Intraocular Lens Characterization

Biomaterials Mechanical Testing IOL Design Force-Displacement Data Analysis Compression Testing Incision Size Optimization

Overview

Which Material Allows the Smallest Incision?

Intraocular lenses (IOLs) are implanted to replace the eye's natural lens during cataract surgery — one of the most common surgical procedures globally. A key design requirement is the ability to fold the lens for insertion through the smallest possible incision, reducing surgical trauma and recovery time.

This research project tested three IOL materials — hydrophobic acrylic, hydrophilic acrylic, and PMMA — to determine which allows the smallest incision size for safe lens insertion.

PMMA

Peak force: ~27 N

Highest compressive forces, least flexible — requires the largest incision. The original rigid IOL material.

Hydrophobic Acrylic

Best performer

Enables 2+ mm reduction in incision size. Foldable, low water uptake. Optimal material per study findings.

Hydrophilic Acrylic

1.5 mm reduction

Slightly lower performance than hydrophobic. Higher water content, unique wrinkling behavior under compression.

Methodology & Key Outcomes

Built a custom compression rig from popsicle sticks and elastic bands to apply controlled displacement
Compressed each lens sample to half its diameter (2.5 mm) — simulating insertion through an injector
Collected force-displacement data during both loading and unloading phases across multiple trials
Filmed each test from the side view to analyze bending angles and deformation geometry
Averaged data across trials and compared stiffness and failure behaviour per material
PMMA exhibited ~27 N peak force with brittle-like behaviour — confirming it requires the largest incision
Hydrophobic acrylic demonstrated the best flexibility — enabling 2+ mm incision size reduction
Hydrophilic acrylic showed a unique wrinkling behaviour and ~1.5 mm incision reduction

"Hydrophobic acrylic is the optimal material for reducing incision size, though clinical considerations such as cost, surgeon experience, and biocompatibility must also be factored in when selecting an IOL material for a specific patient."

Technical Approach

Controlled Compression & Video Analysis

The custom compression rig constrained the lens laterally while a known displacement was applied vertically — replicating the geometry of folding a lens through an injector nozzle. Elastic bands provided a calibrated force that increased with displacement, while the popsicle stick frame maintained consistent alignment across trials.

Side-view filming captured the actual bending profile of each lens material at equivalent displacement levels. Bending angle measurements from the footage were correlated with force readings to build a more complete picture of material compliance — going beyond a simple force-displacement number to understand the spatial deformation each material undergoes during real surgical insertion.