Accurate Determination of Moisture Content of Soft Contact Lenses by Near-Infrared (NIR) Spectroscopy

Near infrared (NIR) spectroscopy is a rapid, non-destructive method for analysis of routinely measured products. NIR can eliminate lost time and lost product while improving real time quality control. The delicate properties of soft contact lenses require a minimal-contact method for analysis to avoid damage to the lens itself. NIR spectroscopy provides a quick and damage-free solution. Four sets of soft contact lenses with known moisture levels were analyzed by NIR spectroscopy. The spectra were analyzed for quantitative model development. Difficulties arose due to moisture loss by evaporation. However, with careful attention to testing procedures, a model was successfully developed and used to determine the embedded moisture levels in soft contact lenses with an error less than 1 %. Several methods were tested and evaluated based on accuracy, precision, experimental simplicity, and potential for lens damage.