As an ophthalmologist with over 25 years of experience in refractive surgery, I’ve seen the evolution of procedures like implantable collamer lenses (ICLs) transform how we correct vision. At SHARPEVISION, I have been blessed to perform more EVO ICL annually than any other surgeon in the US as of this writing. Outside the US, many surgeons implant thousands annually. In Asia, the EVO ICL is performed on about 80% of the overall patients undergoing refractive procedures.

The EVO ICL, developed by STAAR Surgical, is a superb option for patients with moderate to high nearsightedness with or without astigmatism. It’s also an excellent choice for those with preexisting dry eyes. In March 2022, the EVO ICL replaced the Visian ICL, bringing the United States to the same level of technology that the rest of the developed world enjoyed for a decade or more prior to the US FDA approval for the EVO. The EVO lens uses the same superb collamer material as its predecessor, and is the same shape.

The EVO has 3 major design improvements:

1. EVO has a slightly bigger optic than the Visian ICL, up to -12 power. If the required lens is higher than -12, the optic diameter is reduced slightly to account for the increased thickness.
2. EVO has more visible toric markings to allow for more precise alignment of the lens.
3. EVO, most importantly, has tiny holes in the lens to allow equalization of fluid pressure on either side of the lens so that iridotomy is no longer necessary.

The EVO ICL is a very thin, flexible lens placed behind the iris (the colored part of your eye) and in front of the natural lens of your eye. It focuses the light perfectly on the back of your eye without removing any tissue of your cornea like LASIK does. But one patient question that often comes up is the role of endothelial cell counts (ECC). This single cell layer lines the back of the cornea and maintains corneal clarity by pumping out excess fluid. Damage or loss can lead to edema and vision issues.

In this post, I’ll discuss the history of ECC in cataract surgery, its mandated role in FDA trials for the EVO ICL, and why, in everyday practice, many of us—including myself—don’t routinely measure them preoperatively. Drawing from a conference I attended in December 2023 with 150 fellow eye surgeons, I’ll explain why this step, while useful in research, and was required for the FDA approval, is unnecessary in the clinic.

The Historical Context: Endothelial Cell Counts in Cataract Surgery

To understand ECC’s relevance to the EVO ICL, we need to go back to its roots in cataract surgery. The corneal endothelium was first appreciated for its fragility in the mid-20th century, but it wasn’t until the 1970s that specular microscopy revolutionized our ability to count and assess these cells. Before that, surgeons relied on clinical signs, like corneal edema, to denote damage.

Cataract surgery, particularly the shift to phacoemulsification in the 1970s and 1980s, brought ECC into the spotlight. Phaco uses ultrasound to emulsify the lens, but this energy, along with irrigation fluids and mechanical trauma, can cause endothelial cell loss (ECL). Early studies, like those in the 1980s, reported average losses of 10-20% post-surgery, with higher rates in complicated cases or eyes with pre-existing conditions like Fuchs’ dystrophy. For instance, a 1980s review noted that eyes with low preoperative ECC (below 1,000 cells/mm²) were at risk for pseudophakic bullous keratopathy (PBK), a condition where the cornea swells irreversibly, necessitating a corneal transplant.

Over the decades, research confirmed that phaco was hard on the endothelial cell layer. A 1994 study found that even 10 years after cataract extraction, eyes lost endothelial cells at 2.5% per year—far exceeding the normal aging rate of 0.3-0.5% annually.  More recent work, such as a 2024 analysis, confirms progressive ECL post-phaco, emphasizing the need for preoperative assessment in at-risk patients. In Fuchs’ cases, surgeons now use viscoelastic devices and softer techniques to minimize loss, but ECC monitoring remains standard for high-risk eyes.

This history shaped how we think about intraocular procedures. Any surgery inside the eye risks ECL from inflammation, touch, or fluid dynamics. For cataract surgery, preoperative ECC helps predict outcomes and guide decisions—like opting for femtosecond laser assistance in dense cataracts. But as we’ll see, the leap to refractive lenses like the EVO ICL is different.

The FDA’s Stance: ECC in EVO ICL Trials

The EVO ICL received FDA approval in March 2022 for correcting myopia from -3 to -15 diopters, with or without up to 4 diopters of astigmatism. Unlike the Visian ICL models, the EVO features a central hole (aquaport) that improves aqueous flow, reducing risks like cataract formation and pressure spikes. But to get that approval, STAAR had to rigorously demonstrate safety, and ECC was a key metric.

In the FDA clinical trials, preoperative ECC was mandatory. Exclusion criteria often included counts below 2,000 cells/mm², as low ECC could heighten risks of postoperative loss. The trials tracked ECC over time, reporting a mean decline of just 2.2% at six months—far lower than typical cataract surgery losses. However, the labeling warns that some patients experienced 30% or greater loss, though rare. Three-year data from the trials showed stable ECC with minimal ongoing loss, and reduced anterior subcapsular cataracts compared to the Visian model.

