Updated computer-animated model elevates understanding of accommodation, presbyopia

Take-home:

A new version of a model of the mechanism of accommodation-showing how anatomic structures interconnect-enhances understanding of zonular architecture.

By Nancy Groves; Reviewed by Daniel B. Goldberg, MD, FACS

Philadelphia-Aided by an updated version of a computer-animated model of the mechanism of accommodation (CAMA 2.0), Daniel B. Goldberg, MD, FACS, has proposed a new classification of zonular architecture based on structure and function.

In case you missed it: Combined refractive lenticule extraction + CXL promising

Dr. Goldberg, clinical associate professor of ophthalmology, Drexel College of Medicine, Philadelphia, introduced his first computer-animated model of accommodation in 2011 and presented the new version earlier this year. The model-based on anatomy, biometry, endoscopy, and video ultrabiomicroscopy-represents a biometrically accurate model of a 25-year-old eye with 8 D of accommodation.

Motivating factor

The driving force of this work over the past 5 years has been to find a cure for presbyopia, a goal that first motivated Dr. Goldberg to work on an improved accommodating IOL.

While studying the mechanics involved, Dr. Goldberg said he realized that the function of the zonules in accommodating the lens was poorly understood. The more he learned about the network of fibers, the more he grasped that words and pictures were inadequate to explain the new anatomical findings. Dr. Goldberg said he concentrated instead on creating an animated model of the elements of the zonules and the movements of the extralenticular tissues.

Figure 1. CAMA 2.0 composite model showing the eye in accommodation (right half) and disaccommodation (left half).

NEXT: Continued + Video

“It puts together all of the structures at once, moving synchronously,” said Dr. Goldberg, also founding partner and refractive surgeon/director, Atlantic Eye Physicians, Little Silver, NJ.

In case you missed it: Overcoming challenges of cataract surgery in Marfans syndrome

“Prior investigators and theorists were always trying to imagine what was happening, but they had no real way of visualizing it,” he said. “If you look at earlier drawings of the zonules, they’re very primitive compared with where we are now with this computer model.”

The concept of the first CAMA, using model-based reasoning, was that during ciliary body contraction, the anterior zonules lose tension while the posterior zonules stretch. During ciliary body relaxation, the posterior zonules lose tension as the lens flattens and is pulled back by the increasing tension of the anterior zonules. Dr. Goldberg described this process in a 2011 study (Goldberg DB. Clin Ophthalmol. 2011:1559-1566).

NEXT: What's new

What’s new

The updated model is a visual presentation that incorporates all the anatomic structures in order to show how they interconnect and function as a unit, Dr. Goldberg said. It shows the anterior, posterior, and intermediate vitreous zonules, a pars plana zonule, and a newly described posterior insertion zone to lens equator zonule (PIZ-LE zonule). The key points of the new model were recently summarized (Goldberg DB. Cataract & Refractive Surgery Today Europe, April 2014).

Figure 2. The anterior zonules release tension on the lens during accommodation, allowing the intrinsic elasticity of the lens to round-up the lens, contributing to the increase in lens thickness and steepening of the anterior and posterior capsules.

Figure 3. The crossing zonules cradle, shape, and stabilize the posterior lens and anterior vitreous membrane. The anterior vitreous zonule (yellow) is shown inserting into Weiger ligament, and the PIZ-LE zonule (purple) is shown anchoring the lens equator to the posterior insertion zone.

As demonstrated in CAMA 2.0, the anterior zonules release tension on the lens during accommodation, and the lens elasticity rounds the lens, contributing to increases in thickness and steepening of the anterior and posterior capsules. Then, during disaccommodation, the anterior zonule increases tension, which flattens the lens.

The crossing zonules cradle, shape, and stabilize the posterior lens. In the model, the anterior vitreous zonule is inserted in the Weiger ligament, and the PIZ-LE zonule anchors the lens equator to the posterior insertion zone. The crossing zonules and Weiger ligament maintain lens placement while the anterior and posterior zonules provide reciprocal accommodation and disaccommodation.

NEXT: Looking ahead

The third functional group that Dr. Goldberg identified is the posterior zonules, which include the intermediate vitreous zonule, posterior vitreous zonule, and pars plana zonule. He described these as reciprocal tension fibers that follow ciliary muscle movement and are anchored in the elastic choroid.

Figure 4. The posterior zonules, which include the intermediate vitreous zonule (red), the posterior vitreous zonule (off-white), and the pars plana zonule (green).

Looking ahead

Dr. Goldberg is already considering new avenues of research on accommodation, but said the main goal at this time is sharing the model and the information he and others have learned so far.

“My hope is that this can be available to everybody in the visual sciences, because it’s a dramatic change in the understanding that you can have about accommodation,” he said.

He also credits a group of European and American investigators whose research on anatomy and accommodative movements he has drawn upon to prepare his models. They include Elke Lutjen-Drecoll, MD, and colleagues at the Institute of Anatomy in Erlangen, Germany, as well as Mary Ann Croft, MS, and Paul Kaufman, MD, and colleagues at the National Primate Lab and the University of Wisconsin in Madison.

Daniel B. Goldberg, MD, FACS

E: goldbergeye@gmail.com

Dr. Goldberg is a consultant to Ace Vision and Bausch + Lomb.