Comparative analysis of iris blood flow after first-eye and second-eye cataract surgeries: insights into increased pain perception in the second eye.

Objective: To investigate quantitative changes in iris blood flow after first-eye and second-eye cataract surgeries, and their correlation with increased pain in the second eye.

Methods and analysis: In this prospective study, 88 eyes of 44 participants who underwent uneventful cataract surgery were followed up at enrolment, 1 day before, and 1 day, 1 week and 1 month after each eye surgery. Iris blood flow was quantified by a swept-source optical coherence tomography angiography and intraoperative pain was evaluated. Participants were divided into three groups according to time intervals between two eye surgeries: ≥1 to <2 weeks (short interval), ≥2 to ≤4 weeks (medium interval) and greater than 4 weeks (long interval).

Results: The second eye experienced two significant increases in iris blood flow following cataract surgery: one after the first eye and the other after its own, with the latter being significantly higher than the increase observed in the operated eye after the first surgery (p<0.05). Additionally, the second eye showed higher iris blood flow density in the short interval group compared with the long and medium at specific time points (p<0.05). The bilateral pain index difference positively correlated with second eye iris blood flow density (p<0.05) and was significantly greater in the short interval group than the long interval group (p<0.05).

Conclusions: Iris blood flow increased in the second-operated eye post surgery compared with the first eye, which may correlate to second-eye pain. However, due to the variability in individual pain perception, a larger sample size is needed to prospectively validate our findings to improve their generalisability.

Trial registration number: NCT02182921.