Many cataract patients with preexisting astigmatism can benefit from implantation of a toric IOL. Less than 1%, however, present with more than 5.00 D of astigmatism, which exceeds the corrective capabilities of standard toric IOLs.1In these circumstances, combining implantation with limbal relaxing incisions or LASIK can achieve higher levels of correction. Unfortunately combination strategies can be complex and unpredictable, and patients may have to undergo additional postoperative adjustments.
WHEN ONE SIZE DOES NOT FIT ALL
Recently, several IOL manufacturers have begun to offer a line of customized toric IOLs to provide higher levels of cylindrical correction—up to 11.00 or 12.00 D. The MicroSil (HumanOptics AG) and the Lentis TPlus (Oculentis GmbH) are available in increments of 1.00 and 0.75 D, respectively, and the T-flex (Rayner Intraocular Lenses Ltd.) is available in increments of 0.25 D. The latter also provides spherical correction from -10.00 to 35.00 D and minimizes induced higher-order aberrations (HOAs). 2 It can be implanted through a 2.8-mm incision.
As illustrated by the following case studies, customized aspheric toric IOLs can be implanted to achieve refractive correction and excellent visual quality even in challenging patients for whom standard toric IOLs and incisional methods of astigmatism correction, alone or in combination, might not work.
Case Study No. 1: Mixed astigmatism. A 39-year-old woman presented with mixed astigmatism (Figure 1A). A preoperative refraction of +4.50 -10.00 X 178° yielded 0.8 BCVA in both eyes. She was unable to maintain employment because she was contact lens intolerant and her astigmatism was too high for spectacle correction. Three months after cataract surgery and implantation of T-flex 573T aspheric toric IOLs (Figure 1B) bilaterally, the refraction in her left and right eyes was +0.25 -0.75 X 103°, yielding 0.8 BCVA, and +0.75 -1.75 X 109°, yielding 1.0 BCVA, respectively. The IOL was positioned at an axis of 92° (target axis, 90°) in the left eye and at an axis of 95° (target axis, 95˚) in the right.
Case Study No. 2: Pellucid marginal degeneration (PMD). A 60-year-old woman presented with PMD and subcapsular cataracts. Preoperative refraction in her right eye was -12.00 -7.00 X 111°, yielding 0.4 BCVA, with an anterior chamber depth (ACD) of 4.3 mm and pachymetry of 529 μm (Figure 2A). In her left eye, preoperative refraction was -8.75 -6.25 X 64°, yielding 0.4 BCVA, ACD was 4.4 mm, and pachymetry was 493 μm. Three months after cataract surgery with implantation of customized toric T-flex 573T IOLs, the refraction was +1.50 -2.25 X 158°, yielding 0.9 BCVA, and 0.00 -1.50 X 80°, yielding 1.0 BCVA, in her right and left eyes, respectively. The IOL was positioned at an axis of 165° in her right eye (Figure 2B) and 40° in her left. Her right eye had a residual cylindrical error of 2.25 D, but because the astigmatism had been reduced she was able to wear glasses to optimize vision.
Case Study No. 3: Shallow anterior chamber. A 28-year-old woman presented with acute glaucoma secondary to anterior chamber crowding in her right eye (Figure 3). Examination revealed shallow anterior chambers (right eye, 1.59 mm ACD; left eye, 1.71 mm ACD), thick natural lenses in both eyes, and axial lengths of 21.9 mm in the right eye and 22.2 mm in the left. Treatment with acetazolamide and dorzolamide reduced her intraocular pressure (IOP) from 50 to 12 mm Hg. To create more space, relieve the crowding in the anterior chamber, and prevent future elevated IOP, she underwent cataract surgery in her right eye. Implanting a T-flex 573T IOL also corrected her high astigmatism and improved her refraction from -5.00 -6.00 X 180°, yielding 0.4 BCVA preoperatively, to -0.75 -2.25 X 105°, yielding 0.8 BCVA at 3 months postoperative.
THE FEATURES THAT MATTER
The C-haptic design of the T-flex, featuring antivaulting haptic technology, provides excellent rotational stability. This is especially important in eyes with large cylindrical errors, as small deviations from the target axis can significantly affect the final refractive result. In a study of 33 eyes implanted with the T-flex (623T), less than 10% had IOL rotation of 10˚ or more. 3
The T-flex also has an enhanced square-edge design to prevent cell migration and lower the risk of posterior capsular opacification.
WHAT’S NEXT FOR TORIC IOLS?
As manufacturers work on developing an effective accommodating toric IOL, we should not lose sight of the promising solutions that are already available. Customizable toric IOLs offer an effective and surgeonfriendly solution for the challenging task of treating highly astigmatic patients.
Rudy M.M.A. Nuijts, MD, PhD, is a Professor of Ophthalmology in the Department of Ophthalmology at the Academic Hospital Maastricht, Netherlands. He is a member of the CRST Europe Editorial Board. Dr. Nuijts states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +31 43 3877343; email@example.com.
- Ferrer-Blasco T, Montés-Micó R, Peixoto-de-Matos SC, et al. Prevalence of corneal astigmatism before cataract surgery. J Cataract Refract Surg. 2009;35:70-75.
- Company data. Available at www.rayner.com.
- Entabi M, Harman F, Lee N, Bloom PA. Injectable 1-piece hydrophilic acrylic toric intraocular lens for cataract surgery: Efficacy and stability. J Cataract Refract Surg. 2011;37(2):235-240.