Experimental investigation of needles, syringes and techniques for intravitreal injections

Background: To assess the techniques and materials used in intravitreal injections. Design: Descriptive study realized at the Vision Institute of the Federal University of São Paulo, Brazil. Samples: Different brands of needles and syringes, as well as enucleated porcine eyeballs. Methods: The ultra-structures of commonly used needles were analysed by scanning electron microscope, and they were compared using different criteria, such as irregularities and debris from the lubrication process. The scleral incision was also assessed using needles of different brands and sizes. Accuracies in drug administration were studied by comparing the residual and delivered volume of needles and also by the analysis of reflux after intravitreal injections. Main Outcome Measures: Efficiency and quality of materials used in intravitreal injections. Results: Ultra-structure analyses showed that all needles had different types of irregularities. Some photographs showed debris from the lubrication process, especially in BD needles. Scleral incision analysis showed a tendency of reducing the ocular damage with increasing gauge (P=0.024). The investigation of delivery accuracy showed that almost all needles underdosed the amount injected (P<0.05), and that the reflux could be minimized by tunnelled injections with thinner needles. Conclusion: Needles used in intravitreal injections possess many irregularities in their structures, which may cause different injection outcomes. Analyses of scleral incisions showed that the larger the needle gauge, the lesser the scleral damage and the risk of complications. Moreover, drug administration inaccuracies might be one of the causes for some unsuccessful attempts of treatment.