Purpose
To determine capsular breakage risk from contact by phacoemulsification needles by machine and tip type.
Design
Experimental laboratory investigation.
Methods
Infiniti (Alcon, Inc.) with Intrepid cartridges and Signature (Abbott Medical Optics, Inc.) phacoemulsification machines were tested using 19- and 20-gauge sharp and rounded tips. Actual and unoccluded flow vacuum were determined at 550 mm Hg, bottle height of 75 cm, and machine-indicated flow rate of 60 mL/minute. Breakage from brief tip contact with a capsular surrogate and human cadaveric lenses was calculated.
Results
Nineteen-gauge tips had more flow and less unoccluded flow vacuum than 20-gauge tips for both machines, with highest unoccluded flow vacuum in the Infiniti. The 19-gauge sharp tip was more likely than the 20-gauge sharp tip to cause surrogate breakage for Signature with micropulse and Ellips (Abbott Medical Optics, Inc.) ultrasound at 100% power. For Infiniti using OZil (Alcon, Inc.) ultrasound, 20-gauge sharp tips were more likely than 19-gauge sharp tips to break the membrane. For cadaveric lenses, using rounded 20-gauge tips at 100% power, breakage rates were micropulse (2.3%), Ellips (2.3%), OZil (5.3%). Breakage rates for sharp 20-gauge Ellips tips were higher than for rounded tips.
Conclusions
Factors influencing capsular breakage may include active vacuum at the tip, flow rate, needle gauge, and sharpness. Nineteen-gauge sharp tips were more likely than 20-gauge tips to cause breakage in lower vacuum methods. For higher-vacuum methods, breakage is more likely with 20-gauge than with 19-gauge tips. Rounded-edge tips are less likely than sharp-edged tips to cause breakage.
Capsular breakage is one of the more common complications in association with phacoemulsification and cataract extraction, with a reported incidence of between 1.7% and 5.2%. Although the results after capsular breakage have been reported as generally good, clearly there is an increased incidence of cystoid macular edema, potential posterior loss of nuclear fragments resulting in the need for additional surgery, intraocular lens decentration, increased intraocular pressure, retinal detachment, and endophthalmitis. For this reason, much of phacoemulsification technique and technology has centered around improving the safety of the procedure to minimize the possibility of capsular breakage during cataract surgery.
The inadvertent contact of the phacoemulsification needle to the capsule, when it does occur, is a major cause of capsular breakage. However, little has been written regarding the risk of capsular breakage and the influence of various factors such as needle configuration and ultrasound type used. This study looks specifically at the risk of capsular breakage if the capsule were contacted inadvertently by the phacoemulsification needle during cataract surgery.
Methods
Contact With a Capsule Substitute
Plastic wrap (Reynolds Seal-Tight Plastic Wrap; Alcoa, Inc., Richmond, Virginia, USA) was stretched tightly around 1 end of an open 4-inch diameter polyvinyl chloride tube as a surrogate for the capsule. The 2 phacoemulsification machines tested were the Infiniti (Alcon, Inc., Fort Worth, Texas, USA) used with the Intrepid cartridge (Alcon, Inc.), and the Signature (Abbott Medical Optics, Inc., Santa Ana, California, USA) unit, both tested in the peristaltic mode. Both machines were set at a measured bottle height of 75 cm using balanced salt solution (Alcon, Inc.), 550 mm Hg adjusted to the actual vacuum pressure at the tip, and a machine-indicated flow rate of 60 mL/minute.
In a masked fashion, with a towel around the handpiece handed to one of the testers, the tip was tapped lightly onto the capsule surrogate and removed immediately so that only the active vacuum at the tip was used. For each method tested, the tip was tapped against the plastic wrap in different places for a total of 200 taps (2 masked testers with 100 taps each). To show technique consistency, the results for the 2 testers were compared.
Two methods were tested. The first was aspiration only with a MicroSurgical Technology (MST, Redmond, Washington, USA)-prepared tip that was manufactured with the same tip dimensions except for the threads for each machine. Phacoemulsification tips tested had a 30-degree bevel, and types included 19- and 20-gauge typical sharp-edged tips, and 19- and 20-gauge needles with a radius tip edge (the Dewey Radius tip; MST). The second method tested was with the same tips and parameters, micropulsed longitudinal ultrasound with the Signature set at 6 milliseconds on and 12 milliseconds off at 10% and 100% power similarly. The third method tested also was with the same tips and parameters, Signature Ellips (Abbott Medical Optics, Inc.) at 100% power. The fourth method tested used Infiniti OZil (Alcon, Inc.) transversal ultrasound at 100% excursion and power with the same tips and parameters.
