Eyeworld

77 EW INTERNATIONAL January 2018 aberration to give greater depth of focus to patients. In patients with multifocal lenses, with special cor- neal or previous refractive surgery, spherical aberration becomes more important. It is well known that multifocal lenses distribute the light in several foci, which contributes to losing between 8 and 20% of the transmitted. All these lenses present a loss of contrast at different distanc- es; it is at this point that it is import- ant to make use of all the resources that can improve contrast sensitivity to give greater visual quality to this group of patients. For the cataract surgeon, it is important to know the corneal asphericity of patients to offer them the best possible result. Concepts to remember • In general, correction of spheri- cal aberration improves contrast sensitivity but decreases depth of focus. • The spherical aberration is greater as the pupil size increases. • For proper correction of corneal spherical aberration, the intra- ocular lens should be perfectly centered. • In view of the possibility of intra- ocular lens deviation, it is pref- erable to use lenses with neutral spherical aberration or IOLs with bi-sign design. • Hyperprolate corneas (Q >0.6) do not use aspherical lenses. EW References 1. Oshika T, et al. Influence of pupil diameter on the relation between ocular higher-order aberration and contrast sensitivity after laser in situ keratomileusis. Invest Ophthalmol Vis Sci. 2006;47:1334–8. 2. Guirao A. Optical aberrations of the human cornea as a function of age. J Opt Soc Am A Opt Image Sci Vis. 2000;17:1697–702. 3. Grimson JM, et al. Contrast sensitivity: es- tablishing normative data for use in screening prospective naval pilots. Aviat Space Environ Med. 2002;73:28–35. 4. Portney V. New bi-sign aspheric IOL and its application. Optom Vis Sci. 2012;89:80–9. 5. Piracha AR. Using angle alpha in premium IOL screening. Cataract & Refractive Surgery Today. 2016;(3):24–25. Editors' note: This article was first pub- lished in ALACCSA-R #24, September/ October 2017, pages 10–15, and is included here with permission from ALACCSA. For more information about ALACCSA, visit www.alaccsa.com. Contact information Orlich: orlichclaudio@hotmail.com Figure 5. CT LUCIA aspherical lens with the "aspheric Zeiss optics" design; information provided by Carl Zeiss Meditec Figure 6. iTrace image; the red cross is the visual axis, the green one represents the center of the pupil (angle = kappa distance between red and green crosses), and the blue cross corresponds to the optical axis or center of the limb (alpha angle = distance between the red and blue crosses) Source (all): Claudio Orlich, MD

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