As with many constructs that we have previously grown accustomed to, with advancing technology, lines are blurring more than ever before between what we have previously defined as distinctly different types of intraocular lenses (IOLs) used for cataract surgery. It used to seem very simple—we had monofocal lenses, and we had multifocal intraocular lenses (MFIOLs). Then, accommodative lenses came to the market. Later we had the introduction of a new category, extended depth-of-focus lenses, with the Symfony (although, many argue that this is not a pure EDOF lens but rather a hybrid diffractive EDOF/MFIOL). And since that time, we have had many more new intraocular lenses introduced which don’t fit neatly in any one specific category.
Intraocular lenses compared
No lens technology is a perfect replacement for the natural crystalline lens. But the modern cataract surgeon has many options on the market to meet their patients’ individualized visual needs and goals. Generally speaking, EDOF intraocular lenses elongate the depth of focus around a single focal point, which gives patients more range than a monofocal lens, but not quite as much as multifocal lenses, which have two or three focal points. Compared to MFIOLs, EDOFs typically allow for better contrast sensitivity and less glare and halos, however they also typically have less robust near vision. Some surgeons will circumvent this by employing mini-monovision.
Despite the incredible advancements in our intraocular lens technologies, one of the few things refractive surgeons can generally agree on is that no EDOF or MFIOL can exactly match the contrast sensitivity and crisp quality of distance vision quite as well as a monofocal lens implant.
There is always some sort of compromise one must make when selecting an intraocular lens technology. Modulation transfer function (MTF) characterizes the image quality of a lens, particularly as it relates to contrast and how much of it is retained from object to the image. To increase depth of focus (aka the range of vision) of a lens, there will be less MTF and thus, contrast loss. To minimize this, one can select a monofocal lens, however you of course lose that extended range of vision.
Patient considerations with IOLs
This is why patient education and selection is critical to ensure you are selecting the appropriate lens to meet your patients’ visual goals and needs. Especially with patients considering a EDOF or MFIOL lens implant, it is imperative to understand what their daily tasks and activities may entail. Many refractive surgeons also find that personality types can also be another way to gauge how appropriate a patient may be for a certain type of lens, with the thought that many highly observant and particular patients (aka Type-A personalities) are generally less able to tolerate the subsequent glare and halos that one can appreciate after having an EDOF or MFIOL implanted.
Of course, above all else, the overall health of the eye is most critical to determine candidacy for a premium lens. Patients with significant retinal pathologies, glaucoma, or ocular surface pathologies are not classically ideal candidates. However, with mild pathology and considering what are generally thought to be more forgiving lenses like the monofocal Eyhance or perhaps even the Vivity (Alcon, Fort Worth TX), some surgeons have come to reconsider what constitutes a true contraindication for these advanced lens technologies.
Although there are many ways to categorize current intraocular lens technologies, Figure 1 illustrates a schematic of representative lens types which illustrates the details that determine the range of focus of each particular lens.
There are three basic strategies generally used to increase depth of focus for classic EDOFs currently used in the US:
1) Harnessing spherical aberration.
2) Manipulating chromatic aberration.
3) Using the pinhole effect.
However, hybrid EDOF/MFIOL lenses will employ multiple strategies including having multiple focal points.
FDA-approved extended depth-of-field lenses
Currently, there are only three IOLs formally approved and categorized in the US by the FDA as EDOF lenses. The defining criteria for what constitutes an EDOF as per the FDA is “one that uses an optical design (e.g., through aspheric shape, use of more than one refractive zone, or diffractive technology) that provides a continuous range of relatively clear vision, beyond that achievable with the optics of a monofocal lens.
EDOF lenses may have one or more focal points with any additional focal points or any significant light energy (on the optical axis) restricted to within 1.5 diopters (at the corneal plane) of the focal point associated with the labeled power when tested with a 3mm aperture.”1
EDOF intraocular lenses
- The Symfony (ZXR00) was the first of its class on its introduction into the US market in 2016. The anterior surface of the optic is aspheric, with the posterior being an achromatic diffractive surface with an Echelette design grating.
- Vivity was the second EDOF IOL approved by the FDA, and is notable for being the 1st non-diffractive EDOF lens via its proprietary X-Wave technology.
- The Acufocus lens (IC-8 Apthera) is newest EDOF approved by the FDA in July of 2022, and it utilizes the pinhole effect to increase depth of focus by way of a 1.36 mm central aperture surrounded by a 3.23 mm nondiffractive opaque mask.
The intraoperative picture in Figure 2 shows an implanted Symfony Toric that illustrates the diffractive surface with Echelette design grating. As with MFIOLs, when using EDOFs, for optimal visual outcomes, it is important to address any significant corneal astigmatism and also ensure the lens is well centered.
Figure 2
Although some may think of the Tecnis Eyhance as an EDOF, it is not categorized as one but rather is an advanced monofocal with a higher-order aspheric lens. It is thought to have good image quality as with other monofocal lenses, but has the benefit of some intermediate vision as well. The Tecnis Synergy is a hybrid MFIOL/ EDOF lens which both elongates the range of focus via refraction and also uses diffraction with multiple focal points. It is thought to have the benefit of a trifocal lens, but harnesses the EDOF technology to dampen glare and halos.
Tips and takeaways
For young eye surgeons, or perhaps more seasoned attendings who have yet to dip their toe into the EDOF/MFIOL waters, becoming familiar with all of these various advanced intraocular lens options can seem daunting. However, as with any new technology that you begin to offer your patients, patient selection truly is key. Early on, it is prudent to be very picky about which patients you may offer these advanced lens technologies to. Hyperopic patients tend to be among the happiest.
The ideal patient also has, aside from the cataract, an otherwise healthy eye including a pristine ocular surface. The air-tear film contributes the bulk of the refractive power of the eye, and an intact surface not only is important for obtaining good quality and accurate preoperative measurements, it’s important for the advanced lens technology to work well in vivo.
To best set yourself up for success, make sure to invest adequate time counseling your patients and setting appropriate expectations on visual outcomes, particularly when it comes to possible glare and halos and decreased contrast sensitivity. Remember, an ounce of prevention is worth a pound of cure.
References
- “Product Classification: Extended Depth of Focus Intraocular Lenses.” Food & Drug Administration.https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpcd/classification.cfm?id=4583. 25 Jul 2022.
- Kanclerz P, Toto F, Grzybowski A, Alio JL. Extended Depth-of-Field Intraocular Lenses: An Update. Asia Pac J Ophthalmol (Phila). 2020 May-Jun;9(3):194-202. doi: 10.1097/APO.0000000000000296. PMID: 32511121; PMCID: PMC7299221.
- Corbelli E, Iuliano L, Bandello F, Fasce F. Comparative analysis of visual outcome with 3 intraocular lenses: monofocal, enhanced monofocal, and extended depth of focus. J Cataract Refract Surg. 2022 Jan 1;48(1):67-74. doi: 10.1097/j.jcrs.0000000000000706. PMID: 34054077.
- Mencucci R, Cennamo M, Venturi D, et al. Visual outcome, optical quality, and patient satisfaction with a new monofocal IOL, enhanced for intermediate vision: Preliminary results. J Cataract Refract Surg. 2020;46:3:378-387.