Capsular Breakage Experimentation on Fresh Human Cadaver Lenses
Twenty fresh human cadaver lenses were tested with the 2 machines at exactly the same parameters listed. In this experiment, the lens was tapped gently in different places in a masked fashion until capsular breakage occurred, at which time the lens is no longer useable for testing. Our results were recorded as the number of taps per capsular break. Because of the limited number of lenses, this experiment was limited to: (1) Signature micropulse, 100% power at 6 milliseconds on and 12 milliseconds off with a 20-gauge radius tip (4 lenses); (2) the same Signature with the same parameters (100% power) with a rounded tip using the Ellips power modulation (4 lenses); (3) Infiniti OZil at 100% power (4 lenses), also with the same rounded 20-gauge tip; and (4) Signature Ellips at 100% power with a 20-gauge sharp needle (8 lenses).
Determination of Actual Flow and Unoccluded Flow Vacuum
The actual flow from each machine, using the same bottle height and parameters, also with the same 2 tips, was determined for the Signature and Infiniti (Intrepid cartridge) machines. We also determined the average unoccluded flow vacuum for these machines (10 runs for each machine) by a method we described previously.
Statistical Analysis
A chi-square analysis of breakage rates was used for comparison. Student t testing was used for comparison of vacuum and flow data. Statistical significance was set at P < .0014 after a Bonferroni correction for multiple comparisons.
Results
Results Using the Plastic Wrap as a Capsular Surrogate
Using aspiration alone with both of the machines and all of the needles, no breakage of the plastic wrap occurred at any time. We did find that with micropulsed and Ellips ultrasound at 100% power, the 19-gauge sharp tip was significantly more likely than the 20-gauge sharp tip to cause a membrane break ( P < .0001). Interestingly, for Infiniti with the Intrepid cartridge using OZil ultrasound, the reverse occurred, with the 20-gauge tip more likely to break the membrane than the 19-gauge tip ( P < .0001). For all methods, the sharp tip was more likely to break the membrane than the rounded tip ( P ≤ .0002 for all comparisons).
At 100% power, the 19-gauge sharp micropulsed ultrasound tip (Signature machine) had a greater membrane breakage rate ( P < .0001) than did either Ellips or OZil, both of which were statistically similar. However, micropulsed ultrasound at 10% power was significantly less likely to break the membrane than at 100% power or with either Ellips or Ozil ultrasound at 100% ( P < .0001).
With the 20-gauge sharp tip, Ozil was more likely to break the membrane than micropulse (100% power), which was more likely to break the membrane than Ellips ( P < .0001). With the dull 19-gauge needle (100% power), micropulse and OZil were similar and both were significantly more likely to break the membrane than Ellips ( P < .0001). With a 20-gauge dull tip, Ozil was worse regarding membrane breakage than any of the other methods tested ( P < .0001; Table 1 ). In all cases, the differences between the 2 testers did not vary by more than 10%, so we were confident about the consistency of our technique.
| Tip Used | 100% Power (Signature 6 ms on/12 ms off) | 10% Power (Signature 6 ms on/12 ms off) | Ellips 100% Power | OZil 100% Power | P Values for Each Row |
|---|---|---|---|---|---|
| 19-gauge sharp | 184 (92%) | 9 (4.5%) | 130 (65%) | 123 (61.5%) | P < .0001 except Ellips and OZil similar |
| 20-gauge sharp | 117 (58.5%) | 13 (6.5%) | 78 (39%) | 168 (84%) | P < .0001 for all comparisons |
| 19-gauge dull | 8 (4%) | 0 | 0 | 11 (5.5%) | OZil more than Signature 10% and Ellips ( P = .0008) |
| 20-gauge dull | 2 (1%) | 0 | 0 | 45 (22.5%) | P < .0001 for OZil vs the other 3 |
| P values for each column | P < .0001 for all comparisons except 19- and 20-gauge dull, which are similar | P = .0002 for 20-gauge sharp vs both dull needles | P < .0001 for all comparisons except 19- and 20-gauge dull, which are the same | P < .0001 for all comparisons |
Human Lens Experimentation
Using the dull 20-gauge tip at 100% power, the capsular breakage rate for micropulse (2.3%) and Ellips (2.3%) was approximately half the capsular breakage rate observed with OZil (5.3%). This difference was not statistically significant; however, it most likely represents a study power issue. It was evident that looking at Ellips, the breakage rate of the 20-gauge sharp tip (25%) versus the 20-gauge dull tip (5.3%), the difference was both statistically significant and, most likely, clinically different ( P < .0001; Table 2 ).
| Signature (6 ms on/12 ms off) | Ellips 100% Power | OZil 100% Power | |
|---|---|---|---|
| 20-gauge sharp | Not tested | 4 ± 2 | Not tested |
| 20-gauge dull | 47 ± 12 | 47 ± 13 | 22 ± 11 |
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