Introduction

In November 1998, the Staar (Monrovia, Calif) plate haptic toric IOL became the first toric lens approved by the U.S. Food and Drug Administration. Earlier and concurrent studies have suggested that the plate haptic design is superior to that of curved haptic designs in terms of long-term rotational stability.1,2 Using serial digital photographs, Patel demonstrated that late postoperative rotation was unusual with plate haptic lenses, but more frequent with 3-piece designs. However, Patel's study also confirmed that both lens designs can rotate during the immediate postoperative period; the plate haptic design rotated more frequently.2 Presumably, it is not until the capsular bag contracts that the corners of the plate haptic IOL are able to resist natural rotational forces. Patel’s study used a 10.5-mm plate haptic IOL, which is shorter than the two toric IOL sizes (10.8 mm and 11.2 mm) available from Staar.

I have found corneal limbal relaxing incisions (LRIs) to be effective in reducing low amounts of astigmatism (less than 2 D). I use a preset, 600-mm blade and the Gills nomogram. Although this method does not adjust for individual variation in peripheral corneal thickness and corneal diameter, the dominant variable is the patient’s age. As with all incisional keratotomy, increasing age amplifies the effect of a given incision length. In addition, the greater the amount of targeted astigmatism effect, the more variable and unpredictable are the results of LRIs.

Toric IOL Indications and Specifications

For these reasons, I have found the toric IOL to be particularly appropriate for two types of patients. The first indication is cataract patients younger than 65 years with 2 D or more of astigmatism, but whose age significantly reduces the attainable effect from incisional keratotomy. The second group consists of patients with the largest degrees of astigmatism (e.g., more than 3 D). In addition to more unpredictability, against-the-rule astigmatism in these patients requires combining the temporal clear corneal incision with a temporal LRI. Slight override of the incision edges can cause significant discomfort and foreign body sensation for these patients.

The Staar toric plate haptic IOL has large haptic fenestrations, and is available in two astigmatic powers and two lengths. The 2-D toric IOL corrects approximately 1.50 D of keratometric astigmatism, whereas the 3.5-D toric IOL corrects approximately 2.25 D. The Staar "TF" lens was the original FDA-studied design. It has an overall length of 10.8 mm. Subsequently, Staar released the longer, 11.2 mm "TL" model for spherical powers of less than 23.5 D. The haptics of the longer lens have a matte finish to make them less slippery.

Slide 1A

Slide 1A
Slide 1B

Slide 1B

The spherical power of the toric IOL is calculated in the same way as for a conventional IOL. Next, the astigmatic power is selected without having to adjust the spherical power. Hash marks on the IOL allow this cylindrical power to be surgically aligned with the steeper "plus" axis of astigmatism (Slide 1A and Slide1B). To avoid any potential influence of lenticular astigmatism, one should use the keratometric reading, rather than the refraction, for selecting the IOL toric power and axis. Rigid contact lens wear should be discontinued for 1 week to obtain more accurate keratometric readings. These patients should be informed that any residual postoperative astigmatism can be corrected only with spectacles or a toric soft contact lens.

Slide 2

Slide 2
Slide 3

Slide 3

Misalignment of the toric IOL axis reduces the amount of astigmatism correction. With 10° of axis deviation, one-third of the effect is lost. With 20° of axis deviation, two-thirds of the effect is lost. Lens misalignment of more than 30° produces a net increase in astigmatism (Slide 2). In the FDA study data, 24% of the toric IOLs ended up more than 10° off axis (12% were more than 20° off, 8% were more than 30° degrees off, and 5% were more than 45° degrees off axis) (Slide 3). The FDA studied the shorter 10.8 mm toric size.

So far, significant late rotation of the lenses has not been reported, consistent with the published Patel findings.3 Thus, the key to success with the toric IOL is in avoiding early postoperative rotation of the lens. This depends on having an adequately long IOL for the patient’s capsular bag diameter. The learning curve for my first 40 cases underscores this point.

