Taking A Pressure Measurement - Perkins Mk2 Manuel D'instructions

en
4.

Taking a Pressure Measurement

The cornea is applanated with a measuring prism of organic glass that is fitted in a
ring shaped holder at the end of the feeler arm. The contact surface of the
measuring prism has a diameter of 7.0mm. It is planar with rounded edges to
obviate any damage to the cornea.
The measuring prism is brought into contact with the eye. The measuring drum is
turned to increase pressure on the eye until a continuously regular surface of
3.06 mm ø = 7.354 mm
The relationship between the measuring drum position, force and
The intraocular pressure in mm Hg is found by multiplying the drum reading by ten.
SI-Units according to standard ISO 1000
According to ISO 1000 the derived unit of force is the
N (Newton) and its decimal sub-multiple the mN (milli Newton).
The conversion of mm Hg into the SI pressure unit kPa (Kilo
Pascal) can be made on the comparison scale in Fig 3.
The measurement of the flattened surface is made directly on
the cornea. The built-in duplication system in the measuring
prism divides the image and displaces the two semi circular
halves from each other by 3.06 mm.
Before measuring, it will be necessary to anaesthetise the
cornea locally, to place a strip of fluorescein paper in the
conjunctival sac and switch on the blue filter of the tonometer.
The inner border of the ring represents the line of demarcation
between the cornea flattened by applanation and the cornea
not flattened.
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2
has been applanated.
Position of the
measuring drum
1
pressure on the applanation surface
Force Pressure
1.33 kPa
9.81 mN
=10mm Hg
mmHg k Pa
0
0
1
10
2
20
3
4
30
5
40
6
50
7
8
60
9
70
10
80
HAAG-STREIT BERN
Fig 3
Comparative scale