Dr Graeme Young looks at the diameter of modern soft contact lenses, whether they meet their specifications and how they change with temperature
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In a typical population, corneal diameters vary by about 1.5mm,1 whereas the range of diameters on offer with daily disposable lenses is relatively narrow - 13.8 to 14.3mm. In fact, all but a few designs are labelled as 14.2mm. However, previous work has shown that measured diameter does not always correspond to labelled diameter because of the effects of pH, osmolarity and temperature. In particular, raising the temperature of the lens from room to eye temperature can have a significant effect.2-3
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