Which of the following IOL materials has the highest refractive index and therefore allows the thinnest lens design?

Explanation

## IOL Materials and Refractive Index **Key Point:** Among commonly used IOL materials, **hydrophobic acrylic** has the highest refractive index (~1.55 for some formulations, typically cited as ~1.47–1.55), which allows the thinnest lens design for a given optical power. This is a fundamental principle: higher refractive index → thinner optic → smaller incision size. **High-Yield:** The relationship between refractive index and lens thickness is inverse — a higher refractive index permits thinner optics for the same optical power, reducing lens volume and improving foldability and wound closure ease. ### Comparison of Common IOL Materials | Material | Refractive Index | Foldability | Notes | |----------|------------------|-------------|-------| | PMMA | 1.49 | Non-foldable | Rigid; historically used, now rare | | Silicone | 1.41–1.46 | Foldable | Older foldable material | | Acrylic (hydrophobic) | 1.47–1.55 | Foldable | Highest RI among modern IOLs; thinnest design | | Collamer | ~1.45 | Foldable | Hydrophilic copolymer; used in phakic IOLs | **Why not PMMA?** Although PMMA has a refractive index of ~1.49, it is a rigid material that cannot be folded through small incisions, making it unsuitable for modern small-incision cataract surgery. Its high RI is therefore not clinically leveraged for thin-lens design in contemporary practice. **Why not Collamer?** Collamer (a hydrophilic acrylic–collagen copolymer) has a refractive index of approximately 1.45, which is lower than hydrophobic acrylic. It is primarily used in phakic IOLs (e.g., Visian ICL) rather than standard pseudophakic IOLs. **Why not Silicone?** Silicone has a refractive index of 1.41–1.46, lower than hydrophobic acrylic, and is associated with silicone oil droplet adherence in patients who may need vitreoretinal surgery. **Clinical Pearl:** Hydrophobic acrylic IOLs (e.g., AcrySof by Alcon) dominate modern cataract surgery because of their high refractive index enabling thin, foldable optics, excellent biocompatibility, and low posterior capsule opacification rates. *(Reference: Yanoff & Duker, Ophthalmology, 5th ed.; Kanski's Clinical Ophthalmology)*