Implantable Collamer Lens
Posterior Chamber Phakic Intraocular lenses
Implantable collamer lenses are a type of posterior chamber phakic intraocular lens (pIOL). pIOL are usually used for high degrees of refractive error or when corneal refractive surgery is contraindicated. Advantages over corneal refractive surgery also include quicker recovery and reversibility. Posterior chamber pIOL provide a more cosmetically appealing alternative to anterior chamber (AC) pIOL because they are less visible externally and create less risk of endothelial cell loss (ECL) as they are placed further away from the cornea.  They are a safer alternative to refractive less exchange which carries a risk of retinal detachment and loss of accommodation.  There have been a number of posterior chamber phakic intraocular lenses on the market prior to the development of the implantable collamer lens. These include the Chiron Adatomed pIOL which was a rectangular, silicone plate IOL that was eventually discontinued because of high rates of AC inflammation and cataracts.  The PRL Phakic Refractive Lens (CIBA Vision) was another 1-piece pIOL made of hydrophobic silicone elastomer designed so the haptics would rest on the zonules and the lens would float above the natural crystalline lens; however this lens was taken off of the market due to high incidence of subluxation of the lens into the vitreous cavity secondary to zonular dehiscence.  Currently there is only one FDA approved posterior chamber pIOL in the US which is the implantable collamer lens (ICL).
Implantable Collamer Lens
In 1993, STAAR Surgical (Monrovia, CA, USA) released their posterior chamber pIOL. The company created a biocompatible material called collamer which is a blend of polymer and collagen with the purpose of making the lens lighter, hydrophilic, and allowing for better exchange of gas and nutrients.  This patented material is made of 60% poly-hydroxymethylmethacrylate (HEMA), water (36%), and benzophenone (3.8%) and 0.2% porcine collagen. 
The lens underwent a number of design modification and was FDA approved in 2005. The current model available in the US is the Visian ICL V4, and it has been commercially available since 2011 to correct myopia. The toric version was FDA approved in 2018 to correct or reduce myopia with astigmatism. The ICL is a rectangular one-piece plate-haptic design lens that is plano-concave. Both lenses are available in four lengths (12.1, 12.6, 13.2, and 13.7 mm) and is 7.5 -8.0 mm wide.3,4 The V4c or EVO model, a more recent model not yet available in the U.S., features a central port or hole of 0.36 mm (KS-Aquaport) meant to eliminate the need for Nd:YAG iridotomy or iridectomy that was required in patients who had the previous model Visian V4 implanted.   The port is meant to allow physiologic aqueous humor circulation. The lens also has a ultra-violet absorbing chromophore.The EVO/EVO+ ICL Model V5 is the latest ICL released. It has a larger optic diameter up to 6.10 and can be used to correct residual refractive error after cataract surgery as well as a novel 360 micron port in the center of the optic. This port allow for aqueous flow through the lens, which eliminates the need for the surgeon to perform peripheral iridotomies prior to ICL surgery.   The EVO/EVO+ ICL and its Toric version were both FDA approved in the United States in March 2022. There is also safety data showing that the central port allowing for physiologic flow through the optic reduces the rate of anterior subcapsular cataract formation and pupillary block compared to earlier models.
As approved by the US FDA, the Visian ICL is indicated for adults 21-45 years of age
- To correct myopia ranging from -3.0 diopters to -15.0 diopters with less than or equal to 2.5 diopters of astigmatism at the spectacle plane
- To reduce myopia ranging from greater than -15.0 diopters to -20.0 diopters with less than or equal to 2.5 diopters of astigmatism at the spectacle plane
- Anterior chamber depth (ACD) 3.00 mm or greater is required for implantation.
- Stable refractive history within 0.5 diopter for 1 year is required prior to implantation.
The Visian Toric ICL is indicated for use in patients 21-45 years of age
- For the correction of myopic astigmatism with spherical equivalent ranging from -3.0D to ≤-15.0D (in the spectacle plane) with cylinder (spectacle plane) of 1.0D to 4.0D.
