An 18-year-old patient with Marfan syndrome has bilateral ectopia lentis with the lens subluxated inferiorly, causing significant monocular diplopia. The lens is still partially in the pupillary axis. Regarding the mechanism of lens subluxation in Marfan syndrome:

• A Weakness of the anterior capsule due to fibrillin-1 deficiency
• B Secondary to ciliary body atrophy reducing zonular tension
• C Deficiency of fibrillin-1 causing weakness of zonular fibers leading to zonular laxity ✓
• D Increased aqueous production causing hydrostatic pressure on zonules

Explanation

Marfan syndrome is caused by mutations in FBN1 gene encoding fibrillin-1, a major structural glycoprotein of microfibrils that form the core of elastic fibers. Zonular fibers (suspensory ligaments of the lens) are composed predominantly of fibrillin-1 microfibrils. Deficiency leads to weakened, poorly organized zonules that rupture under normal physiologic forces, causing characteristic superotemporal subluxation (in contrast to downward subluxation in homocystinuria). The lens capsule itself is structurally normal.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.