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Evolution of Ultrasound Pumps and

3

Fluidics and Ultrasound Power: From

Standard Coaxial Towards the Minimal

Incision Possible in Cataract Surgery

William J. Fishkind

Core Messages

ßIncreased capability of the phaco machine permits a considerable individualization of the phaco parameters.

ßThrough consideration of machine settings, the quality of cataract surgery and its outcomes can be appreciably improved.

3.1 Introduction

Although phacoemulsification machines have undergone continuous improvement, ever-increasing in both, their complexity and safety, one principle remains unchanged: All phaco machines consist of a computer to generate ultrasonic energy, and a transducer to turn these electronic signals into mechanical, acoustical, and cavitational energy. The energy thus produced, is transferred through a hollow needle and will overcome the inertia of the lens to emulsify it. The second of the refined elements of the machine are the “fluidic control systems.” These consist of a vacuum generating pump and computer algorithms to control it, phaco needles of varying diameters and configurations, and infusion sources.

Frequency is defined as the speed of the needle movement. The manufacturer of the machine determines it. Presently, most machines operate at a frequency between 27,000 cycles per second (Hz) to 50,000 cycles per second. This frequency range is efficient for nuclear emulsification. Lower frequencies become less efficient and higher frequencies create excess heat.

Stroke length is defined as the length of the needle movement. This length is generally 2–6 mils (thousandths of an inch). Most machines operate in the 2–4 mil range. One mil is 25 mm. Therefore, most phaco needles travel a distance of 50–100 mm. Longer stroke lengths and higher frequencies are prone to generate extra heat. The longer the stroke length, the greater is the physical impact on the nucleus, and so, the generation of cavitation energy is greater. When the frequency is higher, the impacts per unit time is more and the physical impact is greater.

3.2 Power Generation

Power is created by an interaction between frequency and stroke length.

W. J. Fishkind

Director Fishkind, Bakewell, Maltzman

Eye Care and Surgery Center

Tucson, Arizona, USA

3.3.1 Tuning

The central processing unit (CPU) of modern phaco machines recognizes the phaco needle when it passes into different intraocular media. It does this by turning the driver piezo crystals, momentarily, into receiving crystals. The system is most efficient when it is operating

J. L. Alió, I. H. Fine (eds.), Minimizing Incisions and Maximizing Outcomes in Cataract Surgery,

37

DOI: 10.1007/978-3-642-02862-5_3, © Springer-Verlag Berlin Heidelberg 2010