Measurement - Perkins Mk2 Manuel D'instructions

en
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9.

Measurement

Measurement of the force necessary to flatten a corneal surface of constant (ø 3.06mm) size.
Dial indicator Force Pressure
1 9.81 mN 1.33 kPa = 10mm Hg
too light applanation
correct applanation
too heavy applanation
Fig 7
decentred
Adjust the force by turning the thumb-wheel (Fig 2, 8) until the inner margins of the
semicircles coincide (Fig 7).
The tonometer is removed from the eye and the reading noted. The large divisions of the
scale represent grams and the small divisions 0.2 gram.
The reading is multiplied by ten to give the tension in millimetres of mercury (mm Hg).
Readings should be repeated until a steady value is obtained; this will usually be slightly
lower than the initial reading.
If the semicircles appear large and are not reduced by diminishing the force of the spring,
the tonometer has been pushed too close to the eye and withdrawing it slightly will bring
the prism within the range of free movement.
If it is desired to use the Perkins tonometer without any forehead rest, the instrument can
be steadied by resting the fingers against the patient's malar region while the prism is in
contact with the cornea.
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