Presbyopia management has been the holy grail for intraocular lens technology development for 30 years, but sub-classifying lenses has become confusing and ad hoc, says Dr Peter Sumich. He offers a way out.
As biometry became predictable and 90% accurate for achieving reliable emmetropia, intraocular lens (IOL) companies geared their development teams towards solving the presbyopia puzzle. Right from the start the goal has been to maximise near vision while minimising unwanted side effects.
I approached this brief review to describe the current approaches to presbyopic IOLs in an agnostic, non-manufacturer specific way. For simplicity, we start with the three common paradigms.
The first is monofocal monovision that works well for those who accept anisometropia and variable reduction in stereopsis, somewhat proportional to the degree of monovision.
The second is diffractive multifocal technology which has the most potent benefit for presbyopic relief but common and well-described photic side effects.
The third and most recent paradigm is extended depth of focus (EDOF) technology which extends the depth of focus through a variety of optical means. EDOF implants, whilst not providing as much presbyopic benefit as diffractive light splitting, do hit the sweet spot for lifestyle vision with little downside for photic side effects and are the fastest growing category.
But with so many companies working on so many solutions it has become evident that we have nomenclature confusion.
In a recent edition of the Journal of Cataract & Refractive Surgery (JCRS), Professor Ribiero’s group suggested a new framework towards a common language to describe presbyopic lens performance1 (Table 1).
The IOLs are also diagrammatically described in Figure 1 .
A common language helps clinicians, researchers and patients to understand what we are using, how they treat presbyopia and how we can compare lenses.
In general, every surgeon will have a preference for the type of presbyopic implant they use and understand. Fine-tuning and tweaking these implants takes only a short time but has been extremely rewarding for our patients who are seeing great lifestyle benefits. Most patients will still use occasional spectacles for fine tuning of nearer vision or night driving but in most cases they are functionally spectacle independent for their day-to-day home activities such as cooking, cleaning and gardening. Other prized benefits usually achievable are Google Maps when driving, mobile phone, social media and iPad use.
The implants need to be individualised to the patients visual demands with their expectations and tolerance for unwanted side effects factored in. Mix and match approaches are sometimes used and varying degress of mini-monovision are often successful.
Understanding defocus curves is essential to appreciating the performance graphs in Figure 2.
One can conceptualise these as the range of near vision over which a 6/6 equivalent is possible. At one extreme is the ‘Narrow’ range of field representing a monofocal IOL. At the other extreme is the steep transition over a wide range offered by a high add diffractive bifocal lens which gives excellent close vision but bothers computer users and one Lego fanatic who modelled at arms length and made my life hell.
A smoother transition, without the missing intermediate vision, is provided by a trifocal lens. The ‘Enhance’ and ‘Extend’ EDOF categories describe the ‘mini EDOF’ and ‘maxi EDOF’ which extend the depth of focus to a lesser or greater extent respectively.
My patients are generally accepting of the need for reading glasses for phone banking, pill bottles and phone bills. It is always important to remind even refractive surgery patients who expect the most, that such occasional spectacles are usually required, because it sets expectations to a manageable level. However in many cases patients surely are complete in their independence – but it is foolish to promise. Also noteworthy is the unexplained individual variation in presbyopic outcomes which defies optical explanation.
The role of optometrists is largely to counsel patients that presbyopic IOL solutions are available to a greater or lesser extent. Rather than getting lost in a deep dark hole trying to explain the technologies, the simplest approach is to broadly outline the issues of presbyopia and instill a reasonable level of expectation. I ask my patients to return to their optometrist for refraction at one month, but many patients will resist the need for an immediate reading script until six months of exploring their newfound vision. At that six-month stage they give in more willingly to the reality that occasional glasses are necessary. So don’t forget the six-month review to follow up on the patient who rejects readers at the one-month refraction.
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Reference:
1. Ribeiro, Filomena MD, PhD; Dick, H. Burkhard MD, PhD; Kohnen, Thomas MD, PhD; Findl, Oliver MD, PhD; Nuijts, Rudy MD, PhD; Cochener, Beatrice MD, PhD; Fernández, Joaquín MD, PhD. Evidence-based functional classification of simultaneous vision intraocular lenses: seeking a global consensus by the ESCRS Functional Vision Working Group. Journal of Cataract & Refractive Surgery 50(8):p 794-798, August 2024. | DOI: 10.1097/j.jcrs.0000000000001502
