Posterior dislocation of lens following Nd:YAG laser peripheral iridotomy in angle closure glaucoma

To report an uncommon and severe complication of Nd:YAG laser peripheral iridotomy (LPI) - spontaneous posterior dislocation of the crystalline lens into the vitreous cavity - in a patient with acute primary angle closure (APAC) glaucoma, and to discuss the underlying pathophysiology and preventive considerations. A single patient case report. Clinical records, slit-lamp examination findings, ophthalmic imaging, and operative notes were reviewed. A middle-aged male presented with primary angle closure (PAC) in the right eye (OD) with an intraocular pressure (IOP) of 28 mmHg and a Van Herick Grade I anterior chamber. Following poor medication compliance, he returned five days later with an acute pressure spike to 56 mmHg. He underwent Nd:YAG LPI with immediate IOP normalization. Eleven weeks post-LPI, he presented with sudden severe visual loss (count fingers at 50 cm). Examination revealed a complete posterior dislocation of the crystalline lens into the vitreous cavity. The eye underwent pars plana vitrectomy with lensectomy, achieving a final best-corrected visual acuity (BCVA) of 6/9 postoperatively. Posterior lens dislocation is a rare but devastating sequela of Nd:YAG LPI, particularly in eyes with pre-existing zonular compromise. The Patho mechanism is a two-hit model: latent zonulopathy from chronic angle closure, culminating in mechanical failure triggered by the laser shockwave -- amplified in very shallow anterior chambers. Clinicians should apply minimum effective energy, screen for zonular risk factors, and counsel patients explicitly about this low-frequency, high-impact complication.