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Vitreous traction after Ozurdex injection.

Dear Editor: We read with great interest the article by Bakri and Omar describing the formation of a vitreomacular traction after an uneventful intravitreal Ozurdex injection. We can confirm this rare clinical event, as we observed the onset and formation of a macular hole 12 days after an uneventful Ozurdex injection (Fig. 1). We suggest that the cause of macular hole formation is rooted in the transient injection dynamics and that the macular hole appeared immediately after the implantation. Presumably, the patient did not realize it himself as visual acuity was only 0.05 before injection. The first optical coherence tomography-based control examination was performed 12 days after ozurdex implantation when the macular hole was detected for the first time. The formation of macular holes result from tangential traction at the posterior pole in eyes with firm vitreoretinal adhesions. A sudden traction on the vitreous, as frequently seen during sudden vacuum aspiration before laser-assisted in situ keratomileusis or YAG-capsulotomy, may increase tractional shear forces on the vitreomacular surface, inducing the formation of a macular hole. Bertelmann et al. have recently determined a high incidence of vitreoretinal adhesions in eyes with retinal vein occlusion compared to an age-matched group. About 72% of patients aged 65–69 presented an attached posterior vitreous in healthy eyes compared with 100% in central retinal vein occlusion, and 89% in branch retinal vein occlusion. The reported development of a vitreomacular traction after an Ozurdex injection in an eye with central retinal vein occlusion (CRVO) may indicate that the velocity during the application could cause drag force on the vitreous gel, inducing vitreoretinal traction at the posterior pole. In an experimental study with a high-speed camera, Meyer et al. measured the muzzle velocity during the application of Ozurdex implants and confirmed its high initial velocity. High-speed real-time recordings revealed that the entire movement of the dexamethason (DEX)-implant lasted between 28 and 55 ms in water (group A; n = 7) and 1–7 ms in vitreous (group B; n = 7) filled tanks. The implants moved with a mean muzzle velocity of 820 – 350 mm/s [ – standard deviation (SD), range 326–1349 mm/s] in group A and 817 – 307 mm/s ( – SD, range 373–1185 mm/s) in group B. In both groups, the implant gradually decelerated due to drag force. With greater distances, the velocity of the DEX-implant decreased exponentially to a complete stop at 13.9–24.7 mm in group A and at 6.4–8.0 mm in group B. Five DEX-implants in group A reached a total distance of more than 15 mm and their calculated mean velocity at a retinal impact of 15 mm was 408 – 145 mm/s ( – SD, range 322–667 mm/s) and the consecutive normalized energy was 0.55 – 0.44 J/m ( – SD). In group B, none of DEX-implants reached a total distance of 15 mm or more. The muzzle velocity of the DEX-implant of*0.8 m/s decreases exponentially over distance. The measured drag force decreases faster in vitreous than in water. The impact energy of the implant on the projected retinal area does not reach reported damage levels as for foreign bodies or other projectiles. The measurements indicate that the application is safe and that the directly applied energy of the implant does not induce any damage to the retinal surface. However, the initial high velocity of the implant entering the vitreous