Personal Learning Curve (50 Cases)

In February 1999, I implanted my first six TF (10.8 mm) toric IOLs in four patients. The longer TL (11.2 mm) lens had not yet been announced or released. I used Viscoat (chondroitin sulfate, sodium hyaluronate, Alcon) in these uncomplicated cases under topical anesthesia, and proper IOL orientation was confirmed each time by the operative video. In three eyes, the axis remained within 15° of the targeted axis postoperatively. However, one patient had misalignments of 70° and 85° in each eye by the first postoperative day. Each time, the IOL was immediately repositioned because the doubling of her astigmatism was intolerable. Both lenses have remained perfectly aligned since then.

A third IOL was 30° misaligned by postoperative day 1 and I waited the recommended 2 weeks to surgically realign the lens. During surgery, I discovered that the anterior capsule was already fibrotic and the anterior and posterior capsules had already fused peripheral to the IOL. Use of a spatula and viscodissection were required to reopen the capsular bag so that the IOL could be rotated. The lens did not move easily, but proper and stable alignment was eventually achieved.

Staar made the first TL lenses approved in the United States available to me in March 1999. I used only the TL IOLs in the next 44 consecutive cases, and none has required repositioning. All of the toric IOLs used had 3.5 D toric power.

Current Technique and Results

My current technique employs the following guidelines:

Slide 4A

Slide 4A
Slide 4B

Slide 4B

I implant the toric IOL under topical anesthesia without postoperative patching or shields. With the patient sitting upright on the operating table just before surgery, the 6 o’clock limbus is marked with a pen. Once under the microscope, a Mendez-style degree gauge is then used to orient two limbal ink marks that identify the desired axis. Later, the IOL axis marks can be aligned with these ink marks and double checked against the preoperative notes or chart.

Preoperatively, I inform patients of the potential need for surgical repositioning, and postoperatively, I perform a dilated exam on postoperative days 1 and 6 to check the IOL axis. Any rotation tends to occur between the time of surgery and the first postoperative morning. I have yet to record any significant change from the axis on postoperative day 1. Based on my experience with three badly misaligned cases, I would perform repositioning by 1 week or earlier. Once the capsular bag fully contracts (e.g., by 2 weeks with my third case), more force is required to rotate the IOL, and this may increase the chance of tearing the capsular bag.

Slide 4C

Slide 4C
Slide 4D

Slide 4D

Excellent rotational stability was achieved with this technique in my series of 44 consecutive TL (11.2 mm) toric implants: 68% were within 5° of target axis; 91% were within 10° of target axis; and 98% were within 15° of target axis. My repositioning rate was 0% with the longer TL IOL compared with 50% with the shorter TF IOL (three of six cases).



Slide 4E

Slide 4E
Slide 4F

Slide 4F
Slide 4G

Slide 4G

Conclusion

Toric IOLs are an excellent complement to corneal astigmatic incisions. They are helpful in those cases where LRIs are not powerful or predictable enough. Proper IOL sizing is critical for initial rotational stability. Until the capsular bag begins to contract within the first day or so, a plate haptic IOL that is too small for the bag can rotate. With the availability of the longer 11.2 mm model, toric IOLs have become a valuable addition to my practice.

Video

Video

References

  1. Shimizu K, Misawa A, Suzuki Y. Toric intraocular lenses: Correcting astigmatism while controlling axis shift. J Cataract Refract Surg. 1994;20:523-526.
  2. Patel CK, Ormonde S, Rosen PH, Bron AJ. Postoperative intraocular lens rotation: A randomized comparison of plate and loop haptic implants. Ophthalmology. 1999;106:2190-2196.
  3. Ruhswurm I, et al. Astigmatism correction with foldable toric intraocular lens in cataract patients. J Cataract Refract Surg. 2000;26:1022-1027.

Dr. Chang has no financial interest in any of the products mentioned. This article was published as a video report on the British Journal of Ophthalmology Web site: Chang DF. Pearls on implanting the Staar toric IOL. Video report. Br J Ophthalmol. 2001;85(Jan).