Dependence of blood flow velocity in the central retinal artery on intraocular pressure during phacoemulsification with active fluidics

BACKGROUND: Irrigation during phacoemulsification is associated by a rapid increase in intraocular pressure. The difference of the active fluidics system from the passive one is its ability to maintain the set intraocular pressure throughout the entire procedure. The effect of a rapid intraocular pressure increase on retinal hemodynamics during surgery remains poorly understood. AIM: The work aimed to study intraoperative changes in blood flow parameters in the central retinal artery during phacoemulsification with different intraocular pressure preset in the phacoemulsification system. METHODS: A total of 11 patients with early stage cataract (Pentacam Nucleus Staging: 1–2) without cardiovascular comorbidities were examined. The mean age of the patients was 68 ± 8.4 years. All patients underwent ultrasound phacoemulsification using Centurion Vision System (Alcon, USA) with active fluidics. The intraocular pressure was measured using iCare Pro tonometer. Blood flow in the central retinal artery was assessed using a GE Logiq S8 multi-purpose ultrasound system. Blood pressure at the brachial artery was measured using Draeger Vista 120. The following parameters were assessed: statistical significance (the paired t-test) of the intraocular pressure differences at three time points (before surgery, at 40 and 60 mmHg as set in the phacoemulsification system); changes in peak systolic velocity and end-diastolic velocity at the initial and control time points of 40 and 60 mmHg; their dependence on the intraocular pressure increase; the effect of mean blood pressure on peak systolic velocity and end-diastolic velocity at control time points using linear regression analysis; and the correlation of their changes at each control time point (the Spearman correlation test). RESULTS: Mean intraocular pressure values at three time points were 20.82±3.8, 36.9±4.0, and 62.8±3.3 mmHg, respectively. At 40 mmHg control point, mean peak systolic and end-diastolic velocities were 12.0±3.9 and 3.3±1.2 cm/s, respectively. At 60 mmHg control point, mean peak systolic velocity decreased to 10.2±3.6 cm/s. End-diastolic velocity significantly decreased to an average of 1.1±1.1 cm/s, and diastolic blood flow was not recorded in 3 cases. At 60 mmHg control point, a statistically significant decrease in end-diastolic velocity was noted vs. the pre-operative value (p 0.008), and peak systolic velocity also decreased (p=0.05). Significant effect of mean blood pressure on changes in blood flow velocity was not reported. A negative correlation was found between the change in resistive index and mean blood pressure at 40 and 60 mmHg control points (p 0.05). CONCLUSION: An intraoperative intraocular pressure increase may significantly decrease peak systolic velocity and end-diastolic velocity in the central retinal artery and result in retinal blood flow deficiency. To maintain stable hemodynamics in retinal vessels during phacoemulsification, intraocular pressure should not exceed a specific threshold, which was 40 mmHg in our study.