Collaborative Case #008: IOL Selection Challenge

The patient has a number of IOL options, all of which can provide reasonably good visual outcomes. These include a monofocal IOL, a monofocal toric IOL, light adjustable IOL, or the IC-8 Apthera small aperture IOL. The one option that should be avoided is a range of vision IOL, such as a trifocal, multifocal or extended depth of focus IOL, as the irregular astigmatism will significantly reduce the quality of vision.

On discussion with the patient, she was interested in achieving the best vision possible. We discussed that a monofocal toric lens is a good option, as it can potentially correct the approximately 2.00 D of corneal astigmatism. However, IOL calculations can be a challenge. There are a number of formulas that can be used, including the Barrett Universal formula, Hill formula, and Kane formula. Although there are formulas developed for post-LASIK, post-RK, and keratoconus, there are no specific formulas developed for patients who have corneal scars causing irregular astigmatism.

Another challenge was discovered on additional testing. Two measurements were performed to determine the magnitude and axis of astigmatism. The topography (performed using an Oculus Pentacam [Oculus]) found 2.20 D of astigmatism, while biometry found only 1.55 D of corneal astigmatism (Figure 2). These measurements were repeated 3 weeks after ocular surface optimization with topical steroids and artificial tears, and the results were essentially unchanged.

Because there was a high likelihood of ending up over or undercorrected with a monofocal toric IOL (due to uncertainty around the IOL calculations), and because there would likely be some degree of residual astigmatism due to the differences in corneal astigmatism measurements, the patient requested an option with a greater chance of ending up with good uncorrected vision. The two options that can be considered in this case are the Apthera small aperture IOL and the Light Adjustable Lens. Both have their own advantages and disadvantages.

Apthera IOL

The Apthera small aperture IOL provides enhanced depth of focus. Because it is a small aperture and can also minimize the impact of corneal astigmatism on visual acuity. Therefore, even if the patient ends up a little ± 0.75 D) under or over-corrected on sphere, they should maintain good distance vision. The downside is that if they end up 1.00 D or worse off target, they would likely be disappointed with their visual outcome.

Light Adjustable Lens

This IOL can typically correct 2.00 D of both astigmatism and myopia/hyperopia. Because the Light Adjustable Lens can provide a reasonably good outcome, even if off-target due to uncertainty around the IOL calculations and corneal astigmatism measurements, the patient opted for this technology. She was also advised that she would need to wear UV-blocking glasses (provided by the company) until all light treatments were completed.

Cataract surgery was performed with placement of a Light Adjustable Lens, and the patient did well. Although adjustments can start as early as 3 weeks postoperatively, the patient ended up waiting until week 5 for her first light adjustment to confirm that the refractions were stable. At the 5-week examination, her UCVA was 20/40 OS. Refraction OS was: plano +1.25 x 055 = 20/25+. This refraction suggested that we would likely have been significantly off target with a toric IOL, as the axis shifted from about 078 on preoperative measurements to 055 at the 5-week examination. The patient also ended up with a spherical equivalent of +0.625, suggesting that she likely would have ended up off target on the sphere if she had opted for a monofocal IOL.

Following the first adjustment, the patient’s UCVA improved from 20/40 to 20/30+1, and her refraction improved from plano +1.25 x 055 to -0.25+0.75 x 084. Her BCVA remained stable at 20/25+ (Figure 3).

Although 20/30+1 UCVA was an excellent outcome, up to three light adjustments can be performed to further improve the vision. With that in mind, the patient returned for a second light adjustment, after which, her UCVA improved to 20/25+1 and the refraction improved to -0.50 + 0.50 x 070. Her BCVA was now able to reach 20/20- (Figure 4).

With this excellent result for a patient who had irregular astigmatism due to a mild superior corneal scar, the decision was made to lock in the Light Adjustable Lens, so that it will no longer change power. Four months after the lock-in light treatment (and 6 months postop), the patient returned. As expected, she maintained excellent UCVA. Her UCVA was measured at 20/25+1 and his refraction was -0.50 sphere, with BCVA of 20/20-1 (Figure 5).