Glossary of Fluidics and Phacodynamics Terminology
The following terms are commonly used in the discussion of fluidics and phacodynamics in phacoemulsification.
Aspiration flow rate (or flow rate)
The rate of removal of fluid and lens material from the eye through the tubing, measured in milliliters per minute (mL/min); produced by depressing the foot pedal to position 2 and continuing in position 3. Flow occurs when the aspiration port is not completely occluded, and the rate of flow helps determine how quickly fragments approach the aspiration port.
The opening at the end of an instrument (eg, phaco tip or irrigation/aspiration handpiece) through which fluid and lens material are removed from the eye.
A measure of how easily aspiration tubing is deformed by vacuum forces. Compared with low-compliance tubing, high-compliance tubing collapses more easily as vacuum builds, leading to a greater surge once occlusion has been broken and the tubing rebounds to an uncollapsed state.
A qualitative descriptor for how quickly and easily fragments are attracted to and held at the aspiration port. Distal followability (how quickly fragments are attracted to the aspiration port) is improved by increasing the aspiration flow rate. Proximal followability (how easily fragments are held at the aspiration port) is improved by increasing both aspiration flow rate (in the case of partial occlusion) and vacuum (in cases of partial and complete occlusion).
The pressure of the fluid coming through the irrigation tubing. It is controlled either by the irrigation bottle height (on a gravity-based machine) or by the intraocular pressure (IOP) setting (on a saline bag compression-based machine).
The influx of fluid into the eye, which is related to the infusion pressure.
An obstruction of the aspiration port or aspiration tubing that causes vacuum to build until it reaches the machine’s preset value or until the material is evacuated.
The time it takes for vacuum to build to a given level once the aspiration port has been occluded.
Surge (or postocclusion surge)
An undesirable phenomenon that occurs when vacuum has built up because of an occlusion and the occlusion is suddenly broken, causing the fluid in the higher-pressure (positive) anterior chamber to rush into the lower-pressure (negative) aspiration tubing. When the sudden egress of fluid exceeds the influx capability of the irrigation line, sudden shallowing of the anterior chamber may occur, and the iris or posterior capsule may be drawn into the aspiration port. Surge can be minimized by increased infusion pressure (ie, increased irrigation), lower vacuum, low-compliance tubing of smaller diameter, a smaller aspiration port, coiled aspiration tubing, and occlusion-mode software (including automatic modification of irrigation and aspiration flow rate).
The magnitude of negative pressure created in the aspiration tubing, measured in millimeters of mercury (mm Hg). Vacuum builds when the aspiration port is occluded, providing a gripping force; its strength determines how strongly particulate material will be held.
The maximum level of vacuum that a pump can produce upon complete occlusion of the aspiration port.