Pressure and Flow Characteristics of Ocular Viscoelastic and Silicone Oil Through Glaucoma Drainage Devices

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Russell Hampton
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1 Pressure and Flow Characteristics of Ocular Viscoelastic and Silicone Oil Through Glaucoma Drainage Devices Reid Mollman, MD Table Rock Regional Roundup 9/29/2017

2 Disclosures None of the participants in this project have a relevant financial relationship to disclose

3 Purpose To evaluate how intraocular Viscoelastic or Silicone Oil can alter the fluid dynamics of an Ahmed valve

4 Why is this important? Viscoelastic and Silicone Oil are frequently used intraoperatively in patients who have a glaucoma tube shunt in place. However, no data was found in the manufacturer s specifications, or in a literature search, to specify how these devices respond when subjected to infiltration by Viscoelastic or Silicone Oil.

5 Methods A laboratory setup was created to simulate intraocular conditions that the Ahmed valve would experience when subjected to silicone oil or ocular viscoelastic, and to measure the fluid dynamic response of the system when subjected to these conditions. To date, this study has been limited to Ahmed Valves

6 Experimental Setup Computer & Data Acquisition System Pressure transducer Water bath 98 Reservoir bottle Microfluidic Pump 2.5µL/min Ahmed Valve

7 Experimental Setup Components Reservoir Bottle Microfluidics Pump: A constant-flow pump used to simulate aqueous production by the ciliary body, set at a rate of 2.5µL/min, and meant to simulate nominal physiologic flow. Pressure transducer and data acquisition system Ahmed Valve: FP7 valve, which was new each run. Submerged in 1cm H20 at 98 to simulate in vivo conditions

8 Ahmed Valve

9 Methods Pressure and Flow characteristics were measured under three distinct trial conditions: Scenario #1: Non-primed Ahmed Valve Scenario #2: Primed Ahmed Valve, tubing filled with Silicone Oil Scenario #3: Primed Ahmed Valve, tubing filled with Viscoelastic Note: All of the above were ran with BSS flowing at 2.5µL/min

10 Pressure (mm Hg) Results Scenario #1 Non-primed Ahmed Valve with 2.5µL/min Run 1 Run 2 Run Time (Hours)

11 Pressure (mm Hg) Hg) Results Scenario Scenario #2: #2: Primed Ahmed Ahmed Valve with Valve BSS BSS 2.5µL/min with with Silicone Silicone Oil Oil in Ahmed in Ahmed Tube Tube lumen lumen Silicone Oil added Run 1 Run 2 Run 3 Run 1 Run 2 Run Silicone oil added Time 8 Time (Hours) (Hours)

12 Pressure (mm Hg) Results Scenario #3: Primed Ahmed Valve with 2.5µL/min with Viscoelastic in Ahmed Tube lumen Visco added Time (Hours) Run 1 - Viscoat Run 2 - Viscoat Run 3 - Provisc Viscoelastic Added

13 Discussion Points Why is there a large pressure spike when the Ahmed Valve is not primed? The silicone leaflets which function as the valve body are adherent to each other from the sterilization process, and a threshold pressure is needed to fully separate these plates for proper function. If this is not done, the steady state operating pressure in our trials was much higher (~40-50mmHg). Why do the pressure tracings show a sawtooth form? The Ahmed valve essentially functions as a nonlinear valve which requires a threshold pressure to open the plates, then closes at a lower pressure, then reopens once the threshold is again reached. What accounts for the increased resistance to flow in the Silicone Oil and Viscoelastic trials? A combination of higher viscosity materials flowing through the tube as well as these materials being cleared from the valve body leaflets. Water 1cP vs Silicone Oil 1,000cP vs Viscoelastic 40,000cP

14 Conclusions Lack of priming an Ahmed valve can raise the measured peak pressure of the system even higher (>200mmHg) than primed Ahmed valves which were infiltrated with Viscoelastic or Silicone Oil. Also, non-primed valves appeared to have far more erratic and higher steady-state pressures. This illustrates the critical importance of priming the valve prior to implantation. Viscoelastic or silicone oil can both substantially increase the measured peak pressure at a given flow rate. The pressure does not always return to baseline after the viscoelastic or silicone oil is cleared from the system, and the downtrend back to baseline primed pressures can take several hours. The OVDs were found to yield far higher measured peak pressures than SO. Silicone Oil peak ~30-40mmHg Provisc >80mmHg Viscoat >160mmHg

15 Primary Limitations The experimental setup is a model, it is not a study of the performance of the implants in human subjects The analysis was limited to only the Ahmed Valve system, it was not able to account for alternate aqueous drainage pathways found in vivo Aqueous production was simulated by a constant flow pump at 2.5µL/min, whereas aqueous production is variable based on ciliary body function which can be affected by surgery, inflammation, etc. The analysis was over a 24hr period, or less Only three runs were completed for each of the trial scenarios

16 Special Thanks to: Dr Paul Munden, MD Dr Michelle Boyce, MD Tabitha Teo Sara Wilson Ronald Dougherty

17 Questions

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