Future looks bright for patients with cataract and their surgeons
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Crisp, clear vision at distance, day and night, is the highest priority for the patient undergoing cataract surgery.
For the patient selecting monovision to reduce dependence on glasses, the need to provide high-quality uncorrected vision in the distance eye is critical. The near eye is more forgiving because of angular magnification and the ability to move near targets in and out to the preferred vertex distance, and mild residual astigmatism can actually enhance depth of focus. For this reason, the enhancement rate after monovision surgery in refractive corneal surgery and refractive cataract surgery is much higher for the distance eye than the near eye.
While residual myopia, hyperopia and astigmatism all reduce quality of vision, as do higher-order aberrations, astigmatism and higher-order aberrations are especially impactful to quality of vision in patients with diffractive and refractive multifocal or extended depth of focus lens implants. Therefore, astigmatism management is a critical skill for the refractive cataract surgeon to master.
Two large U.S. studies, one consisting of 6,000 eyes compiled by Warren Hill, MD, and another evaluating an amazing 45,678 eyes by Guy Kezirian, MD, in DataLink give us insight into the astigmatism present in the typical patient who presents for cataract surgery. Hill reported 19.1% with astigmatism of 0.5 D or less, and Kezirian reported 18.6%. While all of us know that we refract in 0.25 D increments, up to 0.5 D of astigmatism reduces best corrected visual acuity only one line, taking 20/15 to 20/20 or 20/20 to 20/25. Most patients will be 20/happy with 0.5 D of astigmatism or less, and today this is a reasonable surgeon outcome goal. Therefore, about 20% of the time, our goal as a cataract surgeon is to simply not make the patient’s astigmatism worse.
A temporal clear corneal incision of 2.5 mm or less is astigmatism neutral when measured at 1 year, and it is the preferred choice for most surgeons. Unfortunately, about 81% of patients have enough astigmatism that intraoperative or postoperative correction is required for the surgeon driven to the highest level of patient satisfaction. On-axis cataract incisions or some form of bladed or laser peripheral corneal/limbal relaxing incisions are effective in the 33.9% (Hill) or 33.8% (Kezirian) of patients who have 0.5 D to 1 D of astigmatism. In the Kezirian DataLink series, 904 patients who underwent corneal or limbal relaxing incisions for this level of astigmatism achieved a mean outcome of 0.5 D or less residual cylinder.
With more than 1 D of astigmatism, 47% for Hill and 47.6% for Kezirian, we need something more powerful and more accurate. The choices today include a toric IOL, a Light Adjustable Lens (LAL, RxSight), a small-aperture IOL or a secondary enhancement with laser refractive corneal surgery, including LASIK, PRK or SMILE. All give excellent results, but as I review the available data, the LAL and laser corneal refractive surgery generate the highest percent of patients with 0 D to 0.5 D of residual astigmatism after surgery. The small-aperture IOL promises to be especially useful in patients with both regular and irregular astigmatism. I have always relied heavily on LASIK and PRK enhancements in my refractive cataract surgery practice to generate 20/happy results, but I see a great future for the LAL category of IOLs and believe that over the next 10 years, as LAL technology becomes available in monofocal, multifocal, EDOF and accommodating IOLs, it will dominate. Once that occurs, we can ratchet our postoperative target down to 0.25 D or less of residual postoperative astigmatism and sphere with few laser corneal enhancements required. In the near future, refractive cataract surgery will generate outcomes as good as or better than refractive corneal surgery, resulting in increased surgeon and patient preference for this approach.
When I first started monitoring my post-cataract surgery astigmatism outcomes after extracapsular cataract extraction in 1980, my outcome target was less than 2 D of astigmatism, using a Terry keratometer on every case to adjust suture tension. When I adopted phacoemulsification and rigid posterior chamber IOLs, I moved to a target of 1 D or less of residual astigmatism. Clear corneal sutureless phacoemulsification with foldable IOLs moved me to a 0.5 D residual astigmatism target. In the lifetime of the cataract surgeon completing training today, the target will be less than 0.25 D of sphere and cylinder and higher-order aberrations less than 0.25 root mean square in every patient.
With a good macula and an accommodating IOL, nearly every patient who undergoes cataract surgery will be 20/20 or better seamlessly from far to near. The mean age of cataract surgery will plummet, and loss of accommodation and reduced contrast sensitivity will become the indication for natural lens replacement surgery. Most procedures will be immediate sequential bilateral surgery in an ASC or office-based suite. Medicare will be happy because Medicare eligibility will increase to age 70 years, and patients will be presenting for surgery in their 50s and 60s. The majority of the fees will be the patient’s responsibility, just like LASIK, PRK and SMILE today. To me, that is an extremely bright future, and I look forward to living long enough to both see it happen and benefit from it.
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