2020–2021 BCSC Basic and Clinical Science Course™
2 Fundamentals and Principles of Ophthalmology
Part I: Anatomy
Chapter 2: The Eye
The lens is held in place by the system of zonular fibers (zonule, suspensory ligament) that originate from the basal laminae of the nonpigmented epithelium of the pars plana and pars plicata of the ciliary body. These fibers attach chiefly to the lens capsule anterior and posterior to the equator (Fig 2-30). Each zonular fiber is made up of multiple filaments of fibrillin that merge with the equatorial lens capsule. In Marfan syndrome, mutations in the fibrillin gene lead to weakening of the zonular fibers and subluxation of the lens.
When the eye is focused for distance, the zonule is under tension and the lens form is relatively flattened. During accommodation, contraction of the ciliary muscle moves the proximal attachment of the zonule forward and inward, so the lens becomes more globular and the eye adjusts for near vision (Video 2-2).
Figure 2-30 Zonular fibers. The zonular fibers insert into the lens capsule anterior and posterior to the equator. Note the ciliary processes between the zonular fibers.
(Courtesy of John Marshall.)
Computer model of accommodation.
Courtesy of Daniel B. Goldberg, MD.
Bourge JL, Robert AM, Robert L, Renard G. Zonular fibers, multimolecular composition as related to function (elasticity) and pathology. Pathol Biol (Paris). 2007;55(7):347–359.
Goldberg DB. Computer-animated model of accommodation and presbyopia. J Cataract Refract Surg. 2015;41(2):437–445.
Streeten BW. Anatomy of the zonular apparatus. In: Duane TD, Jaeger EA, eds. Biomedical Foundations of Ophthalmology. Philadelphia: Harper & Row; 1992.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.