This article is more than 5 years old. Information may no longer be current.
What is the best way to calculate IOL power for cataract surgery?
Marjan Farid, MD, and William B. Trattler, MD, explain their preferences for meeting patient expectations.
Click Here to Manage Email Alerts
Welcome to another edition of CEDARS/ASPENS Debates. CEDARS/ASPENS is a joint society of cornea, cataract and refractive surgery specialists, here to discuss some of the latest hot topics in ophthalmology.
As cataract surgical precision improves, the bar continues to be raised for surgeons to attain the best outcome possible. Advancements in techniques and technology provide the tools, but there is another aspect that is just as important, the decision-making. Biometry is much more precise, but this does not mean much if the IOL calculations are not done properly. Recently, there have been numerous new IOL formulas to help surgeons select the proper IOL, but this has added more confusion for the surgeons. This month, Marjan Farid, MD, and William B. Trattler, MD, discuss how they calculate IOL power for cataract surgery. We hope you enjoy the discussion.
Kenneth A. Beckman, MD, FACSOSN CEDARS/ASPENS Debates Editor
Broad range of formulas needed for different eyes
For the standard average axial length eye, I like to use the Holladay 1 formula as it is consistent and works well for the majority of those cases. For short eyes that have axial lengths below 22 mm, I mainly look at the Hoffer Q formula as I think it provides superior prediction for short eyes. With the Barrett II Universal formula, we can now encompass the majority of the long axial length eyes as well and get better predictability throughout a greater range of axial length and keratometry readings. I think the Barrett II Universal formula will give us the closest thing to a one-stop shop for the majority of cases.
Eyes that previously underwent laser refractive surgery continue to pose a challenge for IOL prediction. The Barrett True-K formula has stood out as a leader for IOL prediction in this group. I still like to compare this with the ASCRS formula as well to broaden my confidence level in lens selection. However, there seems to be equal if not better prediction with the Barrett True-K formula.
Finally, I use ORA wavefront aberrometry (Alcon) on all post-refractive eyes as well as premium IOL cases. The ORA provides a final assessment and check for eyes in the post-refractive category. I feel like using a broad range of formulas, adjustment factors and intraoperative wavefront aberrometry in difficult post-refractive eyes gives me the most confidence in terms of final IOL selection. Furthermore, the patient can appreciate the difficulty in assessing the IOL power and the multiple checks that the doctor has gone through in order to give them the best possible outcome.
- For more information:
- Marjan Farid, MD, can be reached at Gavin Herbert Eye Institute at the University of California, Irvine, 850 Health Sciences Road, Irvine, CA 92697; email: mfarid@uci.edu.
Disclosure: Farid reports she is a consultant for Johnson & Johnson Vision, Allergan, Shire, Bio-Tissue, Kala and SightLife Surgical
Latest technologies and IOL formulas can help meet expectations
Patients have high expectations with cataract surgery. They expect a painless procedure, they expect to be comfortable after the procedure, they expect rapid visual recovery, and they expect to have excellent uncorrected vision. The good news is that for many patients, we can meet these expectations. In particular, we have found that preoperative and intraoperative NSAIDs can help patients by reducing or eliminating intraoperative and postoperative pain. There have also been a number of innovations over the past decade that can help speed visual recovery. These include placement of viscoelastic on the cornea during and immediately after the procedure to help maximize ocular surface smoothness. Another improvement has been reduction in phaco energy delivered during surgery, which results in less early postoperative corneal edema. This has occurred with advances and improvements in phaco energy delivery, as well as advances in manual disassembly including phaco chop and the miLOOP (Iantech). Preoperative use of topical steroids, as well as on the day of surgery, has also helped reduce corneal swelling, leading to faster visual recovery. Of course, one of the most critical aspects of meeting patient expectations is to end up on target with excellent uncorrected visual acuity. With that in mind, an overview of steps and techniques to optimize visual outcomes will follow.
