Implantable Lenses and Phakic IOLs

The FDA has approved exactly two phakic intraocular lens (IOL) models for use in the United States — the Visian ICL (Implantable Collamer Lens) and the Verisyse lens — yet the global market for these devices continues to expand as refractive surgeons encounter patients whose corneas are too thin, too steep, or too irregular for LASIK. Phakic IOLs occupy a specific and important niche: correcting high refractive errors while leaving the eye's natural crystalline lens untouched.

What Makes a Lens "Phakic"?

The term "phakic" simply means the natural lens remains in the eye. This distinguishes phakic IOLs from the intraocular lenses placed during cataract surgery, where the natural lens is removed first. A phakic IOL is an additional lens, surgically inserted either in front of or behind the iris, that works alongside the eye's existing optics. Think of it as a permanent contact lens that lives inside the eye rather than on its surface.

Standard laser refractive procedures like LASIK reshape the cornea by removing tissue — a process that becomes problematic when the refractive error is large (typically beyond −8.00 diopters of myopia) or corneal thickness falls below roughly 500 micrometers. Phakic IOLs sidestep corneal tissue removal entirely, which is the core reason they exist.

Types of Phakic IOLs

Three anatomical positions define the main categories:

Anterior Chamber Angle-Supported Lenses

These lenses sit in the anterior chamber, with their supporting structures (haptics) resting in the drainage angle where the iris meets the cornea. Earlier generations caused endothelial cell loss and secondary glaucoma at rates that led to withdrawal of models like the NuVita MA20. The design approach has largely fallen out of favor.

Anterior Chamber Iris-Fixated Lenses

The Verisyse (known as Artisan outside the United States) clips onto the mid-peripheral iris using a technique called enclavation. The FDA approved the Verisyse in 2004 for myopia between −5.00 and −20.00 diopters (FDA Verisyse PMA). Because the lens sits in front of the iris, ongoing monitoring of corneal endothelial cell density is essential — cell counts that drop below approximately 1,500 cells/mm² raise concern for corneal decompensation.

Posterior Chamber Phakic Lenses

The Visian ICL, manufactured by STAAR Surgical, is placed behind the iris and in front of the natural lens in the ciliary sulcus. The FDA approved the Visian ICL (model V4) in 2005 for myopia ranging from −3.00 to −15.00 diopters (FDA Visian ICL PMA). The newer EVO model (V4c) incorporates a central port — a 360-micrometer hole — that allows aqueous humor to flow through the lens, eliminating the need for a pre-operative peripheral iridotomy in most cases. The toric variant of the EVO ICL received FDA approval in 2018 for combined correction of myopia and astigmatism up to 4.00 diopters (FDA EVO Toric ICL).

Posterior chamber phakic lenses have become the dominant category worldwide, largely because the ICL's position behind the iris reduces endothelial cell contact.

Outcomes and What the Data Show

The FDA clinical trial data for the Visian ICL reported that 94.7% of eyes achieved uncorrected visual acuity of 20/40 or better, with 59.3% reaching 20/20 or better (FDA Summary of Safety and Effectiveness). A 2023 meta-analysis published in the Journal of Cataract & Refractive Surgery covering over 4,000 eyes found that the EVO ICL achieved a mean postoperative spherical equivalent within ±0.50 diopters of target in approximately 85% of cases.

One persistent concern with posterior chamber phakic IOLs is cataract formation. The original Visian ICL (without the central port) showed anterior subcapsular cataract rates ranging from 1% to 10% depending on study duration and vault adequacy — vault being the critical distance between the back surface of the IOL and the front surface of the crystalline lens, ideally measured between 250 and 750 micrometers by anterior segment optical coherence tomography.

Key Risks and Monitoring Requirements

• Endothelial cell loss: Annual specular microscopy is recommended, particularly for iris-fixated lenses. The American Academy of Ophthalmology notes that progressive endothelial loss may necessitate lens explantation (AAO EyeWiki — Phakic IOLs).
• Elevated intraocular pressure: Pupillary block was a meaningful risk with pre-port ICL designs; the central port in the EVO model has substantially reduced this complication.
• Cataract development: Insufficient vault accelerates lens-to-lens contact and opacification. Sizing relies on white-to-white measurements and sulcus-to-sulcus dimensions, increasingly obtained via ultrasound biomicroscopy.
• Rotation (toric models): Toric ICL rotation beyond 30 degrees may require surgical repositioning.

Who Is a Candidate?

General candidacy parameters include age between 21 and 45, stable refraction for at least one year, adequate anterior chamber depth (≥2.8 mm for posterior chamber models), and endothelial cell counts above 2,000 cells/mm² (higher thresholds for younger patients). Patients with a history of iritis, glaucoma, or significant cataract are typically excluded.

How Phakic IOLs Fit Alongside Other Options

For moderate myopia (−1.00 to −8.00 diopters) with adequate corneal thickness, LASIK and PRK remain the most common procedures. Phakic IOLs become the preferred refractive option when corneal parameters are unfavorable or when the refractive error exceeds the safe treatment range for excimer laser ablation. In patients over 50 with early lens changes, refractive lens exchange — removing the natural lens and replacing it with a premium IOL — may be more appropriate than inserting a phakic lens that will eventually need to be removed at the time of cataract surgery anyway. The decision involves a careful balance between preserving accommodation (a meaningful advantage in patients under 40) and the long-term certainty that a cataract will eventually develop.

References

• FDA PMA Database — Verisyse Phakic IOL (P030028)
• FDA PMA Database — Visian ICL (P030016)
• FDA Summary of Safety and Effectiveness — Visian ICL
• FDA PMA Supplement — EVO Visian Toric ICL (P030016/S035)
• AAO EyeWiki — Phakic Intraocular Lenses

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