A comprehensive guide for IOL and contact lens manufacturers using Rotlex IOLA and Contest systems
Why Measurement Environment Matters
Intraocular lens (IOL) and contact lens manufacturers face a fundamental measurement decision every production day: should lenses be measured wet or dry? This choice directly impacts measurement accuracy, production throughput, regulatory compliance, and ultimately patient outcomes.
The difference between wet and dry measurement is not merely procedural-it reflects the physical reality of how ophthalmic lenses function. Hydrophilic IOLs with 18-38% water content exhibit different optical properties when hydrated versus dehydrated. Contact lenses designed for on-eye wear must be characterized in conditions that simulate their intended environment.
Rotlex measurement systems-including the IOLA 4C, IOLA MP, IOLA MFD for IOLs, and Contest 2 and Contest MP for contact lenses-are specifically engineered to handle both wet and dry measurements with identical precision. The IOLA MP, for example, can process up to 50 dry lenses or 12 wet lenses in a single automated cycle, while the Contest MP delivers 0.03 D repeatability across both measurement modes.
This guide provides production engineers, quality managers, and metrology technicians with step-by-step protocols for switching between wet and dry measurement configurations. Following these procedures ensures measurement consistency, prevents cross-contamination between modes, and maintains the 0.04 D repeatability that Rotlex systems deliver.
Understanding the Physical Basis for Wet and Dry Protocols
Material Behavior and Measurement Implications
Different lens materials require different measurement environments based on their physical properties:
Hydrophobic acrylic IOLs contain minimal water (typically less than 1% water uptake). These lenses can be accurately measured in dry conditions because their optical properties remain stable regardless of hydration state. Dry measurement offers faster throughput since no equilibration time is required.
Hydrophilic acrylic IOLs contain 18-38% water when fully hydrated. These lenses must be measured wet to reflect their actual in-eye optical performance. Measuring a hydrophilic lens dry would yield incorrect power values because the dehydrated lens has different refractive properties than the implanted lens.
Contact lenses vary widely in water content, from low-water RGP materials to high-water hydrogels exceeding 50% water content. The Contest 2 and Contest MP systems accommodate this range by supporting wet measurement in temperature-stabilized saline at 35°C to simulate in-eye conditions, as well as dry measurement for materials where hydration does not significantly alter optical properties.
Optical Path Considerations
When measuring lenses in liquid versus air, the optical path through the measurement system changes. Rotlex systems compensate for this automatically through:
ISO 11979-2 conversion algorithms built into IOLA systems translate measurements taken in the model eye (with physical cornea and appropriate medium) to equivalent in-eye performance values.
Four interchangeable physical corneas in the IOLA 4C system (ISO Model Eye 1, ISO Model Eye 2, aspheric, and spherical-aberration-free) enable manufacturers to select the measurement configuration that matches their regulatory requirements and clinical correlation needs.
Calibration profiles in Contest systems maintain separate calibration parameters for wet and dry modes, ensuring accuracy is preserved regardless of measurement environment.
Pre-Switching Preparation Checklist
Before switching between wet and dry measurement modes, complete the following preparation steps:
Environmental Verification
Temperature should be within the operating range of the specific system. The IOLA MP operates across 5°C to 45°C, with optimal measurement stability at 18-25°C. The MCT-3000 specifies 18-28°C with temperature stability of ±2°C recommended. Verify your laboratory conditions meet these requirements before any mode switch.
Humidity should remain within 30-70% RH (non-condensing) throughout the measurement session. Humidity fluctuations can affect both lens hydration state and optical surface quality.
Documentation Requirements
Record the following before initiating any mode switch:
Current date and time, operator identification, current measurement mode (wet or dry), reason for switching, last calibration verification date, reference lens verification results from current shift.
Equipment Inspection
Visually inspect all optical surfaces, lens holders, wet cells, and liquid handling components. Any contamination, scratches, or residue will affect measurement accuracy after the switch.
Confirm that all required accessories for the target measurement mode are available and clean:
For wet mode: appropriate wet cell, fresh saline or deionized water, clean holding fixtures
For dry mode: clean dry trays, appropriate dry lens holders, anti-static measures if required
Protocol A: Switching from Dry to Wet Measurement on IOLA Systems
This protocol applies to IOLA 4C, IOLA MP, and IOLA MFD systems when transitioning from dry IOL measurement to wet IOL measurement.
Step 1: Complete Current Dry Measurement Batch
Finish all pending dry measurements and export data before initiating the switch. Do not leave incomplete measurement sessions, as switching modes mid-batch can create data management complications.
