Sir,

We read with interest Rimmer et al's letter1 published in January suggesting a higher incidence of Hydroview lens (Bausch and Lomb) calcification in those implanted between late 2000 and mid-2001. The main cause of opacification was thought to be silicone in the lens packaging.2, 3 As the packaging did not change between 1997 and 2001,2 Rimmer et al's observations suggest that other aetiological factors might be involved.

A study set up at Bristol assessed the impact of Hydroview opacification on vision (Central and South Bristol Research Ethics Committee Ref 05/Q2006/163).4 We re-evaluated the data from this study to investigate the associations of opacification with patient, surgical, and lens-related factors. Data were gathered through a review of medical records, patient interview, and examination.

Data from 215 patients who had Hydroview lenses implanted in Bristol were analysed: 125 had clear lenses, 89 had evidence of opacification, and 1 lens could not be assessed. No statistically significant association was demonstrated between opacification and any of the patient- (Tables 1 and 2) or surgery-related factors (Table 3) tested. However, this is likely to be a result of the small number of patients at subgroup analysis level.

Table 1 Association between lens opacification and ocular pathology
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Table 2 Association between lens opacification and systemic pathology
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Table 3 Association between lens opacification and surgical factors
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There was a marked association of opacification with certain runs of consecutive lens serial numbers (Table 4). Serial numbers relate only to the order in which the lenses are manufactured and are sequential. Our study will have selection bias, as all patients had surgery over a similar time period and those symptomatic would be more likely to enrol. There will be a high number of certain runs of serial numbers and a high number of opacified lenses. However, variation in the proportion of lenses opacified (3–79%) across the serial numbers tested strongly suggests an association between opacity and certain runs of serial numbers.

Table 4 Association between lens opacification and serial number
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Although these data must be viewed with respect to the context, ie, as a retrospective observation rather than as prospective evidence, they do question the supposition that the sole cause for opacification was the silicon gasket. The findings support a manufacture-related cause over a patient- or surgical-related cause for opacification. Although no conclusions can be drawn about the nature of this unknown aetiological factor, our data pinpoint it within a narrow time frame of manufacture.