However, I raised the bar just to be safe. This number is just based on my experience, and hasn’t been proven in a clinical study, and people may say it’s kind of strict. “And I think that a defocus, or spherical error, of 0.5 D following cataract surgery is clinically significant, so any HOAs more than 0.3 µm should make the surgeon worry. “At a 4-mm diameter, 0.3 µm of HOA is similar to the blur produced by 0.5 D of defocus,” he says. Maeda developed a numerical HOA cutoff based on the pupil diameter. To help determine if a patient has too much irregular astigmatism that might make a MF IOL unworkable, Dr. The HOAs also cause image contrast to worsen in some situations.” “The MF IOL divides light into far and near so, even with a perfect cornea, image contrast is reduced to some extent. “Higher-order aberrations are the enemy of the multifocal IOL,” says Dr. The Zeiss-Humphrey Atlas also provides data on corneal HOAs using ray tracing. This faint scar or mild distortion can result in irregular astigmatism that’s not appropriate for the use of a multifocal IOL.” Devices useful for higher-order aberration, a.k.a., irregular astigmatism, measurement include the Oculus Pentacam, which measures corneal irregular astigmatism and the Topcon KR-1W and Nidek OPD-Scan, which separate out lenticular and corneal higher-order aberrations. “Even if a cornea looks perfectly clear, it might have irregular corneal astigmatism due to undetected keratoconus, a very faint scar or mild pterygium. “It’s important to remember that the corneas of your patients aren’t always perfect,” says Naoyuki Maeda, MD, Phd, of Japan’s Osaka University Graduate School of Medicine. Surgeons say one of the top benefits topography and tomography systems offer them is the ability to catch irregular astigmatism, represented by higher-order aberration data, that would diminish the presbyopic IOL’s ability to work well. Here are the top tips from corneal experts on using your topographers and tomographers to help implant premium intraocular lenses. Now however, as cataract surgery leans more toward refractive cataract surgery with the addition of premium lenses, surgeons say that corneal imaging can provide details that can help them predict whether a patient will be successful with a premium lens or if he might be better off with a monofocal. Since its arrival, corneal topography has almost always been associated with refractive surgery. As the pupil diameter increases, so do his higher-order aberrations. Topography of a patient who had previously undergone LASIK for high myopia. Users should refer to the original published version of the material for the full abstract.Figure 1. No warranty is given about the accuracy of the copy. However, users may print, download, or email articles for individual use.
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