Which group of soft contact lens material is most likely to get lens deposits?

• A. Group 1: low water content, non-ionic
• B. Group 2: high water content, non-ionic
• C. Group 3: low water content, ionic
• D. Group 4: high water content, ionic

Answer: (D)

Deposits form mainly from tear film proteins and lipids, and how much deposits depends on material properties like surface charge and water content. An ionic surface carries a net charge that attracts oppositely charged tear proteins (for example, lysozyme), so electrostatic attraction pulls proteins onto the lens. High water content increases the lens’s permeability to water-soluble components, allowing more tear components to diffuse into and adhere to the lens matrix. Put together, a lens that is both high in water content and ionic provides the strongest combination for protein and other tear deposits to accumulate. In contrast, non-ionic surfaces lack the electrostatic pull, and low water content reduces uptake of tear components, so they deposit less.