Steps to success in implanting toric IOLs

This strategy before, during and after surgery can improve patient outcomes.

By James A. Davidson, MD, FACS

About the Author
	James Davison, MD, is board chairman of the Wolfe Eye Clinic in Marshalltown, Iowa where he specializes in cataract and refractive surgery. He can be reached at jdavison@wolfe clinic.com. Disclosure: Dr. Davison is a speaker for and consultant to Alcon.

Historically, performing cataract surgery for patients with severe astigmatism has presented challenges. The advent of the high-powered toric IOL has given surgeons the tools to address the needs of these patients. However, toric IOLs have ushered in a host of new challenges. Even slight off-axis alignment, for example, can lead to under or overcorrection and, ultimately, unsatisfied patients. So technical proficiency and surgical precision is vital to achieving optimal outcomes. To achieve these desired results, physicians need strong patient education skills as well as surgical finesse and the strategy to head-off complications before they develop.

This article will review techniques surgeons can use to achieve the best outcomes and most satisfied patients with toric IOL technology. This approach takes into account preoperative measurement, patient eligibility and selection, surgical execution and postoperative assessment.

PREOPERATIVE MEASUREMENTS

Initial testing

Cataract patients go through a number of tests and measurements. The key determinants of IOL selection are manifest refraction, automated keratometry and axial length measurement. For spherical power selection, our office uses the IOLMaster (Carl Zeiss-Meditec, Dublin, Calif.). If the formulas present a non-agreement of 0.50 D, we take the lower power recommended between the Haigis and SRK/T formulas.

Figure 1: Pentacam images show differences in total corneal refractive power vs. anterior corneal power, which dictate toric IOL selections. A) OD 43.40 43.90 @171=0.5 D; B) OD 43.70 44.70 @089=1.0 D; C) OS 44.00 45.20 @6.1=1.2 D; D) OS 43.20 44.90 @00.1=1.7D.

If the variation is as high as 1.00 D, we split the powers. For any greater variations, our office applies the Holladay II formula as a tiebreaker. The axial lengths and keratometry should make sense within clinical context; that is, an axial length variation of 1 mm should usually result in a corresponding refractive variation of about 3.00 D and the signal-to-noise ratio must be 100 or greater or immersion ultrasound should be used.

For toric IOL consideration, we use the total corneal refractive power as determined by the Pentacam (Oculus Inc., Arlington, Wash.). This takes into account the contribution of both anterior and posterior corneal surfaces and helps prevent overcorrection of with-the-rule astigmatism and undercorrection of against-the-rule astigmatism, which can occur when only the anterior surface is used for input into the toric IOL calculation (Figure 1).¹

Figure 2: The monitor displays the NextGen IOL calculation page.

To reduce waiting time and improve flow through the clinic, I order Pentacam corneal analysis on all cataract evaluations as a standard part of preoperative testing. This is one of the first tests we perform to help ensure the cornea is ready for surgery. This test is non-reimbursable, but is necessary to determine which patients might be good candidates for toric IOLs and what astigmatic corrections could be applied.

Review the findings

All collected diagnostic data is automatically entered into the EHR and is displayed on a monitor during the examination (Figure 2). The physician enters details of the exam into the system in real time. This makes it easy to review findings with patients. Together, patients and physicians can discuss options and create and enter plans into the EHR.

This planning includes IOL selection using the Alcon Toric IOL Calculator (Alcon, Fort Worth, Texas) for Alcon IOLs with the designation of 0.25 D average surgically induced astigmatism (SIA) created by a 2.4-mm primary incision. My personalized SIA was derived from my own data, using an IOL calculator Warren Hill, MD, had created (www.doctor-hill.com). The Alpins Statistical System for Ophthalmic Refractive Surgery Techniques (ASSORT) that Noel Alpins, MD, developed (www.assort.com) offers increased sophistication for pre- and postoperative toric IOL analysis and planning.

Figure 3: Corneal ABM dystrophy creates irregular astigmatism not amenable to toric IOL application.

PATIENT ELIGIBILITY AND SELECTION

Managing expectations

A patient’s desire to have toric IOLs implanted and his or her understanding of the goals of the procedure are among the first, and perhaps most important, determinations to make during the evaluation. Our patients receive an introductory letter urging them to consider options that may include femtosecond laser surgery and toric or multifocal IOLs. The letter includes costs of these options so patients have ample time to consider them. If they don’t recall the letter, we give them another copy and ask them to read it prior to testing.

Refractive cylinder

The preoperative discussion includes an explanation of refractive cylinder, its impact on uncorrected vision, and its incorporation into glasses or contacts. Sometimes, we need to detail and distinguish both keratometric and lenticular astigmatism and the way both contribute to refractive cylinder. This is especially important if the two astigmatic components have cancelled each other in the preoperative state as that would leave the patient exposed to uncompensated corneal astigmatism after surgery using a non-toric IOL.

LASIK options

We then tell patients the measurements and formulas have limits of accuracy. We explain it is similar to throwing darts at a dartboard. Statistically, the chances to get close to our goal are good, but due to factors such as scatter, it’s rare to “throw a bulls eye” for both cylinder and spherical components.

We explain the procedure does not have the predictability of LASIK and that, if they’re looking for that level of predictability, we could offer a discounted LASIK procedure following cataract surgery. The surgical scheduling nurse adds these details to the patient’s informed consent document.

