Anterior segment tomography shows utility in predicting poor outcomes with premium lenses
Retrospective analysis indicated measurement of total corneal irregular astigmatism could be useful in ruling out implantation of the IOL in certain patients.
ReSTOR apodized diffractive premium IOLs from Alcon are beneficial premium lens implants when they work as intended. However, for various reasons, some patients’ expectations are not achieved. The utilization of multifocal lens implants for all cataract patients is only 7%, in part due to the lack of predictability as to who may be happy or unhappy.
Preoperative factors such as dry eye, corneal scarring, map-dot-fingerprint dystrophy, guttatae, diabetic retinopathy, glaucoma, macular degeneration and epiretinal membranes often make patients poor candidates for multifocal lenses. Intraoperative attention to detail in terms of astigmatism control, wound architecture, capsulorrhexis centration, capsular integrity and IOL centration, as well as preoperatively achieving perfect lens calculations, is essential for success.
Postoperative issues such as dry eye, residual refractive error, capsular opacity, IOL centration and cystoid macular edema may significantly impact success. Even in cases in which all of these variables are minimized, a subset of patients with suboptimal results exists. A method for precisely predicting which patients will fall into this subset has yet to be found. Just like most other refractive surgeries, we would all love to find the elusive preoperative measurement that could guarantee success with ReSTOR multifocal lenses.
Measuring corneal irregular astigmatism
Recently, there have been numerous postings on the American Society of Cataract and Refractive Surgery and Kera-net chat rooms discussing the importance of using the Pentacam (Oculus) measurement of total corneal irregular astigmatism at the 4-mm zone to help decide whether a patient is a good candidate for the ReSTOR. U.S. physician labeling for the ReSTOR warns that patients with significant preoperative or expected postoperative astigmatism may not achieve optimal outcomes, and physicians are encouraged to consider alternatives for patients with significant irregular corneal aberrations.
Ophthalmologists online have said to use caution if the total corneal irregular astigmatism measurement is greater than 0.4 µm, and extreme caution should be used if this measurement is greater than 0.5 µm. In fact, Oculus recommends caution if the total corneal irregular astigmatism is greater than 0.3 µm.
Upon hearing about the total corneal irregular astigmatism measurement we reviewed the literature, only to find that there was no information in the peer-reviewed journals and only a few postings in non-peer-reviewed journals. Because this was a measurement about which we had not been previously educated to evaluate, we retrospectively analyzed 389 eyes implanted with the ReSTOR in our practice since Jan. 1, 2011. All of the patients had Pentacam measurements taken preoperatively, as we routinely began doing this for all ReSTOR patients at that time.
Of the 389 eyes implanted with ReSTOR, there were 12 eyes of eight patients with a total corneal irregular astigmatism of 0.4 µm or greater. None of the eight patients were happy with their results, despite some of them having had postoperative interventions such as LASIK or PRK enhancements, YAG capsulotomies, and punctal plugs to improve their outcomes.
Image: Elkins BS and colleagues
Three of the eight patients only had the IOL implanted in one eye because of dissatisfaction with their results. Of the eight patients with total corneal irregular astigmatism greater than 0.4 µm, two had Pentacam measurements that were borderline suspicious for keratoconus, and two had preoperative measurements that should have been repeated because of poor quality and centration issues.
Although we have always been careful to rule out keratoconus, this review emphasizes the critical nature of ruling out forme fruste keratoconus preoperatively. We may do PRK instead of LASIK for our refractive surgery patients if they have suspicious preoperative Pentacam measurements. Similarly, after reviewing these cataract patients’ charts, we strongly discourage implanting a ReSTOR lens if the preoperative Pentacam measurement for total corneal irregular astigmatism is greater than 0.4 µm.
Interestingly, one unhappy patient in our review had a total corneal irregular astigmatism less than 0.4 µm in the operative eye, but the non-operative eye had a total corneal irregular astigmatism greater than 0.4 µm. These types of patients with suspicious preoperative total corneal irregular astigmatism should be treated in a manner similar to how we would treat a LASIK patient with a suspicious preoperative Pentacam in one eye. We recommend that neither eye should have a ReSTOR unless both eyes have total corneal irregular astigmatism less than 0.4 µm. We also do not recommend implanting a ReSTOR lens if the Pentacam measurements are off-center or of poor quality.
In addition to the previously mentioned eight patients, there was a patient who had a preoperative total corneal irregular astigmatism of only 0.155 µm. The patient had had limbal relaxing incisions (LRIs) during her cataract surgery, during which a macroperforation occurred that required suturing. Postoperatively, she did poorly. Her postoperative total corneal irregular astigmatism was now 0.418 µm. This case is interesting because it demonstrates the significance of LRIs and postoperative corneal regularity. ReSTOR patients seem to do poorly with irregular corneas. Thus, caution is advised when it is known that irregularity will increase.
If the toric ReSTOR is approved by the U.S. Food and Drug Administration, it may be a beneficial device because it may reduce the need for LRIs and thus possibly prevent induced irregular astigmatism. Perhaps a similar argument could be made for LRIs made by a femtosecond laser, should such LRIs prove to induce less irregular astigmatism than manual LRIs.
These measurements also emphasize the importance of carefully analyzing preoperative irregular astigmatism in post-refractive surgery patients. On the whole, we have been discouraged with our results in post-RK, PRK and LASIK ReSTOR patients. We do not usually implant ReSTOR in post-RK or post-hyperopic LASIK patients, and we remain cautious utilizing ReSTOR in post-myopic LASIK patients. Looking ahead, it will be interesting to see if these post-refractive surgery patients could be stratified into good and bad candidates utilizing total corneal irregular astigmatism as one of the factors in making this decision.
We look forward to others publishing prospective studies in this area. By measuring preoperative total corneal irregular astigmatism, we can all hopefully make better decisions for our potential ReSTOR patients, thereby improving outcomes and preventing poor results.