To Use The Instrument On Animals; Special Precautions - Perkins Mk2 Manuel D'instructions

en
8. General Notes
8. Astigmatism
1
For example
If the corneal astigmatism amounts to
6.5 mm/ 30˚ = 52.0 D/30˚ and
8.5 mm/120˚ = 40.0 D/120˚
the graduation value 120˚ of the prism is set at the 43˚ mark of the prism holder.
If there is a corneal astigmatism of
8.5mm/30˚ = 40.0D/30˚ and
6.5mm/120˚ = 52.0D/120˚
the graduation value 30˚ is set at the 43˚ mark.
In other words, set the axial position of the greatest radius, that is the axis of a minus
cylinder, on the prism graduation at the red mark on the prism holder.

To use the instrument on animals

8.
2
Unfortunately, most animal eyes have a cornea that behaves differently from the human
cornea and the Fick-Maklakov law does not apply for the standard diameter of applanation.
It is necessary to remove the patient's forehead rest and calibrate the tonometer for each
species used. This can be done quite simply by connecting the anterior chamber to a
reservoir and taking tonometer readings at different pressure levels. In most cases, it will be
found that the tonometric reading is lower than that obtained for the human eye. The eyes
of rhesus and cynomolgus monkeys behave very similarly to the human eye, but those of the
rabbit and cat give lower readings.
8.

Special Precautions

3
The Perkins hand-held tonometer is a delicate precision instrument, carefully inspected
and certified. Each instrument has been tested at 0 - 5 gram positions on the scale
(1 gram increments) and found to be correct within the limits specified on the certificate
accompanying each tonometer. It is desirable to clean the calibrating weights, as well as the
prism, in an antiseptic solution, before checking the instrument, to minimize the risks of
cross-infection (see cleaning instructions accompanying the prisms for decontamination
instructions).
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