Visual Acuity Outcomes of Toric Lens Implantation in Patients Undergoing Cataract Surgery at a Residency Training Program

Abstract

Ophthalmology residents must become competent in the use of a variety of intraocular lenses (IOLs) and refractive technologies designed to reduce spectacle use after cataract surgery. Our study of visual acuity outcomes with toric IOLs at the Harry S. Truman Memorial Veterans’ Hospital revealed that residents achieved an uncorrected visual acuity of 20/40 or better in 88% of the surgeries they performed, a rate comparable to that reported by other residency programs and by cataract surgeons.

Introduction

Cataract surgery offers a unique opportunity to improve vision in three ways: by exchanging a clouded, or opacified, lens with the replacement intraocular lens (IOL); by compensating for variability in size or shape of the patient’s eye with a specific power of correction in the IOL, and by making adjustments in the curvature of the cornea to correct astigmatism. In some individuals the cornea’s contribution to visual acuity is a regular spherical arc. However, in 22% to 28% of the population,¹ correction for astigmatism is also required when the cornea has more of a football shape, where the arc of curvature is steepest in one axis and shallowest in a perpendicular axis. Toric IOLs were introduced in 1998 to correct this issue and have steadily gained in popularity. The lenses themselves take a similar astigmatic shape and the ophthalmologist can use corneal topography to choose the appropriate lens and align the axis to maximize the patient’s visual improvement. These lenses and other so-called “premium” lenses are becoming more available to patients and knowledge of their use may be helpful to primary care physicians who find themselves in the position of counseling their patients about cataract surgery.

In addition to toric IOLs to correct for astigmatism, there are techniques such as limbal relaxing incisions (LRI) or similar cuts in the cornea, called astigmatic keratotomy (AK), which are designed to flatten the cornea at designated axes in order to try to correct for astigmatism. For appropriate patients, LASIK (laser-assisted in situ keratomileusis) or photorefractive keratectomy (PRK) may be an appropriate therapy for correcting astigmatism at the time of cataract surgery. While these options offer certain advantages, they also have drawbacks. The reliability and accuracy of LRI are dependent both on the skill of the surgeon and the healing properties of the tissue.² In addition, LASIK or PRK may be a cost barrier for some patients. By requiring a second procedure, each of these approaches introduces some amount of additional risk when added to cataract extraction and IOL placement. The toric lens offers the benefit of managing both cataract and astigmatism in a single effort.

Candidates for Toric Lenses to Correct Astigmatism

Generally, patients are considered to be good candidates for toric lenses if the preoperative evaluation highlights a mostly regular astigmatism that is expected to be visually significant in the postoperative course if a standard lens were implanted. Regularity of the astigmatism is defined as the presence of a single, definable axis of maximal and minimal arc along which a toric lens can be aligned. The level at which astigmatism becomes visually significant varies greatly among patients, but generally astigmatism less than 0.75D (diopters) is well tolerated by most patients. Many patients can tolerate 0.75D to 1.25D of astigmatism, whereas nearly all patients with uncorrected astigmatism greater than 1.25D experience visual deficit. Given these generalities, it is common practice to consider astigmatic correction for patients with greater than 1.0D of astigmatism.³

Toric lenses are only currently available in certain measurements so patients at the extremes of these values will not have satisfactory correction from the lens itself. In these cases, the addition of LRI is particularly useful. Most toric lenses will not correct presbyopia, thus patients will still require spectacles for reading. In the United States, there currently is one available accommodating toric lens (Trulign), but it is not approved for the correction of presbyopia. Multifocal toric lenses for the correction of both astigmatism and presbyopia are used internationally and await FDA approval for use in the United States.

Implantation of toric lenses adds a layer of complexity to surgical planning and is generally an increased cost compared to implantation of a standard IOL. Possible complications associated with toric lenses include incorrect lens selection from either incorrect measurement or calculations, improper lens placement from inaccurate surgical marking or implantation technique, and postoperative lens rotation resulting in inaccurate alignment.⁴ As toric and other premium lenses become more widely used, it is a clear necessity that ophthalmology residents become competent in their use. The faculty physicians at the Harry S. Truman Memorial Veterans’ Hospital (Truman VA Hospital), which is affiliated with the Department of Ophthalmology, Mason Eye Institute, at the University of Missouri, began working with both toric and presbyopia-correcting lenses several years ago for selected patients. In 2011, the Truman VA Hospital made toric lenses available to patients on a routine basis, leading to greater accessibility for patients and increased resident involvement in toric surgeries.

The standard preoperative evaluation for cataract surgery includes the measurements that identify candidates for toric IOLs. Important elements include the patient’s attitude towards the surgery and their ability to undergo the procedure. The patient’s visual acuity is assessed as well as the patient’s response to glare and dim environments, as necessary. The refraction can be helpful to determine how much of the patient’s visual impairment is from corneal aberration rather than cataract or retinal disease. The fundus of the eye is examined for evidence of macular disease that may limit the patient’s visual potential. If the decision is made to proceed with plans for cataract surgery, then corneal topography is performed as well as manual and automated measurements of axes of astigmatism and axial length of the eye. At this point these measurements are used to calculate the strength of the IOL and, if appropriate, to select the proper toric model.

