Methods of measuring intra
ocular pressure
What is intra ocular pressure ?
Definition
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Intra ocular pressure refers to the pressure
exerted by the intra ocular contents on the coats of
the eyeball.
 It is maintained by the equilibrium between the
aqueous humour formation, its outflow and the
episcleral venous pressure
Normal IOP – 10.2mmhg to 20.6mmhg
Types of Tonometer
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Schiotz Tonometer
Applanation Tonometer- Goldman
Tonopen
Pulse air Tonometer
Non contact Tonometer
Schiotz Tonometer
Devised in the year 1905
 Schiotz tonometer is the instrument which is used
to measure the intra ocular pressure ( IOP )
Requirements (Schiotz tonometer)
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Schiotz tonometer with 5.5gm ,7.5gm and 10gm
weight
Measurement chart (Friedan Wald chart)
4% Xylocaine as local anaesthetic
Wiper jar (Sterile)
Kidney type tray
Antibiotic drops (Chloramphenical )
2% propanolol &Tissue paper
Method
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Explain the procedure to the patient and make
him comfortable. He should be lying down with
head on the pillow.
Check the instrument by placing over the model.
Now the indicator ‘0’in the scale
Wash and dry hands.
Instill one drops of lignocaine 4%eyedrops in the
Eye (use pouch technique) – Explain the burning
sensation & other points
Allow 2to5minutes for the local drops to act.
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Ask the patient to look straight up
Separate the eyelids, putting no pressure on the eye.
Fingers should rest on the orbital margin.
Hold the tonometer so that footplate rests on the
center of the cornea.
Look at the scale of the Tonometer to find out the
degree of indentation. If the weight is not enough to
indent the cornea , use a heavier weight
Use the chart to calculate the intraocular pressure for
that particular weight, and that degree of indentation
Record the intraocular pressure in the patients note’s
Sterilizing the instruments
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Before replacing the tonometer, dismantle it and
clean the parts.
Remove the weights, unscrew the plunger and
clean them using swabs dipped in alcohol
Heat the footplate over the blue flame of the spirit
lamp for two minutes. Now the footplate is
sterilized
Keep the tonometer over the sterile wipers/pad so
that it cools down to room temperature
Check the instruments by placing over the model.
Now the indicator should show ‘0’in the scale
Tonopen
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Tonopen could be used
for children and adults
Before measuring, local
anesthetic drops are to be
applied
The patient can either sit
or lie down
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The tip of tonopen touches
the central part of cornea.
We should handle it
smoothly
This could be used for
patients who can not be
checked with Applanation
Tonometer &corneal
disorder patients & children
Pulse Air Tonometer
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Pulse Air Tonometer could
be used for all age group.
Mostly used for children
It could be used effectively
on children when they sleep
Only through air pressure
we will be able to measure
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This is an automatic
Tonometer
Need not use anesthetic drops
Normal value 12 to 21mmhg
Pulse Air Tonometer = Non
contact Tonometer
Distance of Tonometer &
Cornea is 10 to 12mm
Non contact Tonometer
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This is like the slit lamp
Patients is to be focused to see the red-light
inside the Tonometer
Picture of the eye could be seen on the screen
A white dot will be seen in the cornea
The MLOP should focus the white dot and click
it
At the time of focusing, if you see the word’Forward’ ,you should adjust the joystick in
front side.
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At the time of focusing, if you see the word-’Too
close’ ,you should adjust the joystick in back side.
Automatically the reading will be shown in the
screen itself
This will be useful for injury and redness and
post operative patients
No need to use local drops.
Applanation Tonometer
(Goldman’s)
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Goldman’s applanation Tonometer is capable of
measuring intraocular pressure accurately to 0.5mm
It is more accurate than Schiotz Tonometer
This is used with slit lamp microscope
It measures the area of the circle made flat by the
instrument on the flat and spherical part of the cornea
It has prism with external area of the Tonometer
A measuring drum attached to the slit lamp is inserted
into the handle over the chamber
Procedure
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Explain the method to the patient and keep the
patient in front of the slit lamp
Apply local anesthetic to the eye and add a drop
of flourescein with the help of a flourescein strip
Make the patients rest his chin in its place
Use blue filter to focus the conjunctiva, open the
slit beam, which is angled at 45-60° to the
chamber
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Make the patient open her eyes and keep that straight
.There should be no friction between the margin of the
lid and the instrument lest it causes the patient to
blink
When the patient is ready, arrange the measuring
drum. Move it along with slit lamp control lever so
that the Tonometer is near the centre of the cornea
Two bright yellow and green semicircles will be visible
through the eyepiece of the microscope. Focus them
with the help of the control lever so that the vertical
lines separating the two parts is equidistant from top
and bottom
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Adjust the measuring drum towards upper valves.
THE TWO SEMICIRCLES SUPERIMPOSE.
The reading at which the two semicircles
superimpose is noted.
Multiply the reading by 10. The intraocular
pressure is read in mm of Hg
Note
As the tonometer touches the cornea, it may cause
infection. So clean the applanating tip and sterilize
it with an antiseptic