Sodium Fluorescein as an Optical Label to Evaluate Subretinal Injection

There is renewed interest in subretinal drug delivery as the result of novel and emerging treatments for retinal diseases, including retinal gene therapy. However, our knowledge of the distribution of subretinally delivered drugs is incomplete; herein, we describe a qualitative and quantitative means of surveying the early intraocular distribution of subretinally delivered drugs using dilute sodium fluorescein (NaFl). METHODS: Sodium fluorescein 10% was serially diluted and mixed with a solution containing tissue plasminogen activator (tPA) at a final concentration of 0.1 mg/mL NaFl and 0.5 mg/mL of tPA. Because this solution was to be used in the context of subretinal tPA injection in the treatment of subretinal hemorrhage, fluorophotometry with, and without, the presence of human whole blood was performed to derive a formula to calculate the concentration of NaFl based on the fluorescence of aspirated intraocular fluid. Videos of subretinal tissue plasminogen activator surgery in a case are presented as a qualitative demonstration of the technique and vitreous cavity fluid collected at case completion underwent fluorophotometry to estimate the loss of therapeutic solution. RESULTS: Although the presence of hemoglobin in blood suppresses fluorescence of NaFl, we demonstrate that centrifuging admixtures of blood with NaFl negates the optical effects of blood and yields identical fluorescence versus concentration plots to those of NaFl solution alone. We also demonstrate that NaFl at 0.1 mg/mL can be readily used to qualitatively assess drug losses before, during, and after subretinal injection. Furthermore, we describe how it may be used to quantitatively estimate the total loss of therapeutic solution during subretinal injection using fluorophotometry on aspirated fluid from the vitreous cavity (loss estimated as 4% in the case presented). CONCLUSION: Sodium fluorescein at a concentration of 0.1 mg/mL can be used to quantitatively and qualitatively assess the fate of subretinally injected drugs during subretinal injection surgery.