Figure 4: We perform limbal marking when the patient is seated.

Getting predictable results

Regular and symmetrical corneal astigmatism will yield the most predictable results. Together, the patient and doctor must determine what qualifies as technical success and outcome satisfaction for patients with minimal to moderate irregularity or asymmetry and those with corneal abnormalities, such as anterior basement membrane dystrophy or previous keratore-fractive surgery (Figure 3). Toric IOLs can be effective in appropriately selected situations, but be sure to provide admonitions about the chances for complete success and satisfaction.

Patients with high amounts of astigmatism receive the best net reduction in cylinder even if axes are flipped,² but 0.75 D astigmatism can be addressed by 1.00 D toric IOL correction as well. This could result in less net cylinder (0.25 vs. 0.75 D) but an axis, which may be flipped 90°. Patients are affected more by cylinder amount than a change in direction. Cylinder as little as 0.50 D can reduce both visual acuity and low contrast acuity.³

Figure 5: A) The circular marker is centralized on the limbus then the inked axis marker creates and impression localizing the axis of placement; B) An inked Weck-Cel sponge reinforces the axis marks; C) The 2.4-mm keratome creates the primary incision while the eye is stabilized with the 22.5° paracentesis blade.

INTRAOPERATIVE STEPS

Markings

At surgery we mark the 6 o’clock limbus with a fine tip-marking pen with the patient in a seated position just before surgery (Figure 4). In the OR, we use a standard orientation marker to find and mark the correct axis (Figure 5). If the hand position feels awkward, use an inked Lester Hook to make discreet marks (Figure 6).

Figure 6: Use a Lester Hook to create discreet ink marks in awkward hand position situations.

We reinforce the marks with an inked Weck-Cel sponge (Beaver Visitec, Walthan, Mass.) so they do not fade. We orient the IOL dots at the center of the relatively wide sponge mark and make the 2.4-mm primary incision at 17° in the left eye and 190° in the right. Moving incisions to steep axes makes surgery more difficult and introduces unnecessary variables.

The capsulorhexis

We try to create 5-mm diameter capsulorhexis unless the patient is highly myopic. For highly myopic patients, we try to create a 4.6-mm capsulorhexis (most consistently accomplished using a femtosecond laser). With a 4.6-mm capsulorhexis, the capsule remnant can better grasp the IOL during the immediate postoperative period, especially if the IOL is placed relatively vertically (Figure 7). This helps prevent the IOL from falling off the axis and rotating to a horizontal position, which more often happens in large eyes.⁴

Figure 7: The three positioning dots on the anterior surface of the Alcon single-piece toric IOL optic are 0.20, 0.45 and 0.70 mm. from the optic edge (personal communication, Alcon Surgical 2009). The SNIT capsule/optic overlap estimate for this 4.6 mm diameter FLC created rhexis would be 7,7,6,6

We also try to extend the primary incision slightly more centrally in high myopes to avoid overinflation of those globes. Of course, IOLs need to be oriented properly and virtually all viscoelastic must be removed from in front of and behind the optic.

Preliminary positioning

I accomplish preliminary positioning with the I/A tip just 10° shy of the desired orientation. We then make the final adjustment with a 30-gauge cannula on a BSS syringe (Figure 8). We cannot be happy if orientation is not perfect and may have to go back to the silicone I/A tip to apply suction to the anterior IOL optic, then rotate it again if we initially miss perfection.

Figure 8: A 30-gauge cannula on a syringe accomplishes final positioning.

POSTOPERATIVE CONSIDERATIONS

Measure twice

If results are not acceptable for spherical equivalent or cylinder, consider greater use of spectacle correction, remeasurement and consideration of empirical power or astigmatism adjustments for the second eye, or reorientation if the IOL is off more than 10°. The Web site www.astigmatismfix.com created by John Berdahl, MD, and Dave Hardten, MD, can aid in calculations.

The future

New technologies are ever emerging to help better align toric IOLs. Preoperative registration systems help to align the intraoperative toric steep meridian to preoperative landmarks. Self-directed iris fingerprinting and automated limbal registration systems are features several manufacturers are developing. The Verion system from Alcon should electronically transfer preoperative data and images to the femtosecond laser and then to the surgical microscope display to better achieve good and consistent alignment and overall results.

These future technologies will help to communicate with patients, determine more accurate measurements, and gain a better view into individual patient’s pathologies. But the principles will remain the same. Complications associated with IOLs can be avoided by properly choosing patients, careful measurements, skillful surgical handling and strategic foresight. OM

References:

1. Koch DD, Ali SF, Weikert MP, Shirayama M, et al. Contribution of posterior corneal astigmatism to total corneal astigmatism. J Cataract Refract Surg. 2012;38:2080-2087.

2. Hoffmann PC, Auel S, Hutz WW. Results of higher power toric intraocular lens implantation. J Cataract Refract Surg. 2011;37:1411-1418.

3. Watanabe K, Negishi K, Kawai M, et al. Effect of experimentally induced astigmatism on functional, conventional, and low-contrast visual acuity. J Refract Surg. 2013;29:19-24

4. Davison JA, Weinstein AJ. Three strategies for reorienting AcrySof Toric lOLs. Cataract & Refract Surgery Today 2010 Mar:1-4.