EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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September 2013 February 2011 EW REFRACTIVE SURGERY 43 Using adaptive optics to customize surgery by Michelle Dalton EyeWorld Contributing Writer Simulating how patients will see without higherorder aberrations is a major advantage to integrating adaptive optics into your practice, expert says T he highly aberrated eye poses numerous challenges for surgeons—not the least among them an increased level of difficulty in obtaining accurate measurements (and, therefore, increased potential for missed corrections). This can be especially daunting in refractive surgery, when patients present with progressively worsening visual distortion. Wavefront testing has proven a useful technology to assess these higher-order aberrations (HOAs) and to better understand the limitations of visual function, but it's not enough. Adaptive optics (AO), however, was originally designed for use in astronomy and is now finding its way into ophthalmology, said Karolinne Maia Rocha, MD, Cole Eye Institute, Cleveland Clinic Foundation, Ohio. Because imperfections in the cornea and lens are unavoidable, AO compensates for the irregularities and improves visual function, she said, by combining two main components: a wavefront sensor that can Suggested reading list 1. 2. 3. Rocha KM, Vabre L, Harms F, et al. Effects of Zernike wavefront aberrations on visual acuity measured using electromagnetic adaptive optics technology. J Refract Surg. 2007;23(9):953-959. Rocha KM, Vabre L, Chateau N, Krueger RR. Expanding depth of focus by modifying higher-order aberrations as induced by an adaptive optics visual simulator. J Cataract Refract Surg. 2009;35(11):1885-1892. Rocha KM, Vabre L, Chateau N, Krueger RR. Enhanced visual acuity and image perception following correction of highly aberrated eyes using an adaptive optics visual simulator. J Refract Surg. 2010;26(1):52-56. Wavefront measurement: Ocular wavefront aberrations are recorded while the deformable mirror is set to an aberration-free shape; user-defined aberrations are applied (0.6 µm of spherical aberration for a 6-mm pupil diameter is applied and kept constant for visual simulation). Source: Karolinne Maia Rocha, MD measure and correct both lower and higher-order aberrations and a deformable mirror that compensates for the wavefront error in a dynamic fashion. A patient's optical system irregularities are likely responsible for the variable and limited visual performance in patients with keratoconus or in symptomatic postoperative refractive surgery eyes. In the past, the size and design of the devices used somewhat limited the potential and mostly bench scientists used AO, she said. However, more compact designs are being evaluated (although none are yet approved in the U.S.) and are generating interest from clinicians and bench scientists, she said. "It's a way we can mathematically measure the effect of aberrations on the visual performance," Dr. Rocha said, and by using AO simulators, clinicians can assess individual HOAs in their offices, mathematically "correct" them and simulate the possible surgical correction in the office, she said. "In highly aberrated eyes, AO allows you to show patients a simulation of what their vision could be if the errors are corrected. We can explore in a clinical setting the maximum subjective potential for custom vision correction. Sometimes the patients will read upward of 2-3 lines better," Dr. Rocha said. Perhaps more important than helping the clinician, however, is AO's ability to help patients understand what their visual aberrations are and what their vision could be like without them. Dr. Rocha uses the crx1 (Imagine Eyes, Orsay, France) and has had success with it "in both normal and highly aberrated eyes. The ability to assess the limits of human vision by manipulating and correcting ocular aberrations can also help us predict the potential benefits of custom treatments and neuroadaptation." Since both spherical aberration and pupillary diameter manipulation can have a great impact on depth of focus, this type of technology may be most helpful when treating presbyopes, she added. Dr. Rocha's group found introducing both positive and negative spherical aberrations with AO expanded patients' depth of focus overall in a study (see suggested reading list). "Spherical aberration increases depth of focus and has a positive impact on presbyopia correction," she said. "AO technology can simulate the right amount of spherical aberration that would not interfere with the patients' distance vision and still increase their depth of focus and pseudoaccommodation." She predicts this type of simulation will be used in the office as a means of managing patient expectations. aberration) compensate for the cornea, which has an average aberration of 0.28 µm for a 6.5-mm pupil diameter. But one size does not fit all, and using AO will give us a better picture of the aberrations and, therefore, will help us provide even better visual outcomes," Dr. Rocha said. AO technology has potential for customized refractive surgery and presbyopic corneal and lensbased treatments, customized contact lens corrections, and wavefront customized IOL implantation, she said. AO technology can also be applied to retinal imaging, microperimetry and even microlaser treatments, she said. "AO will increase the resolution of retinal imaging devices by a factor of 10, revealing previously invisible retinal microstructures." There's been a few studies published on reflectance of cones, photoreceptor density and microvascular activity, and more are likely to come, Dr. Rocha said. EW Possible uses Editors' note: Dr. Rocha has no financial interests related to this article. AO will likely have the most use in refractive surgery, but other areas hold potential as well. "Wavefront-correcting IOLs (neutral and with negative spherical Contact information Rocha: 216-445-2020, karolinnemaia@gmail.com EyeWorld @EWNews Keep up on the latest in ophthalmology! Follow EyeWorld on Twitter at twitter.com/EWNews