November 2018

NEWS & OPINION

Chief medical editor’s corner of the world
Astigmatism matters


by Eric Donnenfeld, MD, EyeWorld Chief Medical Editor


Eric Donnenfeld, MD

“Our goal as refractive cataract surgeons is not to merely give patients vision they will tolerate but to exceed expectations.”
 

The extraordinary advances in improving the safety of cataract surgery over the last decades have completely changed the perception of this procedure. Not too long ago, for most patients, cataract surgery was considered the defining moment of old age with an associated fear of a high risk of complications, loss of quality vision, and high postoperative astigmatism. Aphakic spectacles have given way to tremendous advances in IOL technology and intracapsular and extracapsular surgical technique, and their related high risk of complications has been replaced by phacoemulsification and femtosecond laser technology for some. A-scans and older IOL calculation formulas have been replaced by optical biometry and fourth-generation formulas. Previously, cataract surgery was performed when a patient could no longer function. Today, improving quality of life is the yardstick we use for discussing the option of cataract surgery. Cataract surgery for many patients is a modern fountain of youth.
For many ophthalmologists and their patients, the rate-limiting step to modern refractive cataract surgery is astigmatism management. From my perspective, post-surgical astigmatism has very little redeeming value. Some may argue that a small amount of with-the-rule astigmatism provides increased depth of field at near. However, in all cases post-surgical astigmatism reduces quality of vision at distance. The loss of quality of vision occurs with all IOLs but is significantly greater with presbyopic IOLs. There are three corneal sources of post-surgical astigmatism: preoperative anterior corneal astigmatism, preoperative posterior corneal astigmatism, and surgically induced corneal astigmatism. In addition, a tilted IOL or a malpositioned toric IOL may induce postoperative astigmatism. We now have better measuring devices for evaluating cylinder preoperatively and intraoperatively as well as new techniques for treating astigmatism postoperatively.
Statistically, 50% of our cataract surgery patients have 0.75 D of astigmatism or more.1 I have found that most patients can tolerate postoperative astigmatism of 0.50 D or less, but there are some patients who are more visually demanding that require treatment for even half a diopter. Most of us would not want a pair of glasses that was off by half a diopter. Why shouldn’t refractive cataract surgery patients be equally demanding? Our goal as refractive cataract surgeons is not to merely give patients vision they will tolerate but to exceed expectations. For this reason, I often find myself fine tuning cataract patients who have good results with even half a diopter of residual cylinder.
A common belief about refractive cataract surgery is that patients will tolerate small refractive errors after cataract surgery. In fact, nothing could be further from the truth. Patients with presbyopia-correcting IOLs are more sensitive to even minor refractive errors and especially residual astigmatism. If we want to offer refractive cataract surgery, we have to be able to hit our mark surgically and be willing and able to treat small amounts of post-surgical cylinder. For some patients I have simply developed a zero-tolerance policy when it comes to residual astigmatism.
Most of us realize that patients have higher expectations of their cataract surgery and are more demanding than ever before. I think this is a good thing. Ophthalmologists who successfully transition from cataract to refractive cataract surgery do so because they pay attention to the details that improve their patients’ visual outcomes. For many of us, this means learning to effectively prevent and treat astigmatism.

Reference

1. Ferrer-Blasco T, et al. Prevalence of corneal astigmatism before cataract surgery. J Cataract Refract Surg. 2009;35:70–5.

Contact information

Donnenfeld
: ericdonnenfeld@gmail.com

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