Deposits originate from tear film components (as tears evaporate or by chemical attraction). lens handling, cosmetics and the external enviroment. Problems associated with deposits include discomfort (mechanical effects), dryness and fluctuating vision (decreased lens surface wetting). Deposits also contribute to the development of inflammatory responses, and have been associated with infection.
The main types of deposits on soft contact lenses are protein and lipid. Both invariably form on all soft contact lenses, usually in combination, can be are visible on soft contact lenses within minutes of insertion. Deposition is affected by individual variation, lens types, wear mode, care systems and the wearing enviroment.
When not associated with inflammation, significant deposition reduces wear time and satisfaction by:
- Increasing discomfort (dry, scratchy, gritty).
- Hazy vision which may improve immediately after blinking but then deteriorates prior to the next blink.
Protein – an intially colourless film of unneven thickness that gradually thins, hardens and loses transparency with ageing (denaturation). The level of protein deposited varies substantially between individuals and lens types.
Lipid – minute, droplet-like deposits loosely bound to the contact lens surface. Excess lipid will decrease the ability of the tears to spread over the lens surface, leading to poor wettability (dryness and blurred vision typically toward the end of the day).
Frequent lens replacement is the only way to prevent protein deposit related problems.
Deposits can be reduced but not completely removed by proper care and maintenance procedures.
Protein removal treatments (tablets or solutions) will reduce but not totally remove protein.
Surfactant cleaning will remove most surface lipid.
Lenses should be replaced when deposits cause patient symptoms and produce visible signs even without symptoms. For example, upper lid redness and/or roughness (papillae).