Multiple studies have been conducted to explore the accuracy of toric placement. A meta-analysis reviewing 11 studies of toric IOL placement by experienced surgeons found a collective improvement in uncorrected distance visual acuity (UDVA) and spectacle independence from 40% of patients requiring eyeglasses all of the time to 0% requiring eyeglasses all of the time. Although not all studies reported data on preoperative refractions, 7 of the 11 study populations achieved a mean UDVA of 20/40 or better and 10 of the 11 study populations achieved UDVA of 20/50 or better. With toric lenses, the proportion of patients never requiring spectacles increased from 15% to 85%.⁵

Corneal astigmatism is common in patients who are candidates for cataract surgery and IOL implantation. A prevalence study, in Germany, which included over 23,000 eyes, found that approximately 8% of people have at least 2.00D of corneal astigmatism and that 16% of all eyes are candidates for toric lenses based on a 1.50D threshold.¹ In a study of more than 4,500 patients preparing for cataract surgery, 34.8% were found to have at least 1.00D of astigmatism and more than 20% were toric candidates.²

Methods

To get a measure of our institution’s competency in training ophthalmology residents to perform cataract surgery and toric lens implantation, we conducted a retrospective study of visual acuity outcomes of cataract surgery and toric lens implantation in patients undergoing cataract surgery during the early period in which toric lenses were offered at the Truman VA Hospital. We then compared the outcomes in our VA patients with those reported by other ophthalmology residency training programs and by experienced cataract surgeons. The study was approved by the Institutional Review Board of the University of Missouri and the Harry S. Truman Veteran’ Memorial Hospital, Columbia, Mo. Patients were seen at the Eye Clinic of the Truman VA Hospital from July 2011 to September 2012, during the first year in which toric lenses were made available to patients at the Truman VA Hospital. Patients who met inclusion criterion of at least 1.00D astigmatism were offered implantation of the toric lens. AcrySof SN6AT3-SN6AT9 toric lenses (Alcon) were used.

The study population was comprised of 32 men (48 eyes), aged 54–96 years. Patients were not excluded because of ocular comorbidities such as glaucoma, hypertensive retinopathy, macular degeneration, and corneal scarring, with the exception of one patient who was excluded because of hypotonous maculopathy following a glaucoma surgery. For the purposes of data comparison, it is important to note that the aforementioned conditions likely cause a decreased overall visual potential and, for this reason, patients with such ocular conditions are typically excluded from IOL studies. However, we elected to include these patients, given our small sample size.

Preoperative consent was obtained and a full ophthalmologic examination was performed, including tonometry, visual acuity, refraction, keratometry, and dilated fundus examination. Preoperative cylinder was measured by various methods of quantifying corneal topography and used in preference of reliability; manual keratometry was chosen over IOL Master, which was chosen over Pentacam keratometry. Postoperative visual acuity was measured by manual refraction. Surgeries were performed by multiple second- and third-year ophthalmology residents of the Department of Ophthalmology, Mason Eye Institute, under the supervision of multiple attending cataract surgeons. Primary outcomes were UDVA (uncorrected distance visual acuity) and CDVA (corrected distance visual acuity). Secondary outcomes included reduction in cylinder (i.e., astigmatism). Outcomes were assessed in a retrospective fashion by chart review. Data were inputted into a standard database and statistical analyses were performed by the authors.

Results

Toric IOLs were implanted in 48 eyes of 32 patients. Data were analyzed from follow-up visits, typically occurring at one month and six months after surgery. It should be noted that initial postoperative data were recorded at variable visit intervals, ranging from 7 to 90 days after cataract surgery, with the majority of visits occurring at 30 days (32 of 48 eyes). These dates of the initial postoperative visit were analyzed together as the postoperative visit recorded that was closest to 30 days. Average preoperative cylinder was 2.04D (range: +1.00D to +4.75D). Average postoperative cylinder was 0.93D (range: +0D to 5.25D). The mean reduction in cylinder was 55%. Using the 30-day postoperative visit data, the average best-corrected visual acuity (BCVA) was 20/25 and the average uncorrected visual acuity (UCVA) was 20/30. At one month, UCVA of at least 20/25 was achieved in 50% of the eyes (24 of 48) and BCVA of 20/25 or better was achieved in 79% of the eyes (38 of 48 eyes). Regardless of the postoperative visit date, the overall rate of a UCVA of at least 20/40 was 88% (42 of 48 eyes).

Surgical complications were rare. Most pertinent to the evaluation of toric placement success, an increase in refractive cylinder following surgery occurred in two eyes, one of which was clinically significant. With regard to the surgery itself, two eyes had zonular dehiscence, and one patient was later noted to have a vitreous band to the surgical wound.

