Precision strategy: Optimizing visual outcomes with advanced small-aperture lenses

A recent Ophthalmology Times Case-Based Roundtable addressed the pathway to achieving optimized visual outcomes using an advanced small-aperture IOL (IC-8 Apthera; Bausch + Lomb Surgical). Mark Lobanoff, MD, an ophthalmologist in St Louis Park, Minnesota, shared the highlights of the discussion.

US ophthalmologists have long anticipated a small-aperture IOL technology because it functions as a pinhole-based optical system. It blocks distorted, unfocused peripheral light and only allows light that comes in directly tangential to the corneal surface. This focusing effect creates an extended depth of focus (EDOF), he explained. Lobanoff described some cases that demonstrated the advantages, pitfalls, and factors to consider when using this IOL.

Case 1

A 48-year-old woman desired a refractive lens exchange to replace a Light Adjustable Lens (LAL; RxSight, Inc) and to achieve spectacle independence. Distance correction was 0.75 D
of astigmatism in the right eye, with a little mixed astigmatism –0.75 D +1.50 x 155 in the left eye. Her lifestyle included computer work and nighttime activities and required her vision to be as free of glare as possible.

“These visual needs eliminated implantation of a trifocal or another EDOF [lens], and we chose the IC-8 as the long-term solution,” Lobanoff said.

Imaging showed a “fairly normal” retina. However, evaluation of the astigmatism in the right cornea showed greater astigmatism in the 3-mm central zone than across the wider corneal field in the 5-mm zone. This was a significant decrease in the astigmatism across the entire cornea. “This is important when considering IOLs that might be effective,” he explained.

Another consideration is that the patient resided in Florida. Although the referring surgeon implanted the LAL, Lobanoff was concerned about the LAL shield’s breakdown over time in a sunny environment. The patient’s history showed that after the first LAL adjustment was performed, the vision worsened to 20/30^–2, with increased hyperopia and cylinder.

The bottom line was that the patient did not see well despite a second LAL adjustment and a YAG laser for posterior capsular opacification. Because the patient reported quadropia plus significant ghosting, the first surgeon performed topography-guided LASIK. However, the patient did not have significant higher-order aberrations in the cornea. Two weeks post LASIK, the patient reported terrible distance vision for driving, inability to read, constant ghosting/blurring, and good intermediate vision. Following a LASIK enhancement, the patient was referred to Lobanoff.

Finding the problem

Lobanoff recounted that the first step was to determine where the problem was in the eye.

The corneal topography looked essentially normal, and the ocular measurements, aqueous depth, and pupil size were relatively normal. The astigmatism was 0.99 D across a 7-degree axis.

He explained that in some patients with LALs, there may be a minute residual refraction error. However, visual problems arise because the polymerization of the monomers by the ultraviolet light may have been incomplete or not smooth and uniform.

“There may be pockets of polymerized macro- or monomers,…areas that are not polymerized, and perhaps a shift in the refractive index from one part of the lens to the next, leading to poor optics,” he explained.

The solution was simple. When he provided the patient with a pinhole occluder to look through, she described her vision as crisp and clear at all distances. The small-aperture IOL can mimic the vision obtained with the pinhole occluder. Implantation of the IOL in this dissatisfied patient resulted in 20/20 uncorrected vision.

Case 2

A 50-year-old man had a history of keratoconus treated with cross-linking and topography-guided photorefractive keratectomy (PRK) in his left eye a few years previously. The keratoconus had remained stable after cross-linking.

The macular status is a consideration when the small-aperture IOL may be an option because the incoming light is directed to the foveal region.

In this case, there was
0.3 D of astigmatism at an axis of 120. However, Lobanoff observed that the 3-mm zone in the left eye had significantly more astigmatism than the Pentacam (Oculus) had revealed—1.63 D—in both the 3- and 5-mm zones at very different axes. The small-aperture IOL can mask up to 1.75 D of astigmatism.

Another problem was that the patient had a complex eye, and a future PRK was a possibility. In this case, an adequate corneal thickness is required.

Given the data used to calculate this lens power, there was 1.26 D of astigmatism at 88 degrees. Lobanoff explained that he targeted –0.66 D because the defocus curve of the small-aperture IOL, when set to a target of 0, has a tail that corrects a lot of myopia to approximately –1.5 D, but it also corrects into the hyperopic range.

In this case, Lobanoff shifted the defocus curve slightly myopic and, by choosing a target close to –0.7 D, achieved good distance and intermediate vision. By extending the curve to myopia, the reading ability improved. This was for the nondominant eye in this patient. For the dominant eye, stronger distance vision is desired, and the target in the dominant eye is approximately –0.25 or –0.3 D.

Two months postoperatively, the vision was 20/20 uncorrected, and the lens masked the astigmatism. However, the patient complained of ghosting, which is a quality issue. The central astigmatism had actually increased, probably because of the cataract incision.

Lobanoff performed PRK to correct the ghosting, aiming to target the central astigmatism. Postoperatively, the vision remained 20/20 with J1 near vision.

Pearls

Lobanoff advised surgeons to be mindful of the central 3-mm zone of these corneas. “You want that zone as normal as possible. You need to control the astigmatism and irregular topography in that central zone to get quality vision,” he said.

Case 2 highlighted that surgeons can use a small-aperture IOL in eyes with more astigmatism. However, patients may complain of quality issues if the central astigmatism is not controlled.

Another important point is that the carbon nanoparticle ring in the small-aperture device has a specific diameter, and if the pupil dilates beyond that diameter at night, the patient will have a lot of glare. Therefore, the pupil size in low-light conditions, in other words, not exceeding 5 mm, is a consideration when choosing patients.