Numerous advances have led to improvements in visual outcomes after cataract surgery. In 2010, data from a study by SurgiVision DataLink found that less than 75% of eyes implanted with a Crystalens (Bausch + Lomb) or multifocal IOL achieved 20/25 or better vision. In other words, more than 25% of eyes receiving presbyopic IOLs ended up with 20/30 or worse uncorrected distance vision. Over the past 7 years, there have been significant advances that have improved visual outcomes, especially for patients receiving a presbyopic IOL. One major change has been the focus on the identification and treatment of dry eye before performing final biometry and keratometry readings because dry eye appears to be a common finding in patients scheduled for cataract surgery. Treating dry eye in cataract patients improves keratometry readings.
A second major advance in improving visual outcomes has been improved diagnostic technologies. Over the past decade, improvements in noncontact biometers have led to successful imaging in a higher percentage of eyes, even eyes with advanced cataracts, allowing us to limit the number of eyes that have their axial length measured with contact ultrasound, which provides less accurate axial length measurements. As well, we have seen improvements in measuring keratometry and astigmatism. Biometers have improved their accuracy at measuring keratometry. As well, devices such as the Cassini (i-Optics), Pentacam (Oculus) and Galilei (Ziemer) can measure the posterior corneal shape, which can vary from patient to patient. With improved keratometry readings, astigmatism can be more accurately measured and treated at the time of surgery, which improves visual outcomes. We have also seen improvements in identifying and marking the axis of astigmatism for surgery, with intraoperative technologies such as Verion (Alcon), Callisto (Zeiss), ORA (Alcon), TrueVision (TrueVision Systems) as well as Lensar (Lensar), which uses iris registration. All of these technologies provide incremental improvements in visual outcomes.
Perhaps the most significant development in improving visual outcomes with cataract surgery has been the advance in IOL calculation formulas. A recent retrospective study of more than 18,000 eyes evaluated a number of IOL formulas and found that the Barrett Universal II formula provided the best uncorrected visual outcomes in most scenarios. In this study, all of the formulas worked well when patients had an average axial length, average corneal steepness, average anterior chamber depth and average length thickness. However, when measurements of the eye were not in the average range, there were significant differences in outcomes with available formulas. While this study found that the Barrett Universal II performed the best, it did not look at the Hill-RBF formula, nor the Ladas Super Formula. The Hill-RBF formula uses pattern recognition and other sophisticated mathematical principles to continuously improve and appears to provide a significant improvement over previous generations of formulas. The Ladas Super Formula uses multiple formulas, as well as outcomes data, to optimize the IOL power recommendation. Like the Hill-RBF formula, the Ladas formula can continue to improve outcomes over time as additional outcomes data are incorporated.
At my practice, we are currently using the Argos biometer (Movu) for axial length measurements, as well as the Cassini and Pentacam for total corneal power; both provide iris registration data to the Lensar laser, allowing for registration of astigmatism during surgery. The Argos biometer provides the Barrett Universal II formula, which is the formula we use at our center for virgin corneas.
With high patient expectations, surgeons must work hard to achieve the highest level of visual outcomes and patient satisfaction. Attention to identifying and treating preoperative dry eye is critical. Management of astigmatism with the latest imaging and guidance technologies can lead to significant improvements in visual outcomes. As well, utilization of the latest IOL formulas can significantly improve the percentage of eyes that achieve excellent uncorrected visual acuity. Overall, meeting and exceeding patient expectations in a high percentage of cataract patients is possible with the latest technologies and IOL formulas, and future improvements will hopefully continue to provide even better visual results with cataract surgery.
- References:
- Buznego C, et al. Retrospective comparison of 3177 eyes implanted with presbyopic IOLs. American Society of Cataract and Refractive Surgery annual meeting; April 10, 2010; Boston.
- Epitropoulos A, et al. J Cataract Refract Surg. 2015;doi:10.1016/j.jcrs.2015.01.016.
- Melles R, et al. Ophthalmology. 2017;doi:10.1016/j.ophtha.2017.08.027.
- Trattler WB, et al. Clin Ophthalmol. 2017;doi:10.2147/OPTH.S120159.
- For more information:
- William B. Trattler, MD, can be reached at Baptist Medical Arts Building, 8940 N. Kendall Drive, Suite 400-E, Miami, FL 33176; email: wtrattler@gmail.com.
Disclosure: Trattler reports he is a speaker and consultant for or has a financial interest in Allergan, Alcon, Bausch + Lomb, Argos, Shire, Lensar, Iantech and Oculus.