Pearls for success with full-range diffractive IOLs

Over the course of the past decades, our IOL technology has continued to improve, particularly with the ability to address presbyopia.

Today we are fortunate to have three FDA-approved diffractive IOL designs that provide a full range of uncorrected vision for our cataract surgery patients. With these new options, we anticipate a greater uptake and patient acceptance to the benefits of these IOL designs.

Older design refractive multifocal IOLs were phased out about 20 years ago as new diffractive technology models came to market. These new designs provided two distinct focal points, one for near and the other for far. This worked well, and the higher add power helped to separate the two focal points to minimize dysphotopsias. We soon realized that having a near point that was so close was limiting, and then lower add IOL options became popularized.

Today we want a full range of great vision for our patients without dependence on glasses. This requires designs that extend the range from near vision (30 cm) to intermediate vision (60 cm) and then beyond 100 cm for distance vision. To achieve this, we can adopt different diffractive IOL designs such as trifocal or those that are bifocal with extended depth of field. The net result to patients is great vision for all functional ranges without glasses.

Patient selection for these IOLs is of paramount importance because they use optical engineering to provide the full range of vision, which is different from the youthful accommodation of the crystalline lens.

The concept that resonates best with my understanding of the physics is that the number of photons is fixed. This means that if I am outside walking in the moonlight on a nice summer evening, I cannot make the moon brighter. Whatever light exists in my environment is fixed, and if I focus it all at a narrow range vs. a wider range, this will affect the light distribution. Keeping in mind that retinal sensitivity tends to decrease with age, we need to carefully consider the patient’s expectations.

Patients with significant cataracts where a large portion of the incoming light is scattered or absorbed by the media opacity are much easier to please. Imagine a patient with an opaque white cataract or a dense brunescent cataract: Anything is an improvement, and these patients will be amazed with any IOL choice. On the other hand, consider a patient who has zero cataract and instead wants to exchange the crystalline lens for a diffractive full-range IOL in order to address presbyopia. This is far more challenging due to patient expectations.

Look at the cataract of the patient and determine what percent of the incoming light is scattered or lost due to the cataract. If this value is significant, then the patient will be happy with any IOL and will potentially be thrilled with a full-range diffractive IOL.

The other important consideration is the patient’s preoperative refraction. For patients who are plano presbyopes without cataracts, there is no perfect IOL that will make them young again. A 55-year-old plano presbyope who desires refractive lens exchange with a full-range diffractive IOL is a big challenge. A patient like this may already have 20/20 distance vision with very high optical quality, only desiring to address the presbyopia without affecting the distance vision. That is a challenge because these IOL technologies may not be able to provide the same distance vision, particularly at night, compared with the clear crystalline lens.

Another similar challenge is the 55-year-old patient without cataractous changes who is a –2 D myope. This patient tells you to just fix her distance vision because her near vision is already great. This is not the same as a 25-year-old –2 D myope who wants LASIK because this young patient still has a huge degree of accommodation. For this patient, the refractive status of –2 D provides amazing near vision that no other 55-year-old patient has and that no diffractive IOL can deliver while aiming for plano.

Now consider the patient who is 55 years old but is a +3 D hyperope with no cataractous changes. This patient is impaired at all ranges of vision currently, using +3 D for distance vision and then +5 D for near vision. If we implant a full-range diffractive IOL in this patient, the improvement in vision will be dramatic, and the patient will be happy.

For the new generation of full-range or trifocal diffractive IOLs, as long as we choose patients who have significant lens opacities and/or have favorable refractive errors, we can deliver an improvement in vision that is sure to make them happy.

For a video of this topic, please visit https://cataractcoach.com/category/refractive-surgery-refractions/.

• For more information:
• Uday Devgan, MD, in private practice at Devgan Eye Surgery and a partner at Specialty Surgical Center in Beverly Hills, California, can be reached at devgan@gmail.com; website: www.CataractCoach.com.

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Disclosures:
Devgan reports owning CataractCoach.com, which is a free teaching website.

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