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Management of your patients' astigmatism
Third in a series of the top 10 reasons for poor premium IOL outcomes and how to remedy them.
Now that you have mastered the fine art of managing patient expectations and the premium preoperative evaluation, the next critical step to a happy patient is knowing when and how to treat astigmatism.
When addressing astigmatism, it is crucial to differentiate between corneal and lenticular astigmatism. As part of the premium preoperative evaluation, corneal topography is essential to make this distinction. Obviously, if there is no corneal astigmatism preoperatively, all or most of the refractive cylinder will be treated with the removal of the cataract. Managing corneal astigmatism then becomes the real driver to a successful visual outcome.
Mitchell A. Jackson, MD
Upgrading your patient
The next hurdle is to decide how to upgrade your patient, whether it be by using a toric IOL or a presbyopia-correcting IOL with limbal relaxing incisions (LRIs) and/or secondary laser vision correction (LASIK/PRK). It is the surgeon’s responsibility to do a thorough preoperative lifestyle analysis of the patient. Again, it is all about the patient’s postoperative expectations. If the patient has moderate to high astigmatism and, for example, is a retired avid golfer, then the toric IOL might be a better selection. On the other hand, if the patient likes to read extensively, a presbyopic IOL with LRI/laser vision correction might be a better choice. Of note, the Alcon AcrySof IQ toric IOL recently received U.S. Food and Drug Administration approval for an expanded range for treatment of corneal astigmatism up to 6 D at the IOL plane and 4.11 D at the corneal plane. Remember to use the vector analysis calculation for toric IOL calculation, which can be found at www.acrysoftoriccalculator.com.
In the U.S. there are currently no FDA-approved toric accommodating or multifocal IOLs to address astigmatism and presbyopia simultaneously. If the decision is to proceed with a presbyopia-correcting IOL, preoperative corneal astigmatism needs to be addressed. In my experience, uncorrected astigmatism of 0.75 D or greater will usually reduce near and/or intermediate vision results by two or more lines.
Correction methods
LRIs are a quick and easy procedure that can be performed at the time of cataract surgery or at the slit lamp postoperatively to correct corneal astigmatism. If there is less than 0.75 D cylinder preop, consider performing an on-axis corneal surgical incision if the astigmatism axis is within 15° of the intended incision. If the astigmatism axis is outside 15° from the intended incision, place the main surgical incision where comfortable and perform LRIs. For 0.75 D to 1.50 D cylinder preoperatively, perform intraoperative LRIs. For cylinder more than 1.50 D, consider intraoperative LRIs to “debulk” astigmatism along with postoperative laser vision correction.
A great tool provided by Abbott Medical Optics is its LRI calculator software, found at www.lricalculator.com, which provides the necessary adjustment based on vector analysis and incision size and location. Various LRI nomograms are available, such as the “DONO” nomogram (Eric D. Donnenfeld, MD), which allows for more incisional treatment in younger patients and less in older patients. Another popular LRI nomogram can be found on Mastel’s website, www.mastel.com/pdf/napa.pdf (Louis D. “Skip” Nichamin, MD), and adjusts for age and pachymetry.
My preferred method for LRIs postoperatively is at the slit lamp with a diamond blade from Accutome angled for such positioning and preset at 500 µm to 600 µm. The ORange intraoperative wavefront aberrometer (WaveTec) provides an additional advantage of intraoperative real-time refinement by extending or deepening initially placed LRIs. Mark Packer, MD, showed a 27% increased need to extend LRIs with intraoperative aberrometry measurement, potentially preventing the need for a second office procedure, added chair time and reduced profitability.
Another option for correcting astigmatism is laser vision correction. The timing of such should be based upon refractive and topographic stability, typically requiring a minimum of 3 months postoperatively but no less than 1 month. PRK may be the preferred method for laser vision correction, especially in patients with corneal epithelial dystrophy and/or thin corneas, emphasizing the need for a thorough preoperative evaluation inclusive of corneal topography. In my experience with good preoperative axial length measurements and IOL calculations, most laser vision correction “enhancements” are mixed astigmatism, avoiding the need for more costly wavefront treatments.
In the end, untreated residual corneal astigmatism is detrimental to the outcome expected from your patient with a premium IOL. Proper patient expectation, preoperative evaluation and astigmatism management are the first three solutions required for the proper premium result. Stay tuned for the next installment of this series, which will focus on managing posterior capsular opacification and the proper timing for YAG treatments.
Mitchell A. Jackson, MD, can be reached at Jacksoneye, 300 N. Milwaukee Ave., Suite L, Lake Villa, IL 60046; 847-356-0700; fax: 847-589-0609; email: mjlaserdoc@msn.com.
Disclosure: Dr. Jackson has no relevant financial disclosures.