Analysis of Using I125 Radiolabeling for Quantifying Protein on Contact Lenses

PURPOSE: To investigate the accuracy of I(125) radiolabeling to quantitatively determine the deposition of protein onto various commercially available contact lens (CL) materials. METHODS: Commercially available silicone hydrogel and conventional hydrogel CL materials were examined for times ranging from 10 s to 1 week. Adsorption of free I(125) was measured directly for the CL. The use of dialyzing labeled proteins and/or using NaI to compete with free I(125) uptake was investigated as ways to minimize effects due to free I(125). RESULTS: At all time points and with all lens materials, there was 0.3 μg/lens or greater of apparent mass attributable to free I(125) uptake. Dialyzing labeled proteins significantly reduced free I(125) uptake for all materials investigated. The benefit of using dialyzed protein was most prominent at shorter times, as free I(125) is continuously generated over time. Using NaI can reduce free I(125) uptake for some lens materials, but this is shown to directly affect protein deposition on some materials. CONCLUSIONS: Periodic replenishment of incubation solutions with freshly dialyzed labeled protein to limit free I(125) generation is recommended, but the incorporation of NaI onto the buffer solution is not. Irrespective of the exact procedure to limit free I(125) uptake, extra steps must be performed to quantify the amount of I(125) adsorbed onto contact lens materials, to determine thresholds of confidence with respect to the actual protein deposition that occurs.