our data in this regard ‘should be interpreted with much caution’. The reason for this caution is obvious: detailed data regarding a number of parameters with possible relevance for POE were simply not available through the register form for the control group. Kodjikian et al. are thus perfectly right in their criticism regarding the lack of information on a number of factors that might alter the risk of postoperative infection, such as the exact design and property of the IOL (not only the optic material), the presence of any putative innate propensity for developing infection in the operated patient, and, factors we perceive as highly essential, the prophylaxis regime and perioperative complications. These shortcomings were also thoroughly addressed in the discussion section of the paper. We nevertheless think it is interesting to address the issue of IOLs in relation to POE in this crude form, as previous studies have identified increased associations between certain IOL materials and POE (Menikoff et al. 1991; Bainbridge et al. 1998; Montan et al. 1998). We have continued to publish data from the Swedish National Cataract Register (NCR) (Wejde et al. 2005). We believe that if there were important differences in the adhesiveness of bacteria to various lens materials, divergent patterns of POE frequencies would be found in a consistent manner. In such an event it would be feasible to perform a posthoc investigation in order to pinpoint the exact lens design and to screen for various risk factors in the disease group. We did not feel that such an assessment was warranted in the present paper because our forthcoming studies will be based on a far more extensive material. All the lens types cited in our first paper in Acta were in fact compared with one another and a consequent lowering of the p-value was performed, as is clearly stated in the methods section. The only statistically significant results found were between acrylic lenses and the two other materials mentioned above. Therefore, only the comparisons between acrylic lenses and these other types were presented, but the actual POE frequencies for all IOL types were reported in a table and could easily be calculated with a statistical program by anyone interested. Finally, Kodjikian et al. wish to have our comments on a previously reported finding that heparinized PMMA IOLs may protect against POE, which is at odds with the present results. This may be explained by the fact that the previous results were obtained in an era with a higher POE rate than is found presently in our country (0.25% versus the present incidence of 0.06–0.1%) (Montan et al. 2002b). In addition, the unfoldable heparinized PMMA IOL was not used as a back-up lens at the time, which seems to be the case presently, in that surgeons today use a rigid heparinized lens in the event of a capsular break, a perioperative complication which in itself may predispose to infection. The tendency to develop POE is certainly multifactorial and only large scale, prospective studies with meticulous protocols will be able to establish whether any IOL is more protective than others against POE. In the meantime, we believe that the ongoing POE registration through the NCR may provide some useful information in this respect.