The toric intraocular lens (IOL) provides a greater range, enhanced efficacy, more precise visual recovery for the cataract patient, and reduced potential of complications in a single surgery. Also, toric lenses provide the opportunity for optometrists to co-manage the patient’s recovery.
When we talk about premium intraocular lens (IOL) implants, our thoughts go straight to those cool presbyopic correcting lenses. However, another lens can provide as much refractive liberation and overall improved visual quality-the toric IOL.
Historically, toric IOLs were limited to a small subset of the patient population. Patients choosing the toric IOL paid a premium price. Because the lens was not custom lathed, the parameters were restricted and provided only a small amount of correction. Ironically, although there was a reduction in the magnitude of correction, most patients were still left with residual astigmatism, and therefore left feeling underwhelmed.
That was then. This is now. The toric IOL is a formidable option for our cataract astigmatic patient. Today’s toric lens provides greater range, enhanced efficacy, more precise visual recovery for the cataract patient, and reduced potential of complications in a single surgery.
The femtosecond laser has changed the landscape for patients by providing in-vivo astigmatic laser correction for astigmatism. Because there are limitations since the laser acts on the corneal surface, the magnitude of the astigmatism, and-even more important-the patient’s desire to have laser cataract surgery need to be factored. The same procedure can be accomplished with a blade-astigmatic keratometry-yet the limitations are similar to those of laser. Lastly, patients could opt to correct the astigmatism with a corneal refractive procedure, either LASIK or an Epi-LASIK, following lens implantation. Although this can lead to a more precise correction, the added cost, longer healing time, and the relative candidacy for corneal refractive surgery may be deterrents.
There are currently only two toric IOL options, the Elastic (STAAR Surgical) and AcrySof IQ (Alcon). Although both lens options provide some form of toric correction, there are differences between the lenses that some surgeons feel may benefit specific patients.
STAAR was the first company to bring toric technology to market in 1998. Its first lens was 10.5 mm in length and had small fenestrations on the haptics. The lens tended to rotate in the bag, thereby mitigating the toric correction. Theoretical calculations show that approximately one-third of the correction is lost if the lens is rotated 10 degrees off axis. Two-thirds of the effect is lost with 20 degrees of rotation, and a net increase in astigmatism will result if the lens is rotated more than 30 degrees off axis. In addition to proper surgical alignment, early and late rotational stability of toric IOLs is important. With this in mind, STAAR added a lens with larger fenestrations to adhere to the capsular bag. The STAAR silicone toric IOL is now manufactured in two astigmatic powers and two lengths. The 3.50 D power corrects approximately 2.30 D of astigmatism at the spectacle plane, while the 2.00 D power corrects approximately 1.40 D at the spectacle plane.
The AcrySof IQ, FDA-approved in 2005, is aspheric in design, built on soft acrylic material, and has a larger compliment of astigmatic options. Its single piece platform affords the surgeon a spectrum of astigmatic choices with six lens options that start at 1.50 D to 6.00 D in 0.75 D steps. This translates to corneal astigmatism correction of 0.75 D to 4.11 D. In clinical trials, this lens had a mean rotation of less than 4 degrees and no lenses had a rotation greater than 15 degrees at 6 months.
The toric IOL is an exceptional opportunity for cataract patients with corneal astigmatism. Moreover, the toric lens is a complement for patients who previously had corneal refractive surgery or corneal degenerations, such as keratoconus. By making a significant reduction in the cylinder power, an AK or LASIK could still be accomplished to provide uncorrected best vision.
Post-operative treatment of patients with toric IOLs is consistent with care for patients who have a standard lens, except for the potential rotation of the lens. Although lens rotation is unlikely, circumstances exist that may cause the lens to rotate. At the 1-week to 1-month follow-up visit, it is important to ensure that best corrected acuity is achievable.
Because varying degrees of misalignment can decrease visual acuity, the sooner the lens is realigned, the patient will have a better chance to regain vision. Therefore, it is important to know the axis the surgeon has aligned the lens in the bag because this may vary from the patient’s keratometric astigmatism axis. Dilation will be necessary to look for the lens markings in that meridian to properly assess the orientation.
Cataract surgery is an opportunity for patients to achieve excellent uncorrected visual acuity. Patients with corneal astigmatism should not be left on the sidelines. The toric IOL can help make optimal vision a reality in a safe and efficacious manner.ODT