An Implantable Collamer Lens (ICL) is a type of posterior chamber phakic intraocular lens (pIOL). It corrects refractive errors by inserting a lens between the iris and the natural lens (ciliary sulcus) while preserving the natural lens.
The implantable collamer lens is made of a patented material called “collamer” developed by STAAR Surgical. Its composition is as follows:
This material has excellent permeability to gases and nutrients, and causes very little inflammatory reaction 1).
In 1993, STAAR Surgical launched the first posterior chamber phakic IOL. It received FDA approval in the United States in 2005, and after several design changes, the EVO/EVO+ phakic posterior chamber lens was FDA-approved in the US in March 2022. Over 2 million lenses have been used worldwide, of which more than 1.5 million are the central-port design EVO model 1).
The latest EVO phakic posterior chamber lens features a central port (KS-Aquaport) with a diameter of 0.36 mm. This design provides the following advantages:
LASIK corrects refraction by ablating the cornea with a laser. A phakic posterior chamber lens preserves the cornea and inserts a lens inside the eye. The phakic posterior chamber lens is reversible and carries no risk of dry eye or corneal ectasia. It also does not affect IOL power calculation for future cataract surgery 1). For high myopia, the phakic posterior chamber lens is considered advantageous.
The following are the 6-month results from the US FDA clinical trial for the moderate myopia group (200 eyes) 1).
The results for corrected distance visual acuity (CDVA) are as follows1).
Comparison results with corneal refractive surgeries such as LASIK are shown below1).
| Procedure | UDVA 20/20 or better | Within ±0.50 D |
|---|---|---|
| EVO phakic posterior chamber lens | 94.5% | 91.5% |
| SMILE | 84.2% | 93.7% |
| Topo-LASIK | 88.9% | 93.0% |
The EVO implantable collamer lens (ICL) shows efficacy and safety equivalent to or better than corneal refractive surgery1).
Based on US FDA approval, the indications for the Visian ICL are as follows:
Accurate determination of lens size directly affects postoperative outcomes. Measurement is performed using the following methods.
The ideal vault (gap between ICL and anterior lens surface) is 250–750 μm2). Too low vault increases risk of anterior subcapsular cataract; too high vault may cause pupillary block or angle narrowing.
If vault is less than 250 μm, there is a risk of anterior subcapsular cataract formation due to contact with the crystalline lens. If vault exceeds 750 μm, pupillary block or pigment dispersion from iris contact may occur2). In FDA trials, 0.5% of eyes required lens exchange due to excessive vault1).
With conventional Visian phakic posterior chamber lenses, YAG laser iridotomy was performed at two superior sites 2–3 weeks before surgery. With EVO/EVO+ phakic posterior chamber lenses, peripheral iridotomy is not required1).
The EVO phakic posterior chamber lens has demonstrated high safety, but some complications have been reported.
Elevated Intraocular Pressure
OVD retention: Most common. Transient elevation in 18% within 1–6 hours postoperatively 1).
Steroid response: Occurs in 0.5%. Managed by steroid tapering 1).
Angle narrowing: Due to excessive vaulting. May require lens exchange 1).
Infection/Inflammation
TASS: Incidence 0.24%. May develop late around 1 week postoperatively. Improves with intensive steroid therapy 3).
Endophthalmitis: Incidence 0.017–0.036%. Visual recovery possible with appropriate antibiotic treatment 4).
Other
Hyphema: Occurs due to rupture of iridociliary cysts. May heal with conservative treatment 5).
Cataract formation: Incidence of visually significant cataract is 0% with EVO phakic IOL 1).
Early postoperative IOP elevation may have multiple causes 2).
In a case reported by Moshirfar et al. (2024), postoperative IOP elevation was presumed to be caused by retained viscoelastic material and early steroid response 2). With 6 weeks of observation and steroid tapering, it normalized without requiring lens explantation or iridotomy.
The mean corneal endothelial cell loss rate at 6 months was 2.2% 1). Long-term studies show stabilization after early postoperative remodeling, with a loss rate of 3.6 ± 7.9% at 8 years 1).
Li et al. (2023) reported two cases of delayed TASS occurring 1 week after phakic posterior chamber IOL surgery 3). Keratic precipitates (KP) on the posterior cornea and fibrin formation in the anterior chamber were observed, but with systemic and topical steroid therapy (prednisolone 0.5 mg/kg orally + 1% eye drops every hour) for 4–5 weeks, both visual acuity and anterior chamber findings improved. The incidence rate was 0.24% (2 out of 827 eyes).
Zheng et al. (2023) reported a case of Staphylococcus epidermidis endophthalmitis occurring 20 days after phakic posterior chamber IOL surgery 4). Intravitreal injections (vancomycin 1 mg + ceftazidime 2 mg) were administered twice, and visual acuity recovered to 22/20 without explantation of the phakic IOL or vitrectomy. The incidence of endophthalmitis after phakic posterior chamber IOL surgery is estimated to be approximately 0.017–0.036%.
The most common cause is retained viscoelastic material, which usually resolves spontaneously within a few days. Management includes reducing steroid eye drops or adding IOP-lowering medications. If caused by pupillary block or lens size mismatch, iridotomy or lens exchange may be necessary 2).
Collamer has extremely high biocompatibility. Examinations using specular microscopy and laser flare cell meter have confirmed the absence of inflammatory reaction 1). Its collagen content provides high affinity with biological tissues and excellent permeability to gases and metabolites.
The optic of the phakic posterior chamber IOL is positioned in an arching manner above the crystalline lens. Proper maintenance of the vault between the IOL and the lens allows aqueous humor to flow over the lens surface, preventing cataract formation.
The central port (KS-Aquaport) of the EVO implantable collamer lens allows physiological aqueous humor flow from the posterior chamber to the anterior chamber. This provides the following effects:
In the FDA study, 99.7% of eyes achieved satisfactory vault, and there were zero cases of angle closure, pigment dispersion, or anterior subcapsular cataract1).
This is an innovative implantable collamer lens that received CE mark approval in July 2020. It features an aspheric extended depth of focus (EDOF) optics and provides correction for near and intermediate vision. It is indicated for both phakic and pseudophakic eyes (eyes with monofocal IOL after cataract surgery), with an age range of 21 to 60 years. It is awaiting FDA approval in the United States.
Traditionally, phakic posterior chamber lenses were mainly indicated for high myopia of -6.0 D or more, but with the improved safety of the EVO phakic posterior chamber lens, the indication is expanding to moderate to low myopia.
In the FDA clinical trial by Packer (2022), about one-third of the subjects had moderate myopia of less than -6.0 D, and safety and efficacy were shown to be consistent across the full range of myopia 1).
A phakic posterior chamber lens for presbyopia correction called EVO Viva has been developed and has received CE mark approval in Europe. It is designed to improve near and intermediate vision with an extended depth of focus optical system, but it is still awaiting FDA approval in the United States.
