Haag-Streit Perkins MK3 Manual De Instrucciones página 19

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Adjust the force by turning the thumb-wheel (Fig 2,8) until the inner-margins of the
semicircles coincide (Fig 5).
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 grams.
Adjust the readings taking into account the age and biomechanics of the patient's eye.
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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