A new tube chamber system for evaluation of anterior chamber pressure during phacoemulsification tested in porcine eyes

Abstract

Aim: To measure the optimal anterior chamber pressure (ACP) for safe phacoemulsification using a new tube chamber system with internal pressure measurement function in the porcine eye.

Methods: The 20-gauge and 21-gauge straight tips with yellow and orange sleeves, respectively, were covered by a test chamber combined with a pressure sensor for measuring ACP. This was measured for 20s from 10s after starting aspiration in the linear mode using vacuum levels of 200 and 150 mm Hg with a 20-gauge tip, and 300 and 250 mm Hg with a 21-gauge tip. Using a porcine eye, a pressure sensor fixed with a 0.9 mm corneal incision measured ACP. For the posterior capsule contact assay, porcine eyes were treated as described above, and the ultrasonic needle tip was held at the height of the iris and aspirated for 30s in linear mode at a vacuum of 200 and 150 mm Hg for the 20-gauge tip, and 300 and 250 mm Hg for the 21-gauge tip. The bottle height at which the posterior capsule accidentally contacted the ultrasonic tip was recorded, and the estimated ACP was calculated.

Results: The internal pressure of the new tube chamber system and ACP from the porcine eye closely matched proportional changes at vacuum levels of 200 and 150 mm Hg with 20-gauge tips. Similarly, proportional changes at vacuum levels of 300 and 250 mm Hg with the 21-gauge tip were nearly equal. The bottle height at which the posterior capsule contacted with the tip and estimated ACP were 57.5±12.6 cm (20.2±7.9 mm Hg) at 200 mm Hg with a 20-gauge tip, 35.0±10.0 cm (16.6±6.3 mm Hg) at 150 mm Hg with a 20-gauge tip, 47.5±12.6 cm (18.7±8.7 mm Hg) at 300 mm Hg with a 21-gauge tip, and 32.5±5.0 cm (15.7±3.5 mm Hg) at 250 mm Hg with a 21-gauge tip.

Conclusion: A comprehensive understanding of this chamber system's characteristics and usage can resolve anterior chamber instability caused by changing preoperative settings on the phaco machine.

Keywords: anterior chamber stability; cataract surgery; settings; test chamber.

Figure 1. Changes in internal pressure with various phaco machine settings in the tube chamber

A: The average internal pressure in the non-occluded aspirate state with various settings for 20s from 10s after initiating aspiration in the linear mode was measured using the tube chamber. The internal pressure was measured at 10-cm bottle height intervals during internal pressures of 5-25 mm Hg in the non-occluded aspirate, and at 1-cm intervals during internal pressures of approximately 0 mm Hg in the non-occluded aspirate. Each experiment was repeated four times. B: The distribution of internal pressure at a vacuum level of 200 mm Hg with a 20-gauge tip was linear and may be represented by an approximate straight line (y=0.6296x-15.952, R²=0.9273). C: The distribution of internal pressures at a vacuum level of 150 mm Hg with a 20-gauge tip was linear and may be represented by an approximate straight line (y=0.6254x-5.2642, R²=0.939). D: The distribution of internal pressures at a vacuum level of 300 mm Hg with a 21-gauge tip was linear and may be represented by an approximate straight line (y=0.6889x-14.026, R²=0.9716). E: The distribution of internal pressures at a vacuum level of 250 mm Hg with a 21-gauge tip was linear and may be represented by an approximate straight line (y=0.6926x-6.8314, R²=0.9423).

Figure 2. Changes in ACP with various phaco machine settings in porcine eyes

The average ACP in the non-occluded aspirate state with various phaco machine settings for 10s from 10s after initiating aspiration in the linear mode was measured using the porcine eyes. The ACP was measured at 10-cm bottle height intervals from 80 to 10 cm. Each experiment was duplicated with two porcine eyes. A: The distribution of ACPs at a vacuum level of 200 mm Hg with a 20-gauge tip was linear and may be represented by an approximate straight line (y=0.45x-10.626, R²=0.9684). B: The distribution of ACPs at a vacuum level of 150 mm Hg with a 20-gauge tip was linear and may be represented with an approximate straight line (y=0.4932x-3.8108, R²=0.9932). D: The distribution of ACPs at a vacuum level of 300 mm Hg with a 21-gauge tip was linear and may be represented by an approximate straight line (y=0.4639x-9.225, R²=0.9651). D: The distribution of ACPs at a vacuum level of 250 mm Hg with a 21-gauge tip was linear and may be represented by an approximate straight line (y=0.5257x-5.9071, R²=0.9849). ACP: Anterior chamber pressure.

Figure 3. Bottle height at which the posterior capsule came into contact with the tip

The ultrasonic needle tip was held at the iris level, and vacuum was applied with various phaco machine settings for 30s in the linear mode using porcine eyes. The bottle height was lowered in 5-cm steps, and the bottle height at which the posterior capsule accidentally came into contact with the ultrasonic tip was recorded. A: Posterior capsule folds were confirmed upon touching the posterior capsule with the ultrasonic tip. B: The contacting bottle heights at vacuum levels of 150 and 200 mm Hg for the 20-gauge tip are presented as mean±SD from 10 independent experiments. C: The contacting bottle heights at vacuum levels 250 and 300 mm Hg for the 21-gauge tip are presented as mean±SD from 10 independent experiments.