Save current session data in your preferred format (TXT, Excel, or via API to your database system). IOLA systems support SQL Server, MySQL, and custom database integration with CFR 21 Part 11 compliant audit trails.
Step 2: Remove Dry Measurement Components
Power down the measurement cycle but keep the system in standby mode.
Remove dry lens trays from the IOLA MP loading area. The system accommodates up to 50 dry lenses per tray; ensure all lenses are removed and properly documented.
Remove any dry lens holders or fixtures from the measurement position.
Step 3: Clean Optical Surfaces
Using approved optical cleaning solution and lint-free wipes, clean:
The measurement window and any exposed optical surfaces
The lens positioning stage
Any contact surfaces that will interface with wet components
Allow surfaces to dry completely before installing wet measurement components. Residual moisture on dry-mode surfaces can cause measurement artifacts when switching back to dry mode later.
Step 4: Install Wet Measurement Configuration
Install the appropriate wet cell for your lens type and measurement requirements.
For IOLA 4C: Select and install the appropriate physical cornea from the four available options (ISO Model Eye 1, ISO Model Eye 2, aspheric, or spherical-aberration-free). Ensure the cornea is clean and properly seated.
For IOLA MP: Install the wet lens tray system designed to hold up to 12 wet IOLs. Verify proper seating and alignment.
Fill the wet cell with the appropriate medium: deionized water or balanced saline solution (BSS) depending on your measurement protocol and regulatory requirements. Ensure no air bubbles are present in the optical path.
Step 5: Prepare Measurement Solution
Solution preparation directly impacts measurement accuracy:
Temperature equilibration: Allow measurement solution to reach room temperature (18-25°C) before use. Temperature differences between solution and laboratory environment cause convection currents that degrade measurement stability.
Bubble elimination: Gently agitate the wet cell after filling to release trapped air bubbles. Even small bubbles in the optical path cause significant measurement errors.
Solution cleanliness: Use fresh solution for each measurement session. Particulate contamination accumulates in reused solutions and affects optical clarity.
Step 6: Software Configuration
Access the system software and navigate to measurement mode settings.
Select “Wet” or “Hydrated” measurement mode. The system will automatically load the appropriate calibration profile and conversion algorithms.
Verify that ISO 11979-2 conversion parameters are correctly configured for your selected model eye and measurement medium.
Confirm measurement parameters match your product specifications: power range, cylinder range, and acceptance tolerances.
Step 7: Verification Measurement
Before beginning production measurements, perform a verification sequence using a certified reference lens measured in wet conditions:
Place reference lens in wet cell, ensuring proper centration and no air bubbles
Perform three consecutive measurements
Calculate mean, range, and standard deviation
Acceptance criteria: Mean within ±0.04 D of certified value, range ≤0.04 D, standard deviation ≤0.02 D
Document verification results before proceeding. If verification fails, troubleshoot before beginning production measurements.
Step 8: Begin Wet Production Measurements
Once verification passes, begin production wet measurements. The IOLA systems deliver 4-second measurement time per lens with 0.04 D repeatability in wet mode.
Monitor the first several production measurements to confirm stable operation. Watch for any indication of air bubble formation, solution contamination, or temperature drift.
Protocol B: Switching from Wet to Dry Measurement on IOLA Systems
Switching from wet to dry measurement requires careful attention to moisture removal to prevent measurement artifacts.
Step 1: Complete Current Wet Measurement Batch
Finish all pending wet measurements and export data. Ensure complete documentation of the wet measurement session.
Step 2: Remove Wet Measurement Components
Remove all wet cells and liquid-containing components from the measurement area.
Drain measurement solution properly according to your facility’s waste handling procedures.
Remove physical cornea if applicable (IOLA 4C) and store according to manufacturer recommendations.
Step 3: Dry All Components Thoroughly
This step is critical for accurate dry measurements:
Remove all visible moisture using lint-free wipes
Allow components to air dry in a clean environment for a minimum of 15-30 minutes
For faster transition, use clean, dry compressed air to accelerate drying
Inspect all surfaces under adequate lighting to confirm complete dryness
Residual moisture on optical surfaces will cause measurement errors in dry mode. Take adequate time for this step.