- For the reduction of myopic astigmatism with spherical equivalent ranging from greater than -15.0D to -20.0D (in the spectacle plane) with cylinder (spectacle plane)1.0D to 4.0D.
- With an anterior chamber depth of 3.00 mm or greater, when measured from the corneal endothelium to the anterior surface of the crystalline lens
- A stable refractive history (within 0.5D for both spherical equivalent and cylinder for 1 year prior to implantation)
- The Visian TICL is intended for placement in the posterior chamber (ciliary sulcus) of the phakic eye.
- Anterior chamber depth from endothelium < 3.00 mm
- Anterior chamber angle less than grade II determined by gonioscopic examination
- Pregnancy or nursing
- Not meeting appropriate endothelial cell density as determined by an age-dependent minimum (range 1900- 3875 cells/mm2), see Table 1
Prior to surgery, all patients require a complete ophthalmologic examination including uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), vertex distance, manifest and cycloplegic refraction, white to white measurement, slit-lamp biomicroscopy, intraocular pressure measurement via Goldmann applanation tonometry, corneal evaluation including central corneal thickness measurement, endothelial cell count, as well as anterior chamber depth. Furthermore patients should undergo dilated retinal examination and evaluation for the presence of retinal tears or lesions.
Nomograms are available from STAAR Surgical to select the correct pIOL size based on white to white measurement and anterior chamber depth measured from the corneal endothelium to the crystalline lens (ACD-pachymetry). The method used for ICL sizing in the FDA study is external white-to-white horizontal distance (with calipers) and anterior chamber depth by Scheimpflug photography.  Another modality available to measure white to white is the Visante anterior segment OCT. Recently ultrasound biomicroscopy has been used to measure sulcus-to-sulcus distance instead of white to white. It can also measure the rise of the anterior capsule which can influence the size of the lens.  Accurate sizing of the lens is important as it affects the vault of the ICL. The optics of the ICL are placed in a manner to preserve a space between the crystalline lens and the ICL. It is “vaulted” over the crystalline lens. This space allows for aqueous flow over the crystalline lens, which is thought to prevent cataract formation. Ideally the size of the vault should be approximately 250-750 microns (0.5- 1.5 xcorneal thickness). A larger lens is associated with higher vault. If a vault is less than 250 microns, there is risk anterior subcapsular cataract formation. A vault greater than 750 microns risks pupillary block glaucoma and crowding of the angle with possible iris chafing and resultant loss of pigment. 
IOL power calculation
ICL power calculation is performed through the online calculator provided by the modified vertex formula provided by STAAR surgical. The power calculation is based on several variables in the formula including preoperative manifest spherical and cycloplegic refractive error, keratometric power, corneal thickness, horizontal visible iris dimension (HVID) and central ACD.  ACD is measured from the corneal epithelium to the crystalline lens, as opposed to lens size calculation where the ACD is measured from the back of the cornea thus subtracting corneal thickness. Careful patient testing and measurement are essential and recommended.
For the Visian ICL models available currently in the US, two YAG iridotomies placed superiorly 90 degrees apart, should be performed 2 to 3 weeks prior to surgery with confirmation of the patency of the iridotomies prior to lens implantation. Alternatively, iridotomies can be performed at the time of surgery. With the EVO/EVO+ ICL and toric version peripheral iridotomies are no longer necessary.
