Patients who were evaluated from April 2017 to October 2019 for ICL implantation at Cleveland Clinic Abu Dhabi (CCAD) were included in this retrospective review. All patients underwent preoperative screening and examination, which included: uncorrected distance visual acuity (UDVA), best corrected distance visual acuity (BCVA), intraocular pressure (IOP) measurement, manifest spherical equivalent refraction (MRSE), slit lamp examination, gonioscopy, endothelial cell density (ECD) (CEM-530 Specular Microscopy, Nidek, Gamagori, Japan), corneal tomography (Galilei dual Scheimpflug system, Ziemer Ophthalmic System AG, Port, Switzerland), ocular biometry (IOL Master, Carl Zeiss Meditec AG, Jena, Germany), manual horizontal corneal diameter white-to-white measurement, cycloplegic refraction and dilated fundus examination.

Qualitative UBM analysis was done with the 50 MHz Aviso S (Quantel Medical, Clermont-Ferrand, France) for 360-degrees around the ciliary sulcus looking for CBCs. The procedure is performed with a balanced salt solution filled ClearScan cover (ESI Inc. Minnesota, USA) over the tip of the ultrasound probe (Fig. 1). The ClearScan cover is comfortable for most patients due to its soft interface. This technique highly resolves soft tissue structures within a depth of 3 mm spanning 2 clock hours from the probe’s surface contact. Complete imaging of the ciliary body and sulcus is obtained with a series of transverse cuts, starting at the horizontal meridian, and progressing clockwise at 1 ½ clock hour intervals (i.e., 10:30–4:30, 12:00–6:00, 1:30–7:30) (Fig. 2).

Image of the 50 MHz Aviso S ultrasound biomicroscopy (UBM) probe with ClearScan cover. Top, Probe with ClearScan cover before assembly. Left, Disposable Clearscan Cover filled with balanced salt solution. Right, during contact of the anesthetized eye, care is taken to open the lids without applying pressure to the globe

Screening protocol for ciliary body cysts (CBCs). Left, White numbered areas show the scanning sequence and approximate ultrasound imaging depth used to create a 360° map of all ciliary body cysts. A 1 mm square grid is overlaid (yellow lines) and clock hours are indicated (red numbers). Right, Screening map with implantable collamer lens (ICL) image overlaid depicting a 1 × 2 mm sulcus cyst at 1 o’clock (brown oval) and a 1 mm cyst confined to the ciliary body at 6 o’clock (green circle)

An echo-free, round or oval fluid-filled lesion detected in the ciliary body or sulcus was defined as a cyst. The number, size (horizontal and vertical diameters) and location by clock hour and anatomical location were measured and documented on a 2–dimensional map (Fig. 2). Cyst characteristics were further defined and recorded according to whether there was protrusion into the ciliary sulcus.

Quantitative measurement of the sulcus is then taken with the Compact Touch STS UBM (Quantel Medical, Cournon d’Auvergne, France) via a centered axial cut. The device measures the sulcus-to-sulcus (STS) diameter, aqueous depth (AQD), and distance between the STS plane and anterior crystalline lens surface (LC) (Fig. 3). All UBM examinations were completed by the same, experienced ultrasonography technician (KQ).

Axial ultrasound biomicroscopy (UBM) measurements of a right eye. A = Sulcus-to-Sulcus, B = Distance between the STS plane and anterior crystalline lens surface, C = Aqueous depth, D = Interior chamber angle. UBM with probe position = 9:00, gain = 110 decibels, dynamic range = 60 decibels, total gain control = 15 decibels

The inclusion criteria for ICL placement were: 21–45 years of age, desire for spectacle and contact lens independence, stable refraction ≥ 1 year, AQD ≥ 2.8 mm, ECD ≥ 2200 cell/mm2, stable corneal tomography, gonioscopy grade ≥ III in all 4 quadrants, and no history of cataract, glaucoma, uveitis, or uncontrolled diabetes. Lens power calculations were performed considering the patient’s manifest and cycloplegic refraction using the manufacturer’s calculator (https://ocos.staarag.ch). A lens sizing calculation is performed with the manufacturer’s nomogram, which utilizes manual corneal white-to-white and AQD measurements. We also consider two external nomograms for ICL sizing recommendations. The Kojima ICL sizing nomogram is based on STS diameter, AQD and LC measurements [14]. The Dougherty ICL sizing nomogram is based on STS diameter and ICL power [15]. Final ICL size was at the discretion of the surgeon selecting the ICL closest to the average of the recommendations from all 3 sizing nomograms.

All ICL surgeries were performed by 4 experienced surgeons. The surgical procedure was performed through a 3.2 mm temporal corneal incision and 1 or 2 paracenteses as per surgeon preference. The anterior chamber was filled with a cohesive viscoelastic (Microvisc 1%; Bohus Biotech, Sousel, Portugal). A VICMO (spherical) or VTICMO (toric) ICL was inserted into the anterior chamber with an injector cartridge and implanted into the ciliary sulcus within the horizontal meridian. For toric ICLs, rotation to the recommended axis is performed using a digital intraoperative guidance system (Callisto, Carl Zeiss Meditec AG, Jena, Germany) from a preoperative reference image. Subsequently, viscoelastic is removed from the anterior chamber using a balanced salt solution. Acetylcholine 1% (Miochol®, Novartis, Camberley, UK) is instilled intracamerally to constrict the pupil, and compounded intracameral Cefuroxime 1 mg/0.1 mL is injected for infection prophylaxis prior to final hydration of corneal wounds. Postoperative follow-ups were performed at approximately 1 day, 1 week, 1-, 3-, 6- and 12-months following surgery. Postoperative evaluation included UDVA, CDVA, MRSE, IOP, slit lamp examination and ICL vault measurement via anterior segment ocular coherence tomography (Heidelberg Engineering, Heidelberg, Germany).

Statistical analyses were performed using Microsoft R Open (Microsoft Corporation [2020]. MicrosoftR: Microsoft R umbrella package. R package version 4.0.2.) and R Studio (RStudio Team [2021]. RStudio: Integrated Development Environment for R. RStudio, PBC, Boston, MA). Unadjusted descriptive statistics were reported for the sample overall, and by subgroups of patients with and without CBCs. Unadjusted group comparisons on continuous and dichotomous variables were made using t-tests and logistic regression respectively. To examine the relationship between an outcome and a set of predictors, we utilized multivariate fixed effects linear or logistic regression models to estimate the partial regression relationships. For eyes that underwent ICL placement, temporal trends among surgical patients were studied using linear mixed effects models. Further, likelihood ratio tests were used to check if CBC presence as a parameter improved the fit of the linear mixed effects models for post-operative outcomes (UDVA and IOP). In most instances, a two-tailed alpha of 0.05 is used to determine statistical significance, aside from AQD in which case one- and two-tailed tests were performed.