Step 4: Install Dry Measurement Configuration
Install dry lens trays in the IOLA MP (capacity up to 50 dry lenses per cycle)
Install appropriate dry lens holders or fixtures
Verify all components are completely dry before placing production lenses
Step 5: Software Configuration
Switch software to “Dry” measurement mode
Verify measurement parameters are appropriate for dry measurement: the system may apply different conversion algorithms for dry versus wet measurements
Confirm tolerance settings match your dry product specifications
Step 6: Verification Measurement
Perform verification using a certified dry reference lens:
Place reference lens in dry holder with proper centration
Perform three consecutive measurements
Acceptance criteria: Mean within ±0.04 D of certified value, range ≤0.04 D
Document verification results. The IOLA series delivers identical 0.04 D repeatability in dry mode as in wet mode.
Step 7: Begin Dry Production Measurements
Once verified, begin production dry measurements. The IOLA MP processes up to 50 dry lenses per automated cycle, significantly increasing throughput compared to wet measurement batches of 12 lenses.
Protocol C: Wet/Dry Switching on Contest Systems for Contact Lenses
The Contest 2 and Contest MP systems measure contact lenses in both wet and dry configurations. The Contest 2 offers flexibility for R&D and QA laboratories with mixed wet/dry trays, while the Contest MP provides fully automated high-throughput production measurement.
Contest 2 Protocol: Switching to Wet Mode
Preparation:
Verify laboratory temperature is within 5°C to 45°C operating range (optimal: 22°C)
Prepare temperature-stabilized saline at 35°C for hydrated measurement simulating in-eye conditions
Confirm humidity is within 30-70% RH
Component Setup:
Install wet measurement cell appropriate for your lens diameter range
Fill with 35°C saline, ensuring complete bubble elimination
Allow system to thermally equilibrate (15 minutes recommended)
Software Configuration:
Select hydrated/wet measurement mode
The Contest 2 loads separate calibration profiles for hydrated mode automatically
Verify temperature monitoring shows stable 35°C
Verification:
Measure reference lens three times
Confirm repeatability ≤0.03 D
Document verification before production
Contest 2 Protocol: Switching to Dry Mode
Moisture Removal:
Drain wet cell completely
Remove wet cell components
Dry all surfaces thoroughly (minimum 20 minutes air dry or compressed air)
Inspect under lighting to confirm no residual moisture
Component Setup:
Install dry lens trays
Verify clean, dry optical surfaces
Software Configuration:
Select dry measurement mode
Confirm appropriate calibration profile loaded
Verification:
Measure dry reference lens three times
Confirm repeatability ≤0.03 D at 0.5% power accuracy
Document verification results
Contest MP High-Volume Protocol
The Contest MP system handles up to 50 dry lenses or 12 wet lenses per automated cycle with 4-second measurement time per lens. Switching protocols are similar to Contest 2 but emphasize automation:
For wet-to-dry switching: The automated tray system requires thorough drying of all lens-holding positions. Run an empty dry cycle after cleaning to verify no moisture contamination.
For dry-to-wet switching: Ensure saline reservoir is filled and temperature-stabilized. The system monitors solution temperature automatically; wait for temperature indicator to confirm 35°C before beginning measurements.
Medium Selection: Water, Saline, or Air
Rotlex IOLA systems support measurement in water, saline, or air. Selection depends on several factors:
Deionized Water
Advantages: Consistent optical properties, readily available, lower cost than saline
Considerations: Does not perfectly simulate the ionic environment of aqueous humor
Typical use: Standard production measurement, general quality control
Balanced Saline Solution (BSS)
Advantages: Better simulation of in-vivo conditions, appropriate ionic strength
Considerations: Higher cost, potential for crystallization if solution evaporates
Typical use: Clinical correlation studies, regulatory submissions requiring physiological conditions
Air (Dry Measurement)
Advantages: Fastest throughput (no solution preparation, no drying time), highest batch capacity (50 lenses vs 12)
Considerations: Only appropriate for hydrophobic materials that maintain optical properties when dry
Typical use: Hydrophobic acrylic IOL production, initial screening before final wet verification
Selection Decision Guide
For hydrophobic acrylic IOLs: Dry measurement is appropriate and offers 4x higher batch throughput (50 vs 12 lenses per cycle)
For hydrophilic acrylic IOLs: Wet measurement required; select water or saline based on regulatory requirements
For contact lenses: Contest systems support both modes; high-water-content lenses require hydrated measurement at 35°C to simulate on-eye conditions
Quality Control Considerations During Mode Switching
Cross-Contamination Prevention
The most common error when switching measurement modes is cross-contamination: moisture on dry components or contamination in wet solutions.
