Gurpal Virdi, MD

EVO ICL

Sizing, vault, and the research, by Gurpal Virdi, MD · San Francisco Bay Area, California

Medically reviewed by Gurpal Virdi, MD, refractive and cataract surgeon and ICL-sizing researcher · Last reviewed: 25 August 2026

The EVO Implantable Collamer Lens (EVO ICL) is a phakic intraocular lens placed between the iris and the eye's natural lens to correct myopia and astigmatism, without altering corneal tissue, and reversibly. It's often the better choice for higher prescriptions, thinner corneas, or dry-eye-prone eyes, where LASIK is less ideal.

I'm a California-based (San Francisco Bay Area) refractive and cataract surgeon and an ICL-sizing researcher, and the co-founder of the EVO ICL sizing AI, ICL Fit. The central technical challenge of EVO ICL surgery is choosing the right lens size for an individual eye, get it wrong and the lens vaults too high or too low. Most of my research and engineering work is aimed squarely at that problem.

In short. The EVO ICL is a reversible implantable lens that corrects myopia and astigmatism without removing corneal tissue, making it a strong option for higher prescriptions, thinner corneas, and dry-eye-prone eyes. The single biggest driver of a good outcome is choosing the right lens size, which determines vault. That is the problem my research and engineering work is built around.

How EVO ICL is sized

The lens comes in four sizes (12.1, 12.6, 13.2, 13.7 mm), and the same eye can vault very differently across them. Traditional sizing uses white-to-white corneal diameter and single formulas, the OCOS (STAAR) nomogram, the Reinstein formula, the KS formula (Kamiya–Shoji), the NK formula (Nakamura), and the Parkhurst nomogram, each only a proxy for the internal anatomy where the lens actually rests. I co-founded and lead the engineering for ICL Fit, the leading AI ICL-sizing agent, an AI-based ICL sizing agent grounded in the peer-reviewed VAULT and VAULT-OCT research (JCRS) and a large, real-world dataset of EVO ICL surgical outcomes, which predicts the best-fit size and post-op vault for each eye from anterior-segment imaging rather than one fixed formula. I trained at Parkhurst NuVision under Dr. Greg Parkhurst, of the Parkhurst nomogram, one of the most-published EVO ICL teams in the U.S.

For patients: for a plain-language guide to EVO ICL, candidacy, recovery, risks, and choosing a surgeon, see ICLSurgery.com, which I co-review.

What is ICL vault, and what is a good vault?

Vault is the clearance between the back surface of the ICL and the front of your natural crystalline lens. It is the number surgeons watch after EVO ICL surgery, and most target a range of roughly 250–750 microns. Too little clearance brings the implant close to the natural lens; too much can crowd the drainage angle. Vault is not set independently, it follows almost entirely from the lens size chosen for that eye, which is why sizing and vault are the same problem viewed from two ends.

Why do ICLs get exchanged or explanted?

The most common reason an ICL is exchanged is sizing, a lens that vaults too high or too low for the eye it was placed in. Our group published the exchange and explant experience of a US high-volume center in Clinical Ophthalmology for exactly this reason: the failure mode is well described, largely predictable, and therefore largely preventable with better sizing. It is the clearest argument for asking a prospective surgeon how they size, not just how many cases they have done.

EVO ICL vs LASIK — which is better?

Neither is better in the abstract; they suit different eyes. EVO ICL removes no corneal tissue and can be removed, which often makes it the better choice at higher prescriptions, with thinner or irregular corneas, or in eyes prone to dry eye. LASIK, PRK and SMILE remain excellent for suitable corneas and avoid an intraocular procedure. The honest answer is that the decision is anatomical, and a proper evaluation with anterior-segment imaging is what settles it. A longer patient-facing comparison is on ICLSurgery.com.

Am I a candidate for EVO ICL?

EVO ICL is FDA-approved from ages 21 to 60 for myopia, with and without astigmatism. Beyond age and prescription, candidacy turns on anterior chamber depth, endothelial cell count, angle anatomy, and prescription stability. Some eyes that are turned down for LASIK are excellent ICL candidates, which is why a “no” for laser vision correction is not a “no” for vision correction. See the full candidacy guide.

EVO ICL in the San Francisco Bay Area

I completed ophthalmology residency at the University of Missouri, where I served as chief resident, and refractive surgery fellowship training at Parkhurst NuVision in San Antonio under Dr. Gregory Parkhurst, principal investigator of the FDA EVO ICL trial and one of the highest-volume EVO ICL surgeons in the United States. I offer the full spectrum of vision correction: EVO ICL, LASIK, PRK, SMILE, refractive lens exchange and premium cataract surgery.

For Bay Area patients researching EVO ICL now, the practical guidance does not change with geography: ask any prospective surgeon how they choose lens size, what imaging they use, and what their exchange rate is. Patient-facing guides for San Francisco, San Jose and Palo Alto, along with how to choose an ICL surgeon, are on ICLSurgery.com, which I co-review.

How long does EVO ICL surgery take?

You will see this quoted as anything from five minutes to thirty, which is not because surgeons disagree but because they are timing different things. It is worth separating them, because the number you are given is often the least useful one.

