Introduction

Correction of moderate-to-high myopia remains a significant challenge in refractive surgery, particularly in patients unsuitable for corneal refractive procedures such as LASIK or PRK. Implantable Collamer Lens (ICL) implantation has emerged as an effective alternative because of its reversibility, excellent optical quality, and preservation of corneal tissue.

The EVO ICL developed by STAAR Surgical has demonstrated excellent refractive outcomes and safety profiles in properly selected patients. Appropriate patient selection is essential to minimize complications such as cataract formation, angle crowding, pigment dispersion, and glaucoma. One of the critical anatomical parameters for EVO ICL candidacy is anterior chamber depth (ACD). Current manufacturer recommendations suggest a minimum ACD of 2.8 mm (internal) for myopic correction.

Patients with low ACD are generally excluded from ICL implantation due to concerns regarding insufficient postoperative vault and potential contact between the crystalline lens and the implanted lens. Nevertheless, some patients with severe refractive errors and contraindications to corneal laser correction may still benefit from carefully planned off-label implantation.

In this report, we present two patients with ACD measurements below the recommended threshold who underwent successful bilateral EVO ICL implantation with favorable short-term postoperative outcomes.

Recent advances in posterior chamber phakic intraocular lens technology, particularly the introduction of the central port design in EVO ICL, have improved aqueous humor circulation and reduced the incidence of complications such as anterior subcapsular cataract formation. Despite these improvements, anterior chamber depth remains a critical parameter in patient selection because inadequate space between the implanted lens and crystalline lens may increase the risk of long-term complications. Consequently, implantation in eyes with shallow anterior chambers continues to be considered relatively contraindicated, and evidence regarding outcomes in such borderline anatomical cases remains limited.

Case Presentation

Two patients with high myopia who were unsuitable candidates for corneal refractive surgery underwent off-label bilateral EVO Implantable Collamer Lens (ICL) implantation despite having anterior chamber depth (ACD) measurements below the minimum recommended threshold proposed by STAAR Surgical. The first patient was a 39-year-old male with high myopic astigmatism, while the second patient was a 31-year-old female with severe bilateral myopia. Both patients presented with significant dependence on spectacles and sought refractive surgical correction to improve visual quality and achieve spectacle independence. Comprehensive ophthalmic assessment including manifest refraction, corneal tomography, pachymetry, anterior segment imaging, ultrasound biomicroscopy (UBM), Pentacam analysis, and IOLMaster measurements was performed in all eyes.  External ACD values measured by IOLMaster is 3 mm, internal ACD values measured by Pentacam and UBM ranged between 2.54 mm and 2.71 mm, which are below the recommended safety threshold for standard EVO ICL implantation. Because corneal laser refractive procedures were considered unsuitable due to the degree of refractive error and anatomical limitations, posterior chamber phakic IOL implantation was considered after extensive counseling regarding the off-label nature of the procedure and its potential risks, including insufficient vault, anterior subcapsular cataract formation, angle crowding, pigment dispersion, and elevated intraocular pressure. Bilateral EVO ICL implantation was successfully performed in both patients using 12.1 mm lenses with individualized refractive power selection. Postoperative follow-up included serial anterior segment optical coherence tomography (AS-OCT) evaluation to assess lens position and vault measurements. In all implanted eyes, postoperative vault remained within clinically acceptable ranges during day 1, day 7, and day 30 follow-up examinations, with measurements ranging from 210 µm to 399 µm. Both patients demonstrated satisfactory visual rehabilitation, stable lens positioning, clear crystalline lenses, and absence of significant postoperative complications such as cataract formation, abnormal vaulting, angle closure, or elevated intraocular pressure during the early postoperative period. These cases demonstrate that carefully selected patients with borderline low ACD may achieve favorable short-term outcomes following off-label EVO ICL implantation when detailed biometric evaluation and close postoperative monitoring are performed.

All procedures were performed under sterile operating room conditions by an experienced refractive surgeon. Standard EVO ICL implantation technique was used. After creation of a temporal clear corneal incision, viscoelastic material was injected into the anterior chamber followed by insertion of the foldable EVO ICL into the posterior chamber. The haptics were carefully positioned behind the iris, and complete viscoelastic removal was performed at the conclusion of surgery. Postoperative treatment included topical antibiotics and corticosteroids.

Case 1

A 39-year-old male presented to the refractive surgery clinic with progressive difficulty in distance vision affecting both occupational and daily visual activities. The patient had a long-standing history of high myopia with significant astigmatism and was dependent on spectacles for visual function. He expressed dissatisfaction with the quality of vision obtained with spectacles because of image minification and distortion associated with high refractive correction. The patient was interested in refractive surgical correction to achieve spectacle independence.

Comprehensive ophthalmic evaluation was performed. Manifest refraction demonstrated high bilateral myopic astigmatism. Best corrected visual acuity (BCVA) was 0.8 in the right eye and 0.9 in the left eye.

Preoperative Refraction

Slit-lamp examination showed clear corneas, deep peripheral chambers clinically, and transparent crystalline lenses bilaterally. Intraocular pressure was within normal limits in both eyes. Fundus examination revealed myopic retinal changes without retinal tears or degenerative lesions requiring treatment.

Corneal laser refractive surgery was considered unsuitable because of the degree of refractive error and anatomical considerations. Therefore, phakic intraocular lens implantation was evaluated as an alternative refractive solution.

Detailed anterior segment biometric analysis was performed using multiple imaging modalities including IOLMaster 700, Pentacam, and ultrasound biomicroscopy (UBM). Although external ACD measurements obtained by IOLMaster were above 3 mm, internal ACD measurements obtained through Pentacam and UBM demonstrated values below the manufacturer-recommended safety threshold for EVO ICL implantation. External ACD from measurement from IOL master 700 must be reduces by central corneal thickness (CCT) to obtain internal ACD. In this case 3.21mm-530 micrometer = 2.68mm right eye and 3.19mm-531 micrometer=2.65mm for left eye.

Anterior Segment Measurements

The patient was extensively counseled regarding the off-label nature of the procedure, possible anatomical risks associated with reduced anterior chamber depth, and the importance of close postoperative follow-up. After detailed informed consent, bilateral EVO ICL implantation was planned.