Eyeworld

by Michelle Dalton EyeWorld Contributing Editor Reciprocal zonular action A new theory of accommo- dation is proposed A lthough most ophthal- mologists accept von Helmholtz's lenticular theory of accommoda- tion, there is continuing debate and controversy over the role of the extralenticular elements in ac- commodation including the vitreous and zonule. Understanding the zonular anatomy and its relation- ship to the anterior hyaloid and cil- iary body has been elusive. However, a new theory proposed by Daniel B. Goldberg, M.D., uses computer ani- mation to provide a consolidated theory of the mechanism of accom- modation coupled with his theory on reciprocal zonular action. The theory was recently published in Clinical Ophthalmology, 1 said Dr. Goldberg, clinical associate professor of ophthalmology, Drexel University College of Medicine, Philadelphia, and a founding partner, Atlantic Eye Physicians, Little Silver, N.J. He has also developed a website (www.gold- bergtheory.com) to explain his the- ory in hopes it will lead to better accommodating IOL development. "The computer-generated model supports the concept that the ciliary body/zonule/anterior hyaloid com- plex contributes to the changes in the posterior lens capsule during ac- commodation," he told EyeWorld. Another theory, one that de- bates the role of the extralenticular structures including the ciliary body and vitreous proposed by Dr. Coleman, should be modified in light of the computer modeling, Dr. Goldberg said. "Dr. Coleman was conducting his research at a time when we didn't fully understand the anatomy of the posterior zonule and proposed that accommodative lens changes occurred because of vitreous pres- sure," Dr. Goldberg said. However, a paper published last year 2 used improved scanning elec- tron microscopy and ultrasonic bio- microscopy techniques to identify three components of the vitreous zonule—anterior, intermediate, and posterior—in addition to the pars plana zonule that travels from the ciliary valleys to the attachment zone above the ora serrata (for more on that paper, see "Femto lasers in cataract surgery" in the April 2010 issue of EyeWorld). Using the Croft Study's anatomic definition coupled with an extensive literature search and verifi- cation by ultrasound biomicroscopy on a three-dimensional computer model, Dr. Goldberg's new theory suggested reciprocal zonular action. He notes his theory would have been impossible to visualize and val- idate had it not been for the work of others before him. Moving science forward Dr. Goldberg said "the architecture of the zonules determines the way the forces of the ciliary body con- traction are distributed in shaping the lens during accommodation and disaccommodation;" the three-di- mensional architecture of the zonules was first studied in the late 1970s. The Croft study 2 described a "cleft" between the vitreous mem- brane and the pars plana zonules bridged by zonular fiber bundles those researchers called the interme- diate vitreous zonule. In addition, the anterior vitreous zonule inserts into the posterior lens capsule and anterior hyaloid (Wieger's ligament). The attachment zone is "a multilay- ered, interconnected sponge-like ring where the vitreous attaches to the posterior pars plana and ora ser- rata region," Dr. Goldberg said (see Figure 1). The animated model of accom- modation enables a new perspective and framework to demonstrate and interpret the mechanism of accom- modation. "The engine of accom- modation is the contraction of the ciliary body mediated by the distri- bution of forces via all elements of the zonular apparatus. The resulting changes in refraction are due to the increased thickness of the lens and the increased curvature of the ante- rior and posterior capsule. The com- plex anatomy of the vitreous zonule results in traction on the vitreous membrane peripherally," Dr. Goldberg said. During accommodation, the cil- iary body moves both forward and centripetally, and the posterior zonular attachments simultaneously stretch, affecting the shape changes in the lens. During disaccommoda- tion, the lens returns to its original shape, with the anterior zonules contracting and the posterior zonules relaxing. "There is a reciprocal action of the anterior and posterior zonules," he said. "During ciliary body con- traction, the anterior zonules lose tension, while the posterior zonules stretch and exert force on the poste- rior lens capsule, playing a role in shaping the posterior lens thickness and curvature. During ciliary body relaxation, the posterior zonules lose tension as the lens flattens and is pulled back by the increasing ten- sion of the anterior zonules." Dr. Goldberg hopes others will evaluate his theory and enter into "a robust scientific discussion on the merits (or demerits, as the case may be)" of the theory of reciprocal zonular action. "I want to make these new con- cepts understandable, which will stimulate discussion as well as scien- tific testing to confirm the validity of my theory," Dr. Goldberg said. "If the mechanism of accommodation is understood, we can move forward with this knowledge to help develop better accommodating IOLs." EW References 1. Goldberg DB. Computer-animated model of accommodation and theory of reciprocal zonular action. Clin Ophthalmol. 2011;5:1-7. 2. Lutjen-Drecoll E, Kaufman PL, Wasielewski R, Ting-Li L, Croft MA. Morphology and ac- commodative function of the vitreous zonule in human and monkey eyes. Invest Ophthal- mol Vis Sci. 2010;51:1554-1564. Editors' note: Dr. Goldberg has no financial interests related to this article. Contact information Goldberg: 732-219-9220, goldbergeye@gmail.com EW REFRACTIVE SURGERY November 2011 51 Figure 1. The Goldberg Model detailing the three elements of the posterior vitreous zonule Source: Daniel B. Goldberg, M.D.

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