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5.7 Operating the Instrument
1. Immediately before taking the measurements,
the patient should be made to close the eyes
briefly so that the cornea becomes sufficiently
moistened with the lacrimal fluid and
fluorescein.
2. By moving the tonometer forward, the
measuring prism is brought into contact with
the centre of the cornea over the area above
the pupils. The limbus of the cornea will be
illuminated with a bluish hue. This illumination
is best observed by direct sight from the
opposite side of the illumination unit by
the examiner.
As soon as the limbus of the cornea
illuminates, cease any further forward
movement of the tonometer immediately.
3. After obtaining contact, commence observing
the cornea. A regular pulsation of the two
semi circular fluorescein rings, which can be
of varying size dependent on the ocular
pressure, when the measuring drum is at
setting 1, will show that the tonometer is in
the correct measuring position
4. The pressure on the eye is increased by
turning the milled thumb wheel on the
tonometer, until the edges of both fluorescein
rings just meet (Fig. 7). The edges cross over
each other with the pulsation of the eye.
The width of the fluorescein ring around
the contact position of the measuring prism
should be 1/10 approx. of the diameter of the
applanation surface (0.3mm).
5. Reading the scale:
•
The reading
•
Multiplied by 10
•
Gives the ocular pressure in mm Hg
20
Note
The following are schematically
simplified illustrations.
Figure 6
Semi circular images in the centre
of the field of sight
Figure 7
Correct final position
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