The intravitreal injection pain study: a randomized control study comparing subjective pain with injection technique

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Increasing numbers of people require prolonged intravitreal anti-vascular endothelial growth factor (anti-VEGF) for retinal conditions (Stewart 2012), but the most effective peri-procedural analgesia is uncertain (Shiroma et al. 2017). We compared the efficacy of two popular techniques, subconjunctival injection (SCI) with 2% lignocaine and topical pledget (TP) with 0.5% amethocaine hydrochloride, through a prospective, randomized control trial. We consented all adult patients undergoing anti-VEGF injections, prospectively over 12 weeks in 2014 at one tertiary centre hospital in Australia (n = 112). Research staff used block randomization, participants were not told of their allocated anaesthetic and the treating medical team was only aware on the day of treatment. All patients underwent a standardized approach to minimize confounders: two drops of 0.5% amethocaine hydrochloride, 1 drop of 5% povidone–iodine after 2 min, positioning of an eyelid speculum, the allocated anaesthetic technique and injection of similar volumes of anti-VEGF, irrigation with 0.9% normal saline, and no antibiotics, eye pads or other pain relief. In the SCI group, 0.2 ml of 2% lignocaine was injected with a 30G needle as a subconjunctival bleb in the superior temporal region of the eye, followed by sterile precautions for 2 min and then anti-VEGF injection. In the TP group, a cotton bud soaked in 0.5% amethocaine hydrochloride was applied to the superior temporal region for 30 s followed immediately by anti-VEGF injection. Pain scores on a visual analogue scale (VAS) from 0 to 10 were recorded at 5 min and 24 hr postinjection over the phone using the same VAS. Sixty-seven patients returned and underwent the opposite anaesthetic technique (SCI; n = 36, TP; n = 31). Patient withdrawal from the study, not requiring an additional injection within the study period and failure to attend appointments, limited studying the rest of the cohort. Pain scores at 5 min, 24 hr and patient preferences were collected. There were no differences in baseline characteristics that could introduce bias between comparative groups (age, sex, previous number of injections, type of anti-VEGF, reason for injection and injector). The median pain score at 5 min for the SCI group of 1.0 (range: 0–8.0) was lower than the TP pain score of 2.5 (range: 0–8.0; p = 0.003, Mann–Whitney U-test). Figure 1 shows the distribution of pain scores. In those who underwent the opposite anaesthetic technique, the median pain score at 5 min for the SCI group of 1.0 (range: 0–5) was lower than the TP pain score of 3.0 (range: 0–8; p = 0.001). No difference in pain scores was found at 24-hr postinjection; however, 75% of participants who had both techniques preferred SCI. We recognize that the subjective nature of pain makes comparisons difficult (Rosier et al. 2002). In the patients who were examined again, awareness of being administered the alternate anaesthetic could have caused biases in pain scores. Clinic limitations prevented the use of a sole injector. The majority of patients were administered bevacizumab. Participants could not be truly blinded as SCI is an extra injection. As patients were not re-examined at 24 hr, other complications such as subconjunctival haemorrhage were not recorded. Compared to previous studies, a systematic review concluded that there is no sufficient evidence comparing the different anaesthetic techniques and a formal meta-analysis was not possible due to study heterogeneity, but a SCI of 2% lignocaine could be a better option for highly pain-sensitive patients (Shiroma et al. 2017). This study suggests that SCI may be a better option than TP anaesthetic for intravitreal injections given lower pain scores and patient preference. Recent trials support the use of topical nepafenac or apraclonidine in addition to SCI and TP anaesthesia that may further reduce pain scores and ensure a comfortable experience for patients (Ulrich 2014; Lagstein et al. 2017).

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