Prevention strategies:
Maintain separate, labeled storage for wet and dry components
Never mix wet and dry trays in the same storage area
Use dedicated cleaning supplies for each mode
Implement color-coded systems (e.g., blue labels for wet components, yellow for dry)
Calibration Verification After Switching
Always perform verification measurement with certified reference lenses after any mode switch, even if the switch takes only a few minutes. Verification confirms:
Correct calibration profile is loaded
No contamination is affecting measurements
System is operating within specification (0.04 D repeatability for IOLA, 0.03 D for Contest)
Documentation Requirements
Maintain records of every mode switch including:
Time and date of switch
Operator identification
Pre-switch verification results
Post-switch verification results
Any anomalies or corrective actions
This documentation supports ISO 13485 quality management system requirements and FDA 21 CFR Part 820 compliance for medical device manufacturing.
Troubleshooting Common Switching Issues
Issue: Repeatability Degradation After Switching to Wet Mode
Possible causes:
Air bubbles in optical path
Temperature instability in measurement solution
Contamination on wet cell surfaces
Corrective actions:
Inspect wet cell under angled lighting for bubbles; gently agitate to release
Verify solution temperature is stable (±2°C)
Clean and refill wet cell with fresh solution
Allow additional equilibration time (15-30 minutes)
Issue: Measurement Bias After Switching to Dry Mode
Possible causes:
Residual moisture on optical surfaces
Incorrect calibration profile loaded
Reference lens contamination
Corrective actions:
Re-clean and extend drying time
Verify software is configured for dry mode
Clean and re-measure reference lens
Issue: Verification Failure After Mode Switch
Possible causes:
Reference lens damage or contamination
Incomplete mode switching procedure
Environmental conditions outside specification
Corrective actions:
Inspect reference lens; clean or replace if necessary
Repeat full switching protocol from beginning
Verify temperature and humidity are within range
If verification continues to fail after these steps, contact Rotlex support. The company provides response within 24 hours and offers remote diagnostics capability.
Throughput Optimization Strategies
Minimizing Mode Switching Frequency
Each mode switch requires 30-45 minutes when including proper drying time and verification. Minimize switching by:
Batch scheduling: Group all wet measurements together, all dry measurements together
Dedicated systems: For high-volume facilities, dedicate separate IOLA systems to wet and dry measurement rather than switching a single system
Production planning: Schedule wet products on specific days, dry products on others
Parallel Processing
Facilities with multiple Rotlex systems can process wet and dry products simultaneously:
System A: IOLA MP configured for wet measurement (12 lenses per cycle)
System B: IOLA MP configured for dry measurement (50 lenses per cycle)
This configuration eliminates switching entirely while maintaining maximum throughput for both product types.
Time Budget for Mode Switching
Realistic time allocation for a complete mode switch:
Complete current batch and export data: 5-10 minutes
Remove current mode components: 5 minutes
Clean optical surfaces: 10 minutes
Drying time (wet to dry): 20-30 minutes
Install new mode components: 10 minutes
Software configuration: 5 minutes
Solution preparation (dry to wet): 10-15 minutes
Thermal equilibration: 15 minutes
Verification measurement: 10 minutes
Total switching time: 30-45 minutes (dry to wet) or 45-60 minutes (wet to dry)
System-Specific Technical Specifications Reference
IOLA 4C Specifications
Measurement time: 4 seconds per lens
Power range: -120 D to +160 D
Cylinder range: up to 30 D
Accuracy: 0.04 D (+0.25% for high powers)
Repeatability: 0.04 D
Lateral resolution: 8 µm
Model eyes: 4 interchangeable physical corneas
Measurement media: water, saline, or air
Data export: TXT, Excel, custom reports, API integration
Compliance: CFR 21 Part 11, ISO 11979-2
IOLA MP Specifications
Measurement time: 4 seconds per lens
Batch capacity: up to 50 dry lenses or 12 wet lenses per automated cycle
Power range: -125 D to +165 D
Cylinder range: up to 10 D
Accuracy: 1 D + 0.25% (up to 35 D)
Repeatability: 0.04 D
Operating temperature: 5°C to 45°C
Dimensions: 30 × 15 × 52 cm
Weight: 7.5 kg
Power: 12 V DC
Operating system: Windows 10/11
IOLA MFD Specifications
Measurement time: 9 seconds (19 seconds for toric lenses)
Wavelength: 545 nm
Accuracy: better than 0.25%
Lateral resolution: 25 µm
Power range: -20 D to +45 D
Features: through-focus MTF, through-frequency MTF, wavefront analysis, Zernike decomposition
Applications: multifocal, diffractive, toric IOL evaluation
Contest 2 and Contest MP Specifications
Measurement time: 3-4 seconds per lens
Power accuracy: 0.5% (approximately 0.03 D)
Repeatability: 0.03 D
Power range: -30 D to +30 D
Batch capacity (Contest MP): up to 50 dry or 12 wet lenses
Operating temperature: 5°C to 45°C
Hydrated measurement: 35°C temperature-stabilized saline
Dimensions (Contest MP): 54 × 28 × 54 cm
Weight (Contest MP): 10 kg
Supported lens types: disposables, spheric, aspheric, hydrogel, toric, progressive multifocal, RGP, scleral, Ortho-K, myopia-control
Regulatory and Quality System Alignment
ISO 11979-2 Compliance
Wet and dry measurement protocols must align with ISO 11979-2 requirements for IOL optical properties testing. IOLA systems incorporate ISO 11979-2 conversion algorithms that translate measurements taken under various conditions to standardized values.
