Validating long-term toric IOL performance

Take-home: Five years of experience with the Rayner T-flex aspheric IOL show it to be a safe, highly effective long-term method of correcting the widest possible range of sphere and cylinder errors in pseudophakic patients with pre-existing corneal astigmatism. 

There have been numerous studies of the short-term results (up to 1 year) with toric IOLs, with a general consensus that they are an effective tool for managing astigmatism in cataract-surgery patients. But what about performance over the longer term – say, past 5 years?

To answer this question, we conducted a retrospective analysis including 507 eyes of 417 patients presenting for cataract surgery over a 5-year period (from August 2007 to August 2012). This was a single-surgeon, single-centre study utilising the T-flex IOL (Rayner Intraocular Lenses, Hove, UK). We included all comers: patients with primary and secondary astigmatism, post-refractive surgery, penetrating keratoplasty, keratoconus and corneal scarring. However, to be eligible for inclusion, patients had to have a corneal astigmatism of +0.7 D or greater at the corneal plane (approximately +1.0 D at the IOL plane).

A single surgical technique was used throughout the study. After administering a topical anaesthetic, with the patient seated upright, I first marked the cardinal axis to avoid cyclo-torsion. Then, when the patient was in a supine position, I marked the steep axis with 

which the toric IOL is aligned. Finally, I marked the capsulorhexis. This is because a well-centred capsulorhexis is very important to ensure a uniform 360° overlap that will maximise the rotational stability of the lens and provide consistent effective lens position. I performed bimanual surgery with vertical phaco chop to remove the nucleus and then implanted the lens using a Rayner soft-tipped injector through a clear corneal incision that was initially 2.8 mm but later 2.4 mm. The lens was placed in the capsular bag then the viscoelastic was removed from behind the lens.

Analysis

Analysis of sphere correction

An analysis of sphere correction showed that, preoperatively, the sphere ranged from –10.5 to +9.0 D and axial length from 20.99 to 27.75 mm. However, the postoperative mean absolute error was 0.35 D and the standard deviation was 0.46 D (Figure 1). With regards to cylinder correction, preoperative refractive astigmatism ranged from 0.0 to 7.25 D and keratometric astigmatism from 0.67 to 7.86 D. Additionally, keratometric values ranged from 33.35 to 59.00 D and IOL toricity from 1.0 to 11.0 D. Postoperatively, mean cylinder was 0.26 D with a standard deviation of 0.35 D, and 90% of patients had 0.5 D or less of astigmatism. Stratifying the results according to with-the-rule and against-the-rule astigmatism revealed that with-the-rule cases generally did better than those patients with against-the-rule astigmatism.

Overall, 23 patients had 1.0 D, seven patients had more than 1.0 D and no patient had more than 2.0 D of residual astigmatism. Interestingly, the seven patients with more than 1.0 D of residual astigmatism all had primary astigmatism. However, they all had less astigmatism postoperatively, indicating that in a small percentage of patients there are factors other than anterior corneal curvature contributing to total ocular astigmatism.

Very few complications were noted in this 507-eye study. Specifically, two patients had radial tears in the continuous curvilinear capsulorhexis, but we were still able to implant the T-flex in the capsular bag without any problems. The rate of cystoid macular oedema was 1%; all cases were resolved with topical steroids and ketorolac treatment. There were no patient returns to theatre to re-rotate misaligned lenses.

Tips and considerations 

 Tips and considerations

It has been established that biometry is the cornerstone of good outcomes following implantation of a toric IOL. Indeed, the single biggest source of error in refractive outcomes following toric lens implantation is inaccurate biometry. When a cataract patient presents at my centre, keratometry is one of the first tests I perform. However, it is important to remember that keratometry measures reflection from the tear film and not the curvature of the cornea. If a surgeon overlooks this simple but vital point, their patients’ refractive outcomes will likely be doomed from the outset. Although Rayner helpfully provides the Raytrace system, a quick and easy to use online IOL power calculator, I prefer Dr Jack Holladay’s program. This is because it allows me to import data electronically from the IOL Master (Carl Zeiss Meditec) that I use for keratometry (both calculating the axis of astigmatism and the power of correction required), thus eliminating the possibility of transcription errors.

Another important point is to ensure the A-constant values are continually optimised – in my case, the A-constant was optimised/personalised at 118.7. Dr Holladay’s program also provides a chart that gives the degree of toricity recommended for any given spherical power.

A final issue worth addressing here is a fear experienced by many cataract and refractive surgeons – that of IOL misalignment. Reassuringly, however, a paper published by Noel Alpins in the Journal of Cataract and Refractive Surgery in 1997 demonstrated that only about 5% of toric power is lost with a misaligned lens as long as the lens placement is within 10 degrees of intended axis.⁵

Overall, findings from our 5-year “audit” of the Rayner T-flex aspheric lens show that it is a safe, highly effective long-term method of correcting the widest possible range of sphere and cylinder errors in pseudophakic patients with pre-existing corneal astigmatism.

The T-flex solution

The T-flex solution

There are a number of toric IOL options, with variations in material type, design, diameter, incision size and spherical /cylindrical power. In my practice, I regularly use the T-flex aspheric IOL (Rayner Intraocular Lenses Limited, Hove, UK), which offers a precise superior alternative to incisional methods for the treatment of pre-existing corneal astigmatism.³ Available in cylinders 1.0 to 11.0 D, and from –10 to +35.0 D for spheres (subject to spherical equivalent), the T-flex IOLs offer a far greater range of cylinder and sphere combinations than most other toric IOLs, thus allowing the correction of significant levels of astigmatism. Typically, once we cross the +1.5 D threshold, many other toric lenses on the market are available in 0.75 D or 1.0 D steps for toricity. The Rayner lens is special because it comes in 0.50 D steps, therefore giving us much more flexibility in treating our astigmatic patients. Additionally, the T-flex incorporates Anti-Vaulting Haptic Technology, which progressively takes up forces generated within the contracting capsular bag, thus maintaining excellent centrational and rotational stability.⁴

Daniel A. Black, MBBS (Qld) FRANZCO FRACS A/FACAsM

E: daniel.black@suneye.com.au

Daniel A. Black is an ophthalmologist in practice at the Sunshine Eye Clinic in Birtinya, Queensland, and a Senior Lecturer at the University of Queensland, Australia. Dr Black states that he has no financial interests in Rayner Intraocular Lenses Ltd.

References

1. Visser N, Bauer NJ and Nuijts RM. J. Cataract. Refract. Surg. 2013; 39: 624-637.

2. Saragoussi JJ. J. Fr. Ophtalmol. 2012; 35(7): 539-545.

3. Rayner. http://www.rayner.com/t-flex. Last accessed 1 September 2014.

4. Claoué C. Clin. Surg. Ophthalmol. 2008; 26(6): 198-200.

5. Alpins NA. Cataract Refract. Surg. 1997; 23(10): 1503-1514.