Minimally Invasive Helical Implant for Intravitreal Drug Delivery

Abstract

Abstract: : Purpose: To investigate the feasibility of a helical implant for drug delivery and minimally invasive implantation into the posterior segment. Methods: Helical devices were coated with a triamcinolone acetonide impregnated polymer and incubated in vitro to simulate drug elution rate within the eye. Drug elution was quantified by HPLC and mass spectrophotometry. In addition, blank devices (without drug coating) were implanted into one eye of two pigmented rabbits. The animals were followed post–operatively by routine eye examination, photography, and electroretinography (ERG) for up to 3 months. Results: In vitro elution sampling was performed for up to 481 days. Devices eluting approximately 1.0 ug/day of steroid were found to exhibit near zero–order release kinetics over the followup period. Excellent correlation was obtained between the percent of drug released by weight and % released as detected using a UV/Vis spectrophotometer. The implantation procedure in rabbits was less than 10 minutes in duration. The small wire diameter of the device allowed for implantation through a 25 gauge self–starting "needlestick." The wound site was closed with a single conjunctival suture. In the 3 month the follow–up period, there was no sign of anterior or posterior segment inflammation. The conjunctiva over the scleral cap of the implant did not exhibit any inflammation or thinning. In both cases, there was sectorial lens opacification caused by contact with the device tip during implantation, owing to the relatively large size of the rabbit lens. The opacities remained stable throughout followup. Postmortem macroscopic examination of one eye, 3 months post–implantation, revealed that the vitreous was clear and the retina was normal. The conjunctival surface of the cap was covered by a thin capsule, while the intravitreal portion of the device remained free of fibrous tissue. ERG a–wave and b–wave latencies were within normal established limits at all followup times. Conclusions:A retrievable intravitreal device has been created that is capable of delivering therapeutic levels of corticosteroid for over one year. Implantation of this helical intravitreal device in rabbit eyes was simple and short in duration. Long term follow–up revealed excellent biocompatibility and lack of surgical complications.

Keywords: vitreoretinal surgery • corticosteroids • vitreous