Purpose:
Intraocular pressure (IOP) and aspiration flow rates are two important parameters during vitreoretinal surgery. Intraoperative hypotony has been associated with choroidal detachment and suprachoroidal hemorrhage. Limited flow has been deemed unsuitable for procedures involving removal of thick fibrous tissue or dense hemorrhages while restricting flow rates during procedures involving delicate tissues is thought to improve safety. The present study investigates the relationship between IOP and flow rates during simulated vitrectomy with high cut rate vitrectomy probes and compares its performance to the existing 5000 cpm paradigm.
Methods:
Using the CONSTELLATION® Vision System (Alcon), balanced salt solution (BSS® Irrigating Solution) was infused at 30mmHg in a closed globe model eye. A flow sensor in-line with the infusion tubing and a pressure transducer attached to the model eye globe measured the flow rate and changes in IOP, respectively, over a range of cut rates (500 cpm - 7500 cpm), 3 vacuum levels (250mmHg, 450mmHg, 650mmHg) and 3 duty cycle modes (core-biased open, shave-biased closed and 50/50). Data was collected for two probes for each gauge under investigation (23G & 25G+™).
Results:
In the "core" duty cycle mode, IOP increased while flow rates decreased with increasing cut rates while in the "shave" mode the opposite trend was observed matching the known trend of biased open and biased closed duty cycle modes. Table 1 lists the IOP and flow rates at the maximum vacuum level for 25G+™ high cut rate probes (7500cpm) and compares it to lower cut rate probes (5000cpm).
Conclusions:
With the high cut rate vitrectomy probes, cut rates greater than 5000 cpm can be employed. Higher flow rates were observed for the high cut rate vitrectomy probes compared to 5000 cpm probes while IOP stability was maintained across the range of cut rates tested.
Keywords: vitreoretinal surgery • intraocular pressure