Marking for Toric IOL Implantation

Save time in surgery with this preoperative step.

BY BYRON STRATAS, M.D.

When implanting a toric IOL, I have found that the practice of establishing landmarks at the preoperative visit using anterior stromal puncture (ASP) saves time in the OR. I mark the cornea on the steep axis within the central 6-mm zone using a Haag Streit BQ slit lamp (Wedel, Germany) and ASP (Figures 1 and 2).

Anterior stromal puncture (Figure 3) is an economical, accurate and efficient way to prepare to implant toric IOLs. It takes very little chair time at the preop consultation and requires no disruption of patient/surgeon flow on the day of surgery. We use a pre-formed, sterile, 25-gauge cystatome (BD Ophthalmic, Waltham, Mass.) (Figure 4). We are working on two variations of this marking technique with pre-loaded disposable instruments similar to those used to implant punctual plugs (and are seeking vendors for this also). One type will implant a microscopic, solid, foreign body, and the other will implant a small amount of corneal dye (tattoo).

The Preoperative Plan

During the surgery, I align the orientation marks on the cornea with those on the IOL.

A clear and detailed preoperative plan enables accurate intraoperative placement. My plan always includes the Alcon Toric Calculator (Fort Worth, Texas). The manual K's are given the highest weight and are compared to the other tests mentioned below.

First, the ocular surface is managed to address any surface irregularities from a tear dysfunction or anterior corneal disorder (e.g., Salzmann's nodular degeneration, epithelial basement membrane dystrophy, pterygium). Then I determine if the patient has regular or irregular astigmatism. Measurements are taken with an auto keratometer, the IOLMaster (Carl Zeiss Meditec, Dublin, Calif.), Pentacam (Oculus USA, Lynnwood, Wash.) or Magellan Mapper (Nidek, Fremont, Calif.), and a manual keratometer. Corneal spherical aberration has an important influence on my choice of treatment, especially when the cylinder is below 1.25 D.

Figure 1. Schematic depiction of IOL marks lined up with ASP marks in vivo.

A discussion helping patients identify their goals, needs and expectations is critical to success. Any patient with regular astigmatism can expect to see their uncorrected quality of vision improve when a toric lens is used. However, this lens does not correct both distance and near vision so the patient should be informed that glasses will be required for some activities.

Figure 2. The axis gauge on the Haag Streit slit lamp.

Choosing an IOL

The Acrysof SA60TT Toric IOL (Alcon) has set a new standard in toric IOL stability.¹ Now that the IOL will stay where we implant it, we need an accurate method to ensure proper orientation during surgery. Additionally, the platform of the Acrysof Toric IOL, based on a single-piece acrylic design, seems to have demonstrated little or no shift in effective lens position — which means the spherical component is also stable. The other style of toric IOL, the STAAR AA4203 Toric (Monrovia, Calif.), has been reported in the literature to have significant shifts in the spherical power due to shifts in the effective lens position as the capsule contracts.^2-6 The stability of both toric lenses in my hands far exceeds the stability of incisional keratotomy. The quality of vision when the correction is on the IOL may also exceed the quality of correcting it on the cornea, proving especially true once an aspheric toric IOL is available. Any patient who has 0.75 D or more of astigmatism causes me to pause and think through how and whether I can address it. For patients with less than 1 D of astigmatism who also demonstrate positive corneal spherical aberrations, I select a spherical aberration corrected IOL, such as the Acrysof SN60WF (Alcon), Tecnis Z9002 (Advanced Medical Optics [AMO], Santa Ana, Calif.), SofPort AO (Bausch & Lomb, Rochester, N.Y.) and Clariflex (AMO). Managing the spherical aberrations often negates the significance of the toricity. These patients seem to tolerate the cylinder better when their spherical aberrations are at or slightly below zero. It is important to note that both toric IOLs are currently on platforms that have been shown to exacerbate or at least not improve spherical aberrations. For patients with a diopter or more of regular corneal astigmatism, I use a toric IOL.

Figure 3. Anterior stromal puncture along the steep axis. I am now placing the ASP away from the limbus at the 6 mm to 7 mm central optical zone. This location does not cause optical symptoms, yet is quickly identified during cataract surgery.

Figure 4. A stiff (25-gauge) cystatome provides control with a guarded depth.

Efficient Surgery = Safer Surgery

The less time a surgery takes, the less exposure to potential complications. Along with recent trends in surgery toward minimally invasive procedures, preoperative steps have been developed to reduce surgical time. ASP before the implantation of toric IOLs is an efficient procedure that promotes accuracy and reduces surgical time. This is an advantage not only to the patient with astigmatism, who will run a lower risk of intra- and postoperative problems, but also to the ophthalmologist who wishes to maintain an efficient OR and clinic. The technology for toric IOL placement is available now to establish a high level of accuracy without comprimising efficiency. OM

References

1. Horn JD. Status of toric intraocular lenses. Curr Opin Ophthalmol. 2007;18:58-61.

2. Patel CK, Ormonde S, Rosen P, Bron AJ. Postoperative intraocular lens rotation; a randomized comparison of plate and loop haptic implants. Ophthalmology. 1999;106:2190-2196; discussion Apple DJ, 2196.

3. Shimizu K, Misawa A, Suzuki Y. Toric intraocular lenses: correcting astigmatism while controlling axis shift. J Cataract Refract Surg. 1994;20:523-526.

4. Strenn K, Menapace R, Vass C. Capsular bag shrinkage after implantation of an open-loop silicone lens and a poly(methylmethacrylate) capsule tension ring. J Cataract Refract Surg. 1997;23:1543-1547.

5. Vass C, Menapace R, Schmetterer K, et al. Prediction of pseudophakic capsular bag diameter based on biometric variables. J Cataract Refract Surg. 1999;25:1376-1381.

6. Vasavada A, Singh R. Relationship between lens and capsular bag size. J Cataract Refract Surg. 1998;24:547-551.

Byron Stratas, M.D., F.A.C.S., the founding medical director of the LASIK and Refractive Center at Eye Associates of Wilmington, Wilmington, N.C. His practice is limited to refractive and cataract surgery. He has no financial interest in any of the information contained in this article. Dr. Stratas can be reached at bstratas@wilmingtoneye.com.