Experimental study of occlusion break surge volume in 3 different phacoemulsification systems.

PURPOSE: To evaluate surge volume after occlusion breaks in 3 different phacoemulsification systems. SETTING: Alcon Research LLC, Lake Forest, California. DESIGN: Experimental study. METHODS: A mechanical spring eye model was used to test the Centurion with Active Sentry, WhiteStar Signature Pro, and Stellaris PC. Raw oscilloscope data were converted to volumetric and pressure measurements. Fitted average surge traces were generated for each test condition and used to develop an interpolation algorithm to predict transient occlusion break surge events. Two-dimensional heat maps were generated. RESULTS: During occlusion break surge, the Centurion with Active Sentry had smaller aqueous volume losses than the WhiteStar or Stellaris PC. Maximum surge volumes within the mechanical spring eye model displacement limit were 74.7 µL, 157.5 µL, and 151.7 µL using Centurion with Active Sentry, WhiteStar, and Stellaris PC, respectively. In the aphakic state, heat maps showed that Centurion with Active Sentry had less than 20% aqueous volume loss across all vacuum limits and target intraocular pressure; WhiteStar and Stellaris PC systems had up to 35% and 50% aqueous volume losses, respectively, at the higher vacuum limits. In the phakic state, Centurion with Active Sentry had up to 30% aqueous volume loss and WhiteStar and Stellaris PC systems had up to 50% aqueous volume losses. In addition, predicted transient traces demonstrated that Centurion with Active Sentry had the lowest percentage simulated aqueous volume loss compared with WhiteStar or Stellaris PC. CONCLUSIONS: Centurion with Active Sentry had lower aqueous volume losses after occlusion break than WhiteStar and Stellaris PC systems at all surgical settings.

Mechanical model of human eye compliance for volumetric occlusion break surge measurements.

PURPOSE: To develop a mechanical model of human eye compliance for volumetric studies. SETTING: Alcon Research, Ltd., Lake Forest, California, USA. DESIGN: Experimental study. METHODS: Enucleated human eyes underwent pressurization and depressurization cycles with peak intraocular pressures (IOPs) of 60 to 100 mm Hg; anterior chamber pressure and volume changes were measured. Average net volume change curves were calculated as a function of IOP for each eye. Overall mean volumes were computed from each eye's average results at pressure points extrapolated over the range of 5 to 90 mm Hg. A 2-term exponential function was fit to these results. A fluid chamber with a displaceable piston was created as a mechanical model of this equation. A laser confocal displacement meter was used to measure piston displacement. A test bed incorporated the mechanical model with a mounted phacoemulsification probe and allowed for simulated occlusion breaks. Surge volume was calculated from piston displacement. RESULTS: An exponential function, V = C1 × exp(C2 × IOP) + C3 × exp(C4 × IOP) - V0, where V, the volume, was fit to the final depressurization curve obtained from 15 enucleated human eyes. The C1 through C4 values were -0.07141, -0.23055, -0.14972, and -0.02006, respectively. The equation was modeled using a piston system with 3 parallel springs that engaged serially. The mechanical model mimicked depressurization curves observed in human cadaver eyes. CONCLUSION: The resulting mechanical compliance model measured ocular volumetric changes and thus would be helpful in characterizing the postocclusion break surge response.

Aqueous volume loss associated with occlusion break surge in phacoemulsifiers from 4 different manufacturers.

PURPOSE: To evaluate aqueous volume losses associated with occlusion breaks at varying vacuum limits in phacoemulsification systems from 4 different manufacturers. SETTING: Alcon Research Ltd., Lake Forest, California, USA. DESIGN: Experimental study. METHODS: The anterior chamber was modeled using the spring eye model. Systems tested included the Centurion, Whitestar Signature, Stellaris PC, and EVA. Occlusion breaks were actuated at vacuum limits of 200, 300, 400, 500, and 600 mm Hg and a target intraocular pressure of 55 mm Hg. RESULTS: The model eye piston reached its measurement limit just below 600 mm Hg on the EVA and just above 400 mm Hg on the Stellaris PC. Higher vacuum limits could not be tested on these 2 units. Surge volumes varied from 17 to 77 µL on the Centurion, 30 to 103 µL on the Whitestar Signature, 67 µL to 163 µL on the Stellaris PC, and 47 to 165 µL on the EVA. Assuming an average phakic eye aqueous volume of 250 µL, these µL values correspond to percent aqueous volume losses of 7% to 31% on the Centurion, 12% to 41% on the Whitestar Signature, 27% to 65% on the Stellaris PC, and 19% to 66% on the EVA. Surge responses increased on all machines with each increment in vacuum limit. The Centurion had the lowest surge volumes across all vacuum limits. CONCLUSIONS: Occlusion break surge volumes vary considerably across phacoemulsification platforms. Severe chamber shallowing might occur if an occlusion break occurs under high vacuum on some systems.

Phacoemulsifier occlusion break surge volume reduction.

PURPOSE: To compare the volumetric occlusion break surge responses of phacoemulsification units from 1 company over 3 generations under varying vacuum limits and target intraocular pressure (IOP) settings. SETTING: Alcon Research, Ltd., Lake Forest, California, USA. DESIGN: Experimental study. METHODS: Three generations of phacoemulsification units (Infiniti Vision System, Centurion Vision System, and Centurion Vision System with Active Sentry upgrades) were tested. Volumetric surge responses were measured after occlusion breaks at vacuum limits of 200 mm Hg, 300 mm Hg, 400 mm Hg, 500 mm Hg, and 600 mm Hg and target IOPs of 30 mm Hg, 55 mm Hg, and 80 mm Hg. An acrylic test chamber with a piston attached to 3 springs modeled the human eye in this study. The springs were calibrated to mimic volumetric changes in the eye over a wide range of IOPs. RESULTS: Occlusion break surge volumes varied from 17.4 µL to 153 µL, corresponding to 7% and 61%, respectively, of the aqueous volume in the average phakic eye and to 4% and 33% of the aqueous volume in the average aphakic eye. CONCLUSION: Occlusion break surge volumes decreased with increasing target IOP, decreasing vacuum limit, and each generational increment in the phacoemulsification system.