Hill, MD, medical director of East Valley Ophthalmology in Mesa, Arizona, notes that when choosing a toric IOL, it’s helpful to first determine whether the type of astigmatism the patient has is appropriate. “I’d also be reluctant if there’s a probability of keratoconus, or in the presence of major ocular pathologies like gliosis, macular degeneration or diabetic retinopathy.” “I’d hesitate to implant a toric lens if irregular astigmatism is involved,” he adds. Dick recommends using one of the established online calculators, such as the Donnenfeld calculator, to make a decision about whether a toric lens is really indicated for a given patient. Of course, if it’s a markedly skewed radial axis, as it could be in a case of keratoconus, then the patient might not be a great candidate for a toric lens because toric lenses have radial symmetry.”ĭr. We also use the manifest refraction to guide us in our decision-making, in terms of what the patient will accept at the spectacle plane. In the case of asymmetric bow ties, we’d be conservative and treat the least amount of astigmatism in the hemi-meridian, as opposed to the full amount in the opposing hemi-meridian. “A toric lens may not be able to address irregular astigmatism adequately,” he points out. Waring notes that whether or not a toric IOL is a good solution for an eye with irregular astigmatism depends on the specifics of the eye in question. “A macular OCT is also valuable for checking to see if the patient has, for instance, macular gliosis, which predisposes to postoperative macular edema, and thus considerable patient dissatisfaction.”ĭr. “This is of prime importance when smaller degrees of astigmatism are at issue, which is true in most of our cases,” he notes. Burkhard Dick, MD, PhD, FEBOS-CR, director and chairman of the University Eye Hospital in Bochum, Germany, believes that corneal tomography, which assesses both anterior and posterior cornea, is very useful. In addition, Hartmann-Shack wavefront aberrometry can give you useful information to supplement the manifest refraction guidance in many cases, but wavefront information certainly isn’t essential.” “Beyond that, because we’re doing lens surgery earlier and earlier, we also consider the manifest refraction in younger patients. “In our practice we factor in the topography by using a weighted mean of the topographic and IOLMaster astigmatism readings,” he continues. Multiple devices can give you this, including the IOLMaster 700, the Lenstar, the Pentacam and corneal OCTs. Ideally, you’d also have the ability to evaluate the total keratometry, which includes the anterior and posterior corneal contribution to the astigmatism. So you need either a topography or tomography device to understand the quantity, quality and orientation of the astigmatism. You need to be able to see it because you won’t necessarily be able to tell whether your patient’s astigmatism is regular or irregular unless you can visualize it. “Astigmatism can be regular or irregular, and regular astigmatism can be against-the-rule, with-the-rule or oblique. “If you’re going to fix astigmatism, you need to be able to measure it and see it,” notes George Waring IV, MD, FACS, founder and medical director of the Waring Vision Institute in Mount Pleasant, South Carolina. In terms of which instruments should be used to make those measurements, a 2019 clinician survey conducted by the American Society of Cataract and Refractive Surgery found that most surgeons, both in the United States and around the world, rely on topography and automated keratometry to guide them in their toric IOL power selection. The first step when deciding whether a toric IOL is appropriate for a given patient-and what power to implant-is measuring the astigmatism of the eye. Here, surgeons with expertise in measuring astigmatism and implanting and aligning these lenses share strategies to improve your outcomes. Originally only available in monofocal designs, torics have now expanded to include multifocal and expanded-depth-of-focus lenses. A mong the many advanced-technology intraocular lenses now available to ophthalmologists, one of the most commonly used is toric lenses.
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