Why Deposits Form
Every contact lens that sits on the eye is bathed in tear fluid. The tear film contains proteins, lipids, mucins, minerals, and cellular debris that naturally adhere to the lens surface and absorb into the lens matrix over time. This deposit accumulation is unavoidable during lens wear; the rate and type of deposition depend on the patient's tear composition, the lens material properties, and the care routine.
Deposits degrade visual quality, reduce comfort, and trigger inflammatory and allergic responses. Understanding the different deposit types and their material interactions allows practitioners to select appropriate lens materials and care regimens for each patient.
Types of Deposits
Protein Deposits
Protein is the most common type of contact lens deposit:
- Lysozyme is the predominant tear protein that deposits on lenses, accounting for the majority of protein accumulation
- Proteins initially adsorb in their native (folded) state but gradually denature (unfold) on the lens surface
- Denatured proteins are recognized as foreign by the immune system, triggering inflammatory responses including GPC
- Protein deposits appear as a hazy film on the lens surface and reduce optical clarity
Lipid Deposits
- Originate from meibomian gland secretions in the tear film
- Create a greasy, hydrophobic coating on the lens surface
- Cause blurred, "filmy" vision and difficulty wetting the lens
- More common on silicone hydrogel lenses due to their inherent hydrophobicity
- Resistant to standard surfactant cleaning; may require specific lipid-removing cleaners
Calcium Deposits
- Form as hard, white, translucent nodules on the lens surface, often called "jelly bumps"
- More common on high-water-content lenses where calcium can crystallize within the hydrated polymer matrix
- Cannot be removed by cleaning; lenses with calcium deposits must be replaced
- Feel rough to the patient and can cause corneal irritation
Mucin Deposits
- Mucins from the tear film combine with other deposits, particularly proteins
- Create a sticky coating that attracts additional debris
- More significant on lenses worn for extended periods
FDA Lens Material Groups and Deposit Tendencies
The FDA classifies soft contact lens materials into four groups based on water content and ionic charge:
| FDA Group | Water Content | Ionic Charge | Primary Deposit Type |
|---|---|---|---|
| Group I | Low (<50%) | Non-ionic | Minimal deposits overall |
| Group II | High (>50%) | Non-ionic | Some lipid, less protein |
| Group III | Low (<50%) | Ionic | Moderate protein |
| Group IV | High (>50%) | Ionic | Heavy protein deposition |
Group IV lenses attract the most protein because their ionic surface charge binds positively charged lysozyme, and their high water content allows protein to penetrate into the lens matrix. Group I lenses resist deposits the most effectively.
Factors Affecting Deposit Rate
- Lens material: As described by FDA group and silicone content
- Tear composition: Patients with lipid-deficient or protein-heavy tears deposit differently
- Wearing time: Longer daily wear and extended replacement schedules increase accumulation
- Care regimen: Inadequate daily cleaning allows deposits to build up and harden
- Environmental exposure: Smoke, dust, and cosmetics contribute external deposits
- Meibomian gland dysfunction: Abnormal lipid secretion increases lipid deposition
Consequences of Deposits
- Reduced comfort: Roughened surface increases friction and lid sensation
- Decreased visual acuity: Deposits scatter light and create irregular optical surfaces
- GPC: Denatured protein deposits trigger immune responses leading to giant papillary conjunctivitis
- Increased infection risk: Bacterial biofilms preferentially form on deposited surfaces
- Reduced oxygen permeability: Thick deposit layers can decrease the effective Dk/t of the lens
Management
- Shorten replacement schedule: The most effective way to manage deposits is to replace lenses before significant accumulation occurs
- Daily disposable lenses: Eliminate deposits entirely by discarding the lens daily
- Change material: Switch from a deposit-prone material to one better suited to the patient's tear composition
- Enzymatic cleaning: Weekly treatment with papain or subtilisin for patients on longer replacement schedules
- Rubbing during cleaning: The "rub" step in lens cleaning is significantly more effective at removing deposits than soaking alone
Key Takeaways
- Protein (lysozyme), lipid (meibomian secretions), and calcium ("jelly bumps") are the main deposit types
- FDA Group IV (high-water, ionic) lenses attract the most protein; silicone hydrogels attract more lipid
- Denatured protein deposits trigger GPC and increase infection risk
- Shorter replacement schedules and daily disposable lenses are the most effective deposit management strategies
- Calcium deposits cannot be removed by cleaning and require lens replacement