Are Soft Silicone Hydrogel Contact Lenses More Compliant in a Warm, Hydrated Environment?

This study examined how temperature and hydration affect the mechanical and optical properties of silicone hydrogel contact lenses. Two materials, Definitive 74 and Unisil, were evaluated under room (24 °C) and physiological (35 °C) conditions. Both materials softened at higher temperature, with Definitive 74 showing a larger modulus drop (0.40 → 0.32 MPa) than Unisil (0.73 → 0.70 MPa). Finite element modeling showed that increased compliance at 35 °C significantly influenced refractive power, especially when the lens base curve differed from corneal radius by >5 %. The work demonstrates that soft lenses are more compliant in warm, hydrated conditions, emphasizing the importance of physiologically relevant testing for accurate optical and comfort predictions.