QUANTITATION OF TOTAL PROTEIN DEPOSITS ON CONTACT-LENSES BY MEANS OF AMINO-ACID-ANALYSIS

Purpose. This study was done to characterize and quantify the protein deposits on work contact lenses and to measure the residual deposits after extraction in 2% sodium dodecyl sulfate and the total protein deposits on worn vifilcon, atlafilcon, and tefilcon lenses (Food and Drug Administration Types IV, II, and I, respectively). Methods. Contact lens extracts were separated with gel electrophoresis, and the amount of protein was estimated after silver staining and densitometry. To determine the residual deposits, the contact lenses were hydrolyzed, and amino acid analysis was carried out by reverse-phase high-performance liquid chromatography after precolumn derivatization with phenylisothiocyanate. Refinement of the hydrolysis conditions was undertaken to minimize interference by the lens polymers. Results. The extraction removed only approximately 25% of the protein deposits. Mild hydrolytic conditions, 20 hr in 6 N HCI at 105-degrees-C, were found to cause minimal polymer interference. Of the 350, 10, and 20 mug of protein typically determined on whole vifilcon and tefilcon lenses, the polymers were estimated to account for 4, 0.5, and less than 0.4 mug respectively. Conclusions. Hydrolysis of worn contact lenses with subsequent amino acid separation can be applied to determine the total protein deposits without the uncertainty inherent in extraction of the deposits.