The light adjustable lens (LAL), since being introduced by RxSight in 2019, has revolutionized cataract surgery. As the first and only FDA-approved adjustable lens, the dioptric power can be changed +/- 2 D postoperatively, with the added ability to treat up to 2 D of astigmatism. While it almost seems too good to be true, it has delivered refractive outcomes that rival modern corneal refractive surgery. For presbyopic patients in search of relief from reading glasses, the LAL also boasts the ability to provide functional range of vision with little distance compromise. Reading glasses will still certainly be necessary for small tasks, similar to most presbyopia-correcting lenses. A key difference, however, is that the LAL does not induce glare or halos. The LAL+ is the newest addition to the LAL family, and it pushes the boundaries of visual range further with even less compromise.

Postop Is the New Preop

With traditional intraocular lenses (IOLs), refractive results are fully dependent on preoperative biometry. Each eye is unique, and there are several variables that drive surgical planning. However, even with the latest formulas, we are prone to refractive misses. The attempt is to pick a lens design and power that will serve a unique set of visual demands. While we like to think we’re very accurate, it’s not uncommon that we (and ultimately our patients) are forced to manage the consequences of residual refractive error or unwanted visual dysphotopsias.

The solution is to alter the lens power after it’s implanted. LAL surgery is just like any other cataract surgery: the IOL is implanted into the capsule in the normal fashion. The real difference comes at least 17 days after surgery. At this point, the eye should be mostly healed, and the lens has settled into its final effective lens position. Patients then undergo up to 3 light adjustments, followed by 2 mandatory lock-ins. The light adjustments involve exposing the IOL to precisely targeted ultraviolet (UV) light through a dilated pupil. The LAL is composed of UV-activated silicone that reacts to UV light at 365 nm.¹ This exposure causes changes in shape and power. These visits are usually separated by at least 1 week, allowing the patient time to “test drive.” In a way, we are no longer fitting a patient to the lens—the paradigm has shifted. Now we’re fitting the lens to the patient, customizing it to individualized needs.

The Search for the Holy Grail

Full, uncompromised vision at distance, intermediate, and near without glasses is the holy grail. While it remains elusive, we seem to be closer than ever. The LAL is not a multifocal or enhanced depth of focus (EDOF) IOL in the traditional sense—there is no splitting of light to increase visual range. Instead, the defocus curve is broadened through a precisely calculated spherical aberration. Surgically, the target is recommended to be plano for both eyes regardless of ultimate goals. This process allows us to move in a myopic direction during the adjustment process, which has a unique advantage. The LAL has an aspheric design, which lends itself to a small amount of EDOF in its unaltered state. On the first adjustment, we have an option to further broaden defocus by adding a small amount of negative spherical aberration (around 0.50 D). This adjustment is only possible if moving in the myopic direction and can only be done on the first adjustment. With such a small amount of negative spherical aberration, there is little to no qualitative visual compromise, preserving a comfortable “blend.” In our clinic, we avoid the term “monovision.” Compared to true monovision, the nondominant eye does not have to be set as myopic to achieve functional near vision.

Even with a plano target, patients achieve some ability to see at near or intermediate due to the asphericity of the lens. In fact, according to a recent study, in patients with bilateral plano targeted eyes, 88% saw J3 or better at near. While reading glasses will still help with magnification, this usually equates to uncorrected ability to see a computer or large printed items. In the same study, patients who chose blended vision (with 1 eye set at -0.25 D or more), 99% were J3 or better, while 56% were J1+ or better.² These results are similar to what we see in our clinic. The amount of myopia induced in the nondominant eye is completely customizable and tailored to individual demands. Interestingly, because of the broadened depth of focus, it’s not uncommon for patients with a -1.00 D target to be 20/25 or better at a distance in that eye.

The LAL+ is the latest option for presbyopic patients. Identical in basic design to its predecessor, the LAL+ contains a small central zone of increased power. This broadens the defocus curve further, while shifting it slightly in the myopic direction. This shift means improved near vision with no perceivable distance visual compromise. We are seeing much improved depth perception clinically—our patients tolerate the offset very well with few to no complaints of anisometropia. In a recent study comparing the LAL to the LAL+, the average distance visual acuity was 20/16-1.5 in the LAL group and 20/20+2.5 in the LAL+ group. Because of the shift in the defocus curve, we may give up a letter or two at distance technically. This compromise has not been observed clinically. At near distances however (40 cm), the LAL+ shows a whole line improvement compared to the LAL, consistent with what we’ve observed.³

The LAL and LAL+ are not for the impatient patient. Adjusting to them is admittedly a process. Surprisingly, this is not a deterrent. Patients genuinely appreciate the ability to directly participate—it adds a comforting sense of control for many. With the LAL+, the advantage of improved near vision with less anisometropia is clear and obvious. In our clinic, an unanticipated advantage has been improved efficiency. Usually, the number of total adjustments needed is dependent on the near eye target. With the LAL+, on average, we are achieving near function in 1 less adjustment than with the original LAL.

Maximizing Outcomes

While the LAL+ shows significant advantage, especially at near, the original LAL still has a place in our practice. With the added central aspheric zone of the LAL+, we are naturally inducing higher order aberrations. In eyes that are already highly aberrated (post refractive keratotomy, keratoconus, etc.), we lean toward the original LAL because of the shifted defocus curve. The LAL performs very well in these patients. We are often pleasantly surprised with the level of UCNVA patients with irregular corneas attain, even with a plano-targeted treatment.

With most presbyopia-correcting lenses (multifocals or EDOF IOLs), it’s often advisable to avoid using them for patients with less-than-perfect corneal or macular health. The concern is a resultant reduced visual quality or contrast sensitivity because of induced higher-order aberrations. The LAL and LAL+ are monofocal lenses, so we use them as such. In our experience, we have had excellent outcomes in patients with macular pathology and even severe glaucoma. In these cases, we again would lean toward the original LAL due to the potential impact of even small amounts of negative spherical aberration. It’s important to discuss with patients that the controllable variable is the resultant refraction, and there still are potential limitations due to concomitant pathology. However, the ability to customize outcomes still is a significant advantage, even if the visual acuity potential is less than 20/20.

Little Things Make a Big Difference

While the addition of increased central power makes marginal improvements, it has proven substantial for patients in our clinic. In the world of optics, there is no such thing as a free lunch. The LAL+ pushes the limits of visual range and quality. We are seeing impactful improvements at near with no compromise to distance visual quantity or quality. 

NICHOLAS J. BRUNS, OD, FAAO Dr. Bruns is lead optometrist at Summit Eye Care in Milwaukee, WI, where he serves as director of practice development. His clinical focus is pre-/postoperative care and ocular disease. He is also an adjunct clinical assistant professor at the Michigan College of Optometry.

References

1. LAL Summary of Safety and Effectiveness. US Food and Drug Administration; 2017. Accessed May 2, 2024. https://www.accessdata.fda.gov/cdrh_docs/pdf16/P160055B.pdf

2. RxSight Combined PMCS-001 & PMCS 002 Clinical Outcomes of Patients Bilaterally Implanted with LAL.

3. RxSight PMCS 007 Clinical Outcomes of Patients Bilaterally Implanted with LAL+.