Never before have there been so many great surgical techniques to reduce astigmatism in our patients while simultaneously providing cataract surgery. Astigmatism of 0.50 D exists in up to 72% of our cataract population, and 38% have as much as 1.00 D.1 Residual astigmatism may be responsible for glare, symptomatic blur, ghosting, and halos.2
In the past, many talented surgeons successfully managed astigmatism with limbal relaxing incisions (LRIs) manually created with diamond blades. The few times I tried manual LRIs, I found my results to be variable despite using several different nomograms. I attributed this to a lack of uniformity in the depth and curvature of my incisions.
LASER TECHNOLOGY FOR LRIs
When I heard about femtosecond laser technology and then finally had my first opportunity to use it, my interest in trying LRIs was renewed. Thanks to the technology's optical coherence tomography-guided functionality, studies have shown that the femtosecond laser can generate very reproducible results, both in terms of length and depth, and utter precision in angular position and the optical zone.3
On all of my cases, I continue to use the Donnenfeld nomogram on the LRI calculator offered at www.lricalculator.com (Abbott Medical Optics Inc.). I currently collect my keratometry readings primarily using the IOLMaster (Carl Zeiss Meditec, Inc.) but review preoperative topography and manual keratometry readings to verify the information.
ADJUSTMENTS TO MAKE
The LRI calculator, initially designed for manual LRIs, takes into account the patient's astigmatism and my phaco incision. A current trend when using the laser is to place the arcuate incisions at the 9-mm optical zone more centrally than manual LRIs. Therefore, a slight a mathematical adjustment must be made to the nomogram when entering the variables into the laser. For example, the arc of the incision must be reduced 33% from the Donnenfeld nomogram. It is also recommended that the arcuate incisions be 85% of the depth of the cornea.
Prior to one of my recent cases, James Salz, MD, mentioned to me that he has begun considering using an 8-mm optical zone. It has been his experience that this size works better in small corneas or those with pannus. We agreed that further studies need to be performed to verify the results' consistency, but they look good so far.
I now feel comfortable creating LRIs with a femtosecond laser when I am treating up to 1.50 D of astigmatism. This technique (Figures 1 and 2), using the modified Donnenfeld nomogram, has produced consistent results in my hands. I feel confident knowing I can rely on this technology to manage astigmatism.
Damien F. Goldberg, MD, is in private practice at Wolstan & Goldberg Eye Associates in Torrance, California. He acknowledged no financial interest in the products or companies mentioned herein. Dr. Goldberg may be reached at (310) 543-2611; email@example.com.
- Hill W. Expected effects of surgical induced astigmatism on Acrysof toric intraocular lens results. J Cataract Refract Surg. 2008;34(3):364-367.
- Nichamin LD. Nomogram for limbal relaxing incisions. J Cataract Refract Surg. 2006;32(9):1048.
- Masket S, Sarayba M, Ignacio T, Fran N. Femtosceond laser-assisted cataract incisions: architectural stability and reproducibility. J Cataract Refract Surg. 2010;36(6):1048-1049.