Eyeworld

4 Presbyopia correction: Exploring surgical options, expectations, and postoperative error by Daniel Chang, MD Addressing expectations for range of vision and visual quality Emerging technology presents new opportunities to reduce aberrations T he goal of pres- byopia-correcting surgery is to increase patients' range of vision while main- taining good visual quality. Tradeoffs in visual quality and night vision symptoms should always be considered when correcting presbyopia, but advances in technology have provided more and better options for patients. To achieve patient sat- isfaction, surgeons not only need to set patients' expec- tations, but also choose lens designs and materials that will meet patients' needs. Patient selection and counseling When selecting patients for presbyopia correction, surgeons should consider objective factors such as the patient's preoperative refrac- tive error, cataract severity and type, ocular surface qual- ity, macular health, and even the patient's height and arm length and where he or she prefers to hold devices and reading materials. Subjective- ly, factors such as the patient's personality, profession, and hobbies should be considered. These factors help create a picture of what patients hope to achieve with presbyopia- correcting surgery, particularly with respect to their past and present visual experience. They also help me to counsel patients. This is my oppor- tunity to make sure their expectations are reasonable. I explain what the surgery offers, without overpromising. Optimizing outcomes Since extending depth of focus can compromise visual quality, it is important to opti- mize aberrations when cor- recting presbyopia. The cor- nea has spherical aberration, which is typically positive (av- erage +0.27 µm), so surgeons should correct that with a negative spherical aberration IOL, which will minimize the spherical aberration of the eye to maximize visual quality (Figure 1). 1 If the cornea has positive spherical aberration, IOLs with positive spherical aberration will induce greater spherical aberration overall. Furthermore, minimizing chromatic aberration can be more important than spher- ical aberration. 2,3 Significant chromatic aberration in an IOL affects all patients, preventing the colors of light from focusing sharply on the retina (Figure 2). The patient's visual acuity may be 20/20, but vision will not appear sharp, particularly in low-con- trast situations. Refractive lenses, in- cluding the cornea and lens, induce chromatic aberration. Since chromatic aberration is additive, surgeons should se- lect IOL materials that induce as little chromatic aberration as possible. Low- and mid-in- dex materials tend to have better chromatic aberration properties, and some IOLs induce less chromatic aberra- tion than the human lenses they replace, resulting in a net reduction in the eye's chro- matic aberration after cataract surgery. To maximize visual qual- ity, surgeons need to choose an IOL that will compensate for corneal spherical aberra- tion and minimize chromatic aberration. Seeking balance When correcting presbyopia, IOLs need to balance the three areas of visual quality, depth of field, and night vision symptoms. Reducing spherical and chromatic aberrations maximizes visual quality, but increasing depth of field decreases visual quality, result- ing in night vision symptoms such as glare, halos, and star- bursts. Traditional higher-add multifocal IOLs provide good depth of field, with good near vision and a slight decrease in intermediate vision. However, this reduces contrast sensitiv- ity and increases night vision symptoms. Reducing the add power decreases the depth of field slightly while improv- ing night vision symptoms. Even though low-add multi- focal IOLs have similar visual quality as traditional multifo- cals, they are now a popular option. With monofocal and even multifocal IOLs, we only have one or two points of focus, respectively, where vision is best. Therefore, with these IOLs, we must nail the target for far, and we have to choose the near focal point (if any) preoperatively. In contrast, an extended depth of focus IOL provides continuous vision for far (driving and watching tele- vision) through intermediate (computer and dashboard) into near (reading and smart- phones). 4 There is a func- tional range of vision that helps meet the range of vision needs for patients whose modern lifestyles involve the use of computers and tablets—even if the refractive outcome is a little off. The currently available extended depth of focus IOL " As industry continues to provide good options, surgeons are better equipped to find the best set of tradeoffs to satisfy our patients. " –Daniel Chang, MD

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