EyeWorld India March 2012 Issue

37 EW REFRACTIVE March 2012 Figure 1. The Goldberg Model detailing the three elements of the posterior vitreous zonule Source: Daniel B. Goldberg, MD A new theory of accommodation is proposed A lthough most ophthalmologists accept Helmholtz’s lenticular theory of accommodation, there is continuing debate and controversy over the role of the extralenticular elements in accommodation including the vitreous and zonule. Understanding the zonular anatomy and its relationship to the anterior hyaloid and ciliary body has been elusive. However, a new theory proposed by Daniel B. Goldberg, MD , uses computer animation to provide a consolidated theory of the mechanism of accommodation 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, Pa., USA, and a founding partner, Atlantic Eye Physicians, Little Silver, NJ, USA. He has also developed a website (www. goldbergtheory.com) to explain his theory in hopes it will lead to better accommodating IOL development. “The computer-generated model supports the concept that the ciliary body/zonule/ anterior hyaloid complex contributes to the changes in the posterior lens capsule during accommodation,” he told EyeWorld. Another theory, one that debates 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 pressure,” Dr. Goldberg said. However, a paper published by Croft et al. last year 2 used improved scanning electron microscopy and ultrasonic biomicroscopy 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 verification 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 validate 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 contraction are distributed in shaping the lens during accommodation and disaccommodation”; the three- dimensional architecture of the zonules was first studied in the late 1970s. The Croft study described a “cleft” between the vitreous membrane and the pars plana zonules bridged by zonular fiber bundles those researchers called the intermediate 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 multilayered, interconnected sponge-like ring where the vitreous attaches to the posterior pars plana and ora serrata region”, Dr. Goldberg said (see Figure 1). The animated model of accommodation enables a new perspective and framework to demonstrate and interpret the mechanism of accommodation. “The engine of accommodation is the contraction of the ciliary body mediated by the distribution of forces via all elements of the zonular apparatus,” Dr. Goldberg said. “The resulting changes in refraction are due to the increased thickness of the lens and the increased curvature of the anterior and posterior capsule. The complex anatomy of the vitreous zonule results in traction on the vitreous membrane peripherally.” During accommodation, the ciliary body moves both forward and centripetally, and the posterior zonular attachments simultaneously stretch, affecting the shape changes in the lens. During disaccommodation, 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 contraction, the anterior zonules lose tension, while the posterior zonules stretch and exert force on the posterior 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 Reciprocal zonular action by Michelle Dalton EyeWorld Contributing Editor tension 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)” on the theory of reciprocal zonular action. “I want to make these new concepts understandable, which will stimulate discussion as well as scientific 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 accommodative function of the vitreous zonule in human and monkey eyes. Invest Ophthalmol Vis Sci. 2010;51:1554-1564 Editors’ note: Dr. Goldberg has no financial interest related to this article. Contact information Goldberg: 732-219-9220, goldbergeye@gmail.com