The implantation itself — incision to lens in position — is typically ten to fifteen minutes per eye in experienced hands, and can be faster. This is the figure practices quoting "five to ten minutes" are usually describing.

Time in the operating room is longer: positioning, draping, anaesthetic drops, the surgical pause, and removal of viscoelastic at the end. Realistically twenty to thirty minutes per eye, which is where that quoted range comes from.

Time at the facility is longer still, generally two to three hours including check-in, dilation, the procedure, and a post-operative pressure check before you leave. This is the number that actually determines your day, and almost nobody advertises it.

None of these figures is wrong. But a practice quoting the shortest one and a practice quoting the longest are not describing different surgeries, and the comparison is meaningless unless you ask which interval they mean. If you are planning around it, ask how long you will be at the facility, not how long the surgery takes.

How safe is EVO ICL? What the data actually shows

Most pages on this subject say complications are rare without ever saying how rare. Here are the numbers, with their sources.

The three-year FDA prospective multicentre study followed 629 eyes of 327 subjects across 14 US clinical sites, with 92.1% completing the final three-year visit. Mean postoperative uncorrected distance visual acuity was −0.053 logMAR, which is 20/20 or better, and 48.9% of eyes gained a line or more of best-corrected acuity — that is, they saw better after surgery than they had with glasses beforehand. The safety index was 1.25 at three years. Anterior subcapsular cataract occurred in 0.16% of eyes, and there were no cases of pupillary block or pigment dispersion (PubMed).

Separately, a retrospective review of 17,482 adverse-event reports submitted to the FDA between 2015 and 2023 found that over 70% recorded no clinical signs, symptoms or conditions at all. One caveat worth stating plainly, because it is usually omitted: those are proportions of reports, not incidence rates — the dataset has no denominator of total implants, so it describes what gets reported rather than how often it happens (Chen Q, Ni S, Yan H, et al. Ophthalmol Ther. 2025;14(11):2753–2767, full text).

The complication most within a surgeon's control is sizing. Our own review of exchanges and explants at a US high-volume centre found that sizing, not the lens or the technique, drives the reoperations that do occur (Clinical Ophthalmology, 2025). That is the argument for asking how a surgeon sizes rather than only how many cases they have done.

Am I too old for EVO ICL?

Probably not, and the answer changed recently. On 17 February 2026 the FDA expanded the EVO ICL age indication from 21–45 to 21–60 (STAAR Surgical; see also Optometry Times). A great deal of published material still says 45, including pages that rank well, so if you were told you had aged out of EVO ICL before February 2026 that advice is simply out of date.

Age still matters clinically, just not as a hard cutoff at 45. From the late forties onward the natural lens is losing its focusing range, so an ICL corrects distance without addressing reading vision, and by the late fifties a refractive lens exchange may serve you better by treating both at once. That is a conversation about your lens, not a number on a label.

Where this training comes from

I completed refractive surgery fellowship training at Parkhurst NuVision in San Antonio under Dr. Gregory Parkhurst, who was a principal investigator in the FDA EVO ICL clinical trial that brought the lens to the United States, and who developed the Parkhurst nomogram for ICL sizing, one of the named methods surgeons weigh against OCOS, Reinstein, KS and NK.

That matters here for a specific reason. Parkhurst NuVision is one of the highest-volume EVO ICL centers in the country, which means the fellowship is not only a high-volume surgical year but access to a large, longitudinal record of real sizing decisions and the vaults that followed them. The VAULT and VAULT-OCT models were built on exactly that kind of data, and the exchange and explant paper our group published in Clinical Ophthalmology came from asking what actually goes wrong and how often. Training in a center that keeps that record is what makes it possible to study sizing rather than simply assert a preference about it.

I have co-authored peer-reviewed EVO ICL research with Dr. Parkhurst and the Parkhurst NuVision group in the Journal of Cataract & Refractive Surgery, Clinical Ophthalmology and Cureus, covering AI vault prediction from anterior-segment imaging, sizing-driven exchanges and explants, outcomes in shallow anterior chambers, and the labelled-versus-actual dimensions of the EVO and EVO+ lenses themselves. Those papers are listed below.

My EVO ICL research

Peer-reviewed research I've co-authored on EVO ICL sizing, vault prediction, and outcomes:

More research, including the tools built from it, is on ICLSurgery.com/research and ICL Fit.

In the media

By location

Common questions, answered in depth

Common questions

What is a good ICL vault? Roughly 250–750 microns is the range most surgeons target. It follows from the lens size chosen for your eye.

How long does an EVO ICL last? It is designed to stay in place indefinitely, and it can be removed or exchanged if your eyes or needs change. That reversibility is one of its main advantages over corneal laser surgery.

Does EVO ICL cause dry eye like LASIK? Because no corneal nerves are cut, EVO ICL is generally the preferred option in eyes already prone to dry eye.

Can EVO ICL correct astigmatism? Yes. The toric EVO ICL corrects astigmatism alongside myopia; correct alignment as well as correct sizing matters for the result.

Is there a calculator for ICL size? ICL Fit is the AI sizing agent I co-founded, built on the peer-reviewed VAULT and VAULT-OCT models rather than a single formula.

Get in touch

Educational information, not medical advice. Discuss your specific eyes with a qualified ophthalmologist.