DORC 1100 Руководство по эксплуатации - Страница 6

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2.3

Theory of operation

Diathermy is used in operations for retinal detachment to produce a burn of the pigment epithelium.
This burn is obtained by the applications of localized RF current on the sclera.
A. Why High Frequency 13.56 MHz Power ?
The following consideration resulted in the selection of the 13.56 MHz :
1.
Clinical tests have established that this frequency produces optimum burns of the pigment
epithelium with the least possible damage to adjacent tissue such as the sclera and choroid.
2.
High frequency produces very small localized burns whereas low frequency produces larger
burns which are not as well localized.
3.
With high frequency, the impedance of the sclera crust formation has less variation than with
low frequency.
It is thus possible to obtain more consistent burns repeatedly. The nominal scleral impedance
is 600 ohms.
The Micro Diathermy has been designed for a maximum output level variation of less than ±
10% at each RF LEVEL setting for scleral impedance which may vary over a range of 400 to
1000 ohms. This inherent design feature allows for an even greater consistency of burn.
4.
Due to low impedance at high frequency, less voltage is required to produce a given burn than
at low frequency.
B. How a burn is produced :
The precise physiological and electrical characteristics of RF scleral application are not yet fully
known. Nevertheless, it is possible to distinguish three factors involved in producing a scleral RF
burn.
1.
The heat is produced by Joule's effect (the resistive part of the tissues in the current's path).
2.
In high frequency applications, the heat is produced by dielectric losses in the capacitive part
of the tissues.
3.
Propagation of heat generated by the crust formation under the electrode's tip.
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D.O.R.C. MICRO DIATHERMY SYSTEM
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