Introduction

Recently, there has been an increase in the use of therapeutic intraocular agents. Some of these agents are suspensions that are difficult to inject through small gauge needles, whereas others flow nicely through small gauge needles. Thirty-gauge needles are commonly used for injections of soluble agents because the smaller gauge causes less pain and tissue trauma. Recently, patients with diabetes have been using 31-gauge needles for insulin injections and blood glucose testing. We wish to describe the use of these needles for intravitreal injections (Figure 1a).

Figure 1
figure 1

(a) A comparison of a 30- and a 31-gauge needle showing the difference in size and thickness. (b) A comparison of a 30- and a 31-gauge needle inserted into an enucleated eye.

Full size image

Materials and methods

Eyes that were enucleated were photographed with both needles (Figure 1b). Ten patients undergoing injections of bevacizumab were injected with 31-gauge needles. The 31-gauge 5/8” (8 mm) needle comes attached to a 1 cm3 syringe (Becton-Dickinson Ultra-Fine II). The bevacizumab was transferred into the syringe by aspiration from the tip of another syringe that had been previously filled with an excess amount of drug, thereby not dulling the tip of the 31-gauge needle.

Patients who had undergone injections previously with the 30-gauge needles were asked their opinion as to whether this needle caused them less pain. The amount of reflux after the injection was qualitatively evaluated.

Results

Four patients had been previously injected with 30-gauge needles. All four patients rated the 31-gauge injection as less painful. The amount of reflux was markedly less.

Discussion

A 27-gauge needle, a 30- gauge needle, and a 31-gauge needle have diameters of 0.41 mm, 0.31 mm, and 0.26 mm, respectively (Figure 1b). The 31-gauge needles have become standard practice for patients with diabetes mellitus for daily blood glucose monitoring and insulin injection. Smaller gauge needles have increased acceptance in diabetic patients, because they cause less pain and less tissue trauma.1 The newer technology small gauge needles have a larger lumen and thinner wall resulting in 40% lower flow resistance than standard needle technology.2 Because of increasing use of recurrent intraocular injections in patients with retinal diseases, use of 31-gauge needles over the present 27- and 30-gauge needles may allow patients to have less discomfort and a higher acceptance of these recurrent injections.