Randomised Controlled Trial: Influence of Subconjunctival Anaesthesia Duration on Pain Perception During Intravitreal Injections.

Background: The intravitreal injection (IVI) is one of the most performed vitreoretinal procedures in ophthalmology. Subconjunctival anaesthesia (SCA) with 2% lidocaine is a commonly used modality to reduce procedural pain and patient distress. Currently, there is no unifying recommended wait time between SCA and IVI. The purpose of this study is to determine the optimal wait time between the two, whilst maintaining clinical efficiency.

Methods: Single-blinded randomised clinical trial. Two hundred and forty patients were randomly assigned to one of four groups: wait time of 2, 3, 4 or 5 min. The primary outcome was pain level graded by the patient on a 10-point visual analogue scale. The secondary outcome was the willingness to receive further IVI with the current pain level. Data points were collected on patient demographics and characteristics.

Results: The mean pain scores showed a decreasing trend with increasing wait times, 2.27 (2 min), 1.03 (3 min), 0.67 (4 min) and 0.58 (5 min). More patients were willing to receive further IVI with increasing wait times, 92% (2 min), 97% (3 and 4 min), and 100% (5 min). These differences were statistically significant at each time interval.

Conclusion: Longer wait times post-SCA were associated with better anaesthetic effect and higher patient acceptance to continue receiving IVI. The most marked difference was observed between 2- and 3-min groups. Based on our findings, a minimum wait time of 3 min should be recommended as the group had reported acceptably low pain scores (1.03) while maintaining high patient satisfaction (97%).