Routes for Drug Delivery to the Eye and Retina: Intravitreal Injections

The advantage of intravitreal injections is an immediate and increased therapeutic effect in the intended retinal tissue. The accuracy, precision and reproducibility of the delivered volume depend on the size of the syringe and the physician's manual experience. The eyelids and eyelashes are usually disinfected using a povidone-iodine solution (10%); a sterile speculum is placed and drops of povidone-iodine (5%) are applied. The use of adequate anesthetic topical lidocaine 2% is required. The injection site should be located 3.5-4 mm posterior to the limbus. The angle of the incision through the sclera may be directed in an oblique fashion of 30°. The diameter of the needle should be smaller than 25 G, and the injected volume should be limited to 0.15 ml without a routine paracentesis. The incidence of lens injury is 0.006% (2/32,318) and 0.013% (5/35,942) for rhegmatogenous retinal detachments. The rate of suspected endophthalmitis is 0.018% after bevacizumab and 0.027% after ranibizumab injections. Sterile inflammations have been observed after Avastin injections. The concentrations of vascular endothelial growth factor inhibitors decline in a monoexponential fashion. The half-life of unbound bevacizumab is 9.82 days and that of ranibizumab 7.19 days.