When switching modes, verify that your selected model eye configuration and measurement medium match your regulatory submission requirements. Different regulatory bodies may specify different test conditions.
ISO 13485 Quality Management
Mode switching procedures should be documented within your ISO 13485 quality management system as controlled procedures. Required documentation includes:
Written switching procedures (this document can serve as a template)
Training records for personnel performing switches
Verification records for each switch
Deviation and corrective action procedures for failed verifications
FDA 21 CFR Part 820
For manufacturers subject to FDA regulations, mode switching falls under process control requirements (820.70) and equipment qualification requirements (820.72). Maintain records demonstrating that measurement equipment performs within specifications after each mode change.
IOLA and Contest systems support CFR 21 Part 11 compliant electronic records, providing audit trails, electronic signatures, and secure data management that satisfy FDA requirements.
Preventive Maintenance Considerations
Annual Calibration Verification
Rotlex recommends annual calibration verification under normal operating conditions. The motion-free optical metrology design used in IOLA and Contest systems provides exceptional calibration stability-months to years between calibrations under stable environmental conditions.
However, mode switching subjects components to additional handling. Facilities with frequent wet/dry switching should consider:
More frequent calibration verification (quarterly rather than annual)
Dedicated wet and dry components to reduce handling wear
Regular inspection of frequently-handled items (wet cells, lens holders, physical corneas)
Component Replacement Schedule
Track usage cycles for components subject to wear:
Wet cells: inspect for scratches, cloudiness, or seal degradation every 1,000 wet cycles
Physical corneas (IOLA 4C): inspect optical surfaces every 500 cycles; handle with extreme care
Lens holders and trays: inspect for wear or damage every 5,000 cycles
Replace components showing any visible degradation. A scratched wet cell will affect every subsequent measurement until replaced.
Implementation Checklist
Use this checklist when implementing wet/dry switching protocols in your facility:
Documentation and Training
Written switching procedures approved and version-controlled
Personnel trained on both wet and dry protocols
Training records documented
Verification forms and logs prepared
Equipment and Supplies
Wet cells appropriate for lens types measured
Fresh saline or deionized water supply established
Reference lenses certified for both wet and dry measurement
Cleaning supplies dedicated to each mode
Proper storage locations designated for wet and dry components
Quality System Integration
Switching procedures integrated into quality management system
Calibration and verification requirements documented
Deviation and corrective action procedures established
Records retention procedures confirmed
Production Planning
Batch scheduling minimizes unnecessary mode switches
Switching time budgeted into production schedules
Throughput impact understood and communicated to planning teams
Conclusion
Switching between wet and dry measurement modes on Rotlex IOLA and Contest systems is a routine but critical procedure that directly impacts measurement accuracy and production efficiency. By following systematic protocols-including proper component handling, thorough cleaning and drying, software configuration, and verification measurement-manufacturers maintain the 0.04 D repeatability (IOLA) and 0.03 D repeatability (Contest) that these systems deliver.
The key principles for successful mode switching are: complete preparation before switching, thorough cleaning and drying during transition, verification measurement after switching, and comprehensive documentation throughout. These practices support both measurement accuracy and regulatory compliance for ISO 13485, FDA 21 CFR Part 820, and ISO 11979-2 requirements.
For facilities with high wet and dry volumes, consider dedicating separate systems to each mode to eliminate switching entirely. The IOLA MP’s 50-lens dry capacity and 12-lens wet capacity enable high throughput in both configurations without compromise.
Disclaimer: This document is intended for educational and operational guidance. It does not replace official Rotlex documentation or training. For specific regulatory requirements, consult with your quality assurance team and relevant regulatory authorities.