Discussion

We sought to evaluate outcomes of toric lens placement by ophthalmology residents and compare these outcomes to previously measured outcomes performed by experienced surgeons. The resident surgeons at the University of Missouri ophthalmology residency program achieved visual acuity outcomes in cataract surgery with toric IOL comparable to those reported by other teaching institutions evaluating such outcomes. An analysis of the VA population at the Bascom Palmer Eye Institute, University of Miami, found 80% of cases with final spherical refraction within 1.0D of target refraction, and ultimately 92% of cases achieved BCVA at least 20/50, with a 56% mean reduction in refractive cylinder (mean preoperative cylinder 2.4D; mean postoperative cylinder 1.1D).⁶ The Dallas Parkland Health and Hospital population of 79 cases, studied by Roesch et al. (University of Texas Southwestern Residency Program), consistently had an 82% reduction in refractive cylinder (mean preoperative 2.13D; mean postoperative 0.38D), with 57% of eyes having a postoperative UDVA of 20/25 or better and 90% having a UDVA of 20/40 or better. CDVA was 20/25 or better in 92% of eyes.⁷ A third large VA population of 105 eyes (Brown University residency program) did not report mean pre- and postoperative values for refractive cylinder, but noted a mean discrete reduction of 1.13D, which appears comparable to other published studies.⁸

In comparison to accomplished surgeons, our residents were able to achieve a similar improvement in visual acuity. A meta-analysis of 11 studies evaluating toric placement found that toric lenses were universally associated with an improvement in visual acuity, but concluded that the lack of standardization of study methods and measurements and small sample sizes make direct comparisons of outcomes difficult. In addition, these studies had more extensive exclusion requirements than our own. The five studies that evaluated operative change in cylinder reported mean reductions ranging from 60% to 78%.⁴ A randomized parallel group study of toric IOL versus control IOL placement in 517 eyes, performed by experienced surgeons, demonstrated a reduction in the mean cylinder that ranged from 57.1% to 65.0%, depending on the choice of power. The data are again similar to our own findings. This study also found that 61% of patients with toric IOLs had spectacle-free distance vision at six months, as compared to 39% of patients who received the control IOL, made by the same manufacturer.⁹

Among the strengths of our study of visual outcomes with the toric lens is that the resident surgeons performing the cataract surgery were at different stages of ophthalmology residency training and were under the supervision of different attending surgeons, likely typifying the true practice of resident-performed surgeries. Another strength of our study is that we used the outcome of uncorrected visual acuity, which is an ideal target for the study of postoperative results, as uncorrected visual acuity highlights the most important outcome for both the patient and the surgeon: the patient is not subjected to the further burden of another procedure or of the need for constant spectacle use. Challenges to the study include the small sample size, all-male gender, the inability to exclude patients with pre-existing conditions with visual significance, and the fact that the procedures assessed were performed several years ago and surgical techniques have since evolved. Additionally, the retrospective nature of the study led to incomplete data collection. In future studies it would be helpful to include a larger, more diverse study population and to compare the standard IOL with the toric lens, each performed in association with further modifications such as LRI, PRK or LASIK. Studies of this nature pose obvious difficulties in standardization and control, which may preclude their development. Of note, one area that has not been frequently reported is the proportion of patients who are spectacle free following surgery and how this may affect quality of life. It would be equally helpful to examine the benefit-cost analysis of the “premium” toric lens versus the standard lens plus any additional procedure or spectacle costs to achieve BCVA.

Conclusion

Toric lenses provide the opportunity for reduced spectacle dependence following cataract surgery in a greater proportion of patients than was ever possible with a traditional IOL. The selection of appropriate patients, preoperative counseling, surgical planning, and operative technique for these lenses are important skills for residents to acquire and practice. The findings of our study show that our residents can execute the preparation and procedure for these “premium” lenses in a way that corrects vision at a level comparable to that achieved by other surgeons. Resident-performed cataract surgery with toric lens replacement appears to pose no additional risk to the patient than a standard surgery.

Biography

Meryl Sundy, MD, (top left), is currently a resident in ophthalmology at Casey Eye Institute, Oregon Health and Science University, Portland. She is a 2014 graduate of the University of Missouri School of Medicine. Dustin McKnight, MD, (top right), is a comprehensive ophthalmologist in private practice in Liberty, Mo. He completed his ophthalmology residency in 2014 at the Department of Ophthalmology, Mason Eye Institute. Craig Eck, MD, (bottom left), is currently a resident in ophthalmology at St. Louis University Eye Institute. He is a 2014 graduate of the University of Missouri School of Medicine. Frank Rieger, III, MD, (bottom right), MSMA member since 1995, is chief of the ophthalmology service at Harry S. Truman Memorial Veterans’ Hospital, Columbia, Mo.

Contact: RiegerF@health.missouri.edu