Electron microscopic features of never-worn soft contact lenses: deposits or artifacts?

Since scanning electron microscopy (SEM) is commonly used to evaluate hydrophilic lens deposits, it is important to know what artifacts are induced by the various techniques used to process the lenses. We performed scanning electron microscopy (SEM) using never-worn lenses with hydrations from 38.6% to 71%. Each lens was taken from its vial of factory-sealed, sterile-preserved saline and processed for SEM examination using liquid CO2, freon critical point drying, or air drying with or without alcohol dehydration. The lenses revealed abnormal surface structures occasionally resembling deposits reported on worn soft contact lenses. Varying degrees of gas pockets and surface wrinkling were seen. Individual polymers and lens hydration reacted differently to the various techniques of processing. Of the four methods evaluated, air drying without alcohol dehydration induced the least artifacts.