31
If more accuracy is desired, the intensity in the eye at the transducer focus
(corresponding to maximum intensity) may be calculated according to the formula
recommended by the FDA:
(
)
It
Iw
e
f
z
=
×
−
×
×
0 069
.
where
It
is the estimated in situ intensity,
Iw
is the measured intensity in water at the
focus of the transducer (indicated in the above chart),
f
is the ultrasonic frequency, and
z
is the distance from the face of the probe to the transducer focus, which is the point
of measurement (1 millimeter). The nominal frequency of these transducers is 20 MHz.
The actual frequency of a particular transducer may vary from this value. The tissue
calculations above were done with the measured frequency of the transducer used for
the tests.
XI.D. Biometric Measurement Capabilities
The DGH 550 can be ordered with one of three different measurement options.
Therefore, the biometric measurement capabilities of a particular unit will depend upon
which option is installed. The following table shows the measurement range for each
option.
Measurement Option
Range (
µ
m)
Accuracy (
µ
m) Display Resolution (
µ
m)
Standard Unit
200 - 1000
±
5
1
FLAP Option
95 - 1000
±
5
1
Extended Option
200 - 2000
±
5
1
XI.E. Classification
According to the degree of protection against electric shock, the
Pachette 2
is classified
as type B equipment. On CE units this is indicated by the symbol on the back
panel.