Visian and EVO Visian ICL implantation can be performed under topical anesthesia supplemented with intracameral lidocaine or peribulbar anesthesia. The pupil is dilated preoperatively. Tropicamide 1% and phenylephrine 2.5% are preferred dilating agents; the use of longer acting agents may make it difficult to constrict the pupil at the end of the procedure. A clear temporal corneal incision measuring 3.0 to 3.2mm is made and two paracenteses incisions are made superiorly and inferiorly. Cohesive viscoelastic (Occucoat, Bausch and Lomb) is used to fill the anterior chamber before insertion of the ICL and after the lens unfolds inside the eye. Occucoat is recommended since other viscoelastic agents may be catarogenic when trapped between the ICL and the crystalline lens. It is important not to overfill the anterior chamber as it would make it harder to tuck the haptics. The ICL is injected anterior and parallel to the iris plane into the anterior chamber, and allowed to naturally unfold. More viscoelatic is injected anterior to the lens. The haptics footplates are then positioned under the iris. A Batlle manipulator aids in tucking the haptics of the ICL under the iris. Generally, the distal haptics (away from the incision) are positioned prior to the proximal haptics. Avoidance of contact with the central 6.0 mm of the ICL is recommended to avoid lens damage. The surgeon should avoid touching the crystalline lens and cornea (no fly zone) during the procedure to minimize risk of cataract formation and intraoperative complications. Throughout the procedure positioning instruments are used through the paracentesis ports and should be kept peripheral with minimal central touch. Viscoelastic should be removed completely after conclusion of the case in order to reduce risk of Intraocular pressure (IOP) spike postoperatively. A miotic agent such as Miostat or Miochol (pilocarpine) is instilled prior to ensuring a water tight incision. The lens vault and IOP should be checked within a few hours after the procedure and the next day. The lens vault should be estimated by slit lamp biomicroscopy and should be around (1.0 +- 0.5) * corneal thickness. Patency of the iridotomy sites must be confirmed with the Visian ICL, no the EVO. Postoperatively, patients should be prescribed antibiotic eye drops for 1 week and topical steroid eye drops with tapering for approximately 2 to 4 weeks. In the United States, it is common and accepted practice to perform same day bilateral sequential surgery. Otherwise, the procedure can be repeated on the second eye within 1 or 2 weeks.
Visian ICL Implantation Video:
Visian Toric ICL Implantation Video:
EVO Visian ICL Implantation Video:
In the US FDA 3-year follow up study evaluating the ICL, for patients with BSCVA of 20/20 or better at baseline, 98.4% of patients ≤ 7-D and 86.9% of patients ⬎7- to 10-D, and reported 20/20 or better uncorrected vision. For highly myopic patients (> -10D), 83.8% reported UCVA of 20/40 or better 3 years post-op.  Furthermore, studies comparing laser in situ keratomileusis (LASIK) to ICL implantation have found ICL to be superior in treating patients with higher degrees of myopia.
Quality of Vision and Quality of Life Outcomes
ICL seem to induce significantly fewer ocular higher-order aberrations (HOAs) than wave front-guided LASIK and better contrast sensitivity.  In studies comparing ICL versus LASIK, patients with ICL reported better vision–related quality of life including less activity limitations, fewer symptoms such as eye dryness or discomfort, and better appearance compared with patients who had undergone LASIK. 
The FDA clinical trial of the Visian ICL found that patients with a higher degree of pre-operative myopia had a higher rate of complications. all of the patients that lost 2 lines of best-spectacle-corrected visual acuity (BSCVA) occurred in patients in the > -10D group.  Furthermore all of the patients requiring cataract extraction, as well as those requiring secondary surgery to reposition the ICL occurred in the > -10D myopia group. In the study, 5 eyes (1%), lost greater than 2 lines of BSCVA, with 3 of occurring secondary to nuclear opacities that developed between 1 and 3 years postop. The rate of clinically significant cataract formation amongst all the groups was 0.4% for anterior subcapsular opacities and 1% of nuclear opacities. With the new EVO/EVO+ ICL the rate of visually significant cataract has been cited at zero and the incidence of non visually significant Anterior Subcapsular Opacities (ASC) has remained very low.
Rarer complications necessitating secondary surgical intervention that have been reported include rotation of a toric lens, pupillary block, retinal detachment or elevated IOP.   Additional risk of complications can be attributed to the location of ICL between the iris and crystalline lens which can lead to contact with surface of the ICL and theoretically lead to pigment dispersion and/ or inflammation and possible secondary glaucoma.
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