Why the emphasis? The FDA requires robust data on corneal health for any implantable device, especially phakic ones that sit near the endothelium. The lens’s position demands adequate “vault”—space between the ICL and natural lens—to avoid contact. Too much vault could theoretically rub the endothelium, though the EVO’s design mitigates this. Trials used specular microscopy to quantify cells pre- and post-implant, ensuring no excessive ECL. This data was pivotal for approval, proving the EVO’s safety profile. ECC requirements were for trials, not post-approval mandates. The FDA doesn’t require ECC’s. In the clinical practice of medicine, doctors don’t do the same things, nor should they do the same, as would be done in an FDA trial.

Real-World Practice: Insights from the Front Lines

Fast-forward to December 2023. I was at a major ophthalmology conference with about 150 refractive surgeons from across the U.S. During a panel on ICL implantation, the topic of preoperative ECC came up. In a show of hands, zero surgeons reported routinely checking ECC before EVO ICL procedures. Why? It’s cumbersome, expensive, and difficult to interpret in a way that changes management. After 10 years of implanting both the Visian ICL prior to March of 2022, and the EVO ICL since then, there has never been a case of clinically significant endothelial cell loss, formation of corneal guttata (a sign of endothelial cell loss) in my practice, nor has it been reported in our peer-to-peer forums and discussions.

Measuring ECC requires specular microscopy, a specialized machine not every clinic has. It’s time-consuming for staff and patients, adding $100-300 to costs without reimbursement in many cases. Interpretation isn’t straightforward—normal counts vary by age (2,500-3,000 cells/mm² in young adults, dropping with time), and a “low” count might not predict issues in an otherwise healthy eye.

More importantly, it has never affected the decision to proceed in my practice. We look for signs of low endothelial cell counts-namely corneal guttata. The EVO ICL’s safety data is solid: Studies show endothelial cell loss rates under 3% long-term, comparable to natural aging. In my practice, I’ve implanted thousands of EVO ICLs without preoperative ECC, and postoperative monitoring (when done) shows no concerning trends. Conference peers echoed this: No evidence suggests routine ECC prevents complications, nor has there been a case of corneal transplant due to endothelial cell loss after ICL; and the ICL has been implanted in over 3 million eyes as of this writing. The material is the same as it was 30+ years ago, and the design is only mildly different than it was 30 years ago. Vault prediction relies more on anterior chamber depth (ACD), white-to-white measurements, and tomography—not ECC.

Recent literature supports this shift. A 2024 paired-eye study on EVO ICL found no significant ECD differences between high- and low-vault groups, with preoperative means around 2,700 cells/mm².  Another 2025 analysis compared ICL types and reported stable ECD at one year, without mandating preoperative checks in clinical settings. Guidelines from bodies like the American Academy of Ophthalmology don’t require it for routine ICL cases, reserving it for research or high-risk patients (e.g., history of uveitis or shallow ACD).

Weighing the Pros and Cons: Is ECC Measurement Necessary?

Proponents argue that preoperative ECC baselines future monitoring, especially if complications arise. In trials, it was required to exclude potentially vulnerable eyes, and some international protocols still recommend it for medico-legal reasons. But cons outweigh pros in standard practice. The EVO’s aquaport reduces cataract risk (zero in trials), and ECL is minimal.  ECCs add nothing, and doesn’t improve outcomes. To quote a colleague at the conference, “If it doesn’t change what I do, why do it?”

Exceptions exist: For older patients considering cataract surgery (they aren’t EVO candidates anyway), or family history of corneal dystrophy, it may be useful, to advise on surgical risks. But for the typical 20-40-year-old myope there is no utility in the testing.

Conclusion: Prioritizing Patient-Centered Care

The history of ECC—from 1970s cataract surgery in the early days of phacoemulsification, and usefulness in corneal transplant surgery, to FDA trial rigor—reveals the commitment to safety of the ophthalmology profession. For the EVO ICL, it was essential for approval, but in 2025’s clinical landscape, it’s a relic of research protocols. My conference experience reinforced that we’re evidence-based: No reason to measure if it doesn’t impact decisions.

In my opinion, the EVO ICL is a very exciting evolution in the field of refractive eye surgery. In our practice, we recommend EVO ICL for anyone who is a candidate. It solves many of the limitations of laser vision correction (LASIK and PRK):

The EVO ICL:

• has no dryness risk
• requires no corneal tissue removal
• is very accurate
• is not dependent on corneal thickness- if you weren’t a candidate for LASIK/PRK, you may be an excellent candidate for EVO ICL
• allows correction at much higher degrees of nearsightedness
• provides excellent night vision
• is very stable long-term
• is removable, which is typically done only when cataract surgery is needed in our 60+ year-old patients
• has a UV light filter which may reduce the risk of both macular degeneration and cataract formation
• causes no pain during or after the procedure
• has no need to ever be replaced- the material has been in eyes, in cases outside the US, for close to 30 years at this point with no side effects.

Book your appointment for a free EVO ICL consultation at sharpe-vision.com