BLOG: Want better vision after cataract surgery? Then flex that wrist, doctor
Read more from John A. Hovanesian, MD, FACS.
Across the United States, about two-thirds of cataract surgeons perform refractive cataract surgery, offering astigmatism correction, toric implants or presbyopia-correcting IOLS.
But many of us miss out on an opportunity to refine our patients’ astigmatic outcomes simply by moving our main cataract incision to approximate the steep axis of preoperative corneal astigmatism.
Moving your main incision to the appropriate axis works whether you are using a femtosecond laser or traditional instruments to perform surgery. It takes us only slightly outside our comfort zone, and it can make a real difference to patients.
Here’s an example of the benefit: A patient whose preoperative keratometry readings reveal 0.5 D of steepness at 90° undergoes cataract surgery. Assuming his surgeon’s main incision will induce 0.5 D of flattening wherever it is placed, this amount will either be added to or subtracted from the patients’ pre-existing corneal astigmatism. If the surgeon puts his incision at the temporal limbus (at 180° for the right eye or 0° for the left), the astigmatism will be doubled, leaving the patient with 1 D of astigmatism to be corrected with glasses.
On the other hand, if the surgeon is comfortable moving his incision to 90°, the patient’s astigmatism will be eliminated.
For this patient, moving the main incision 90° makes a 1 D difference in his astigmatic outcome – the difference between about 20/30 and about 20/20 uncorrected acuity. That’s an amount worth working for.
Not every surgeon is comfortable operating at the 90° axis. This can be accomplished either by moving your seated position to the head of the bed or by tilting your wrist and operating from the side.
I recommend each surgeon come up with a range of comfortable operating axes. Being a right-handed surgeon, mine is from about 165° (that’s a little shift to my left) to about 90° (a bigger shift to my right). For patients whose steep axis falls within that range, I can reduce their astigmatism with my main axis.
What about patients whose steep axis lies between 90° and 165°? For them, the best choice is to make the incision 90° away from their steep axis and then do a limbal-relaxing incision on the steep axis to eliminate the preop astigmatism, plus the 0.5 D I have induced.
Example: A patient who has 0.5 D of steepening at 135° would have his incision placed at the 45° axis. That incision induces 0.5 D of flattening at 45°, which equates to 0.5 D of further steepening at 135°. So we would then do limbal-relaxing incisions to correct now a full 1 D of steepening at 135°.
This very same principle works as well with toric lenses, allowing us to most predictably reduce astigmatism without the optical aberrations induced by obliquely oriented astigmatic corrections, such as happens when you put a temporal incision at 180° and a toric lens at some axis other than 90°.
Whether you are a surgeon who prefers astigmatic keratotomy, one who offers toric implants, or one who implants presbyopia-correcting lenses, the ability to adjust the placement of your main incision is a simple favor that you can easily adopt to permanently benefit your patients’ vision.