tonometer and its purpose

1. PRESENTATION ON OPTONOMETRIC
INSTRUMENT
PRESENTED BY : LYNTIHUN SUKHLAIN
AND
ARENNUNGLA SANGLIR
TOPIC ON : TONOMETER

2. CONTENT :
INTRODUCTION
HISTORY
CLASSIFICATION OF TONOMETER
DIRECT TONOMETER
INDIRECT TONOMETER

3. HISTORY :
• The first tonometers were simple applanation types credited to
Adolf Weber in 1867 and the Maklakow in 1885 . Various designs of
impression-type of tonometers were produced in the latter part of
the last century .
• In 1905 an indentation tonometer was designed by Hjalmar August
Schiotz and this instrument , with various modifications become
the most widely used clinical method of estimating the IOP until
the introduction of applanation tonometer of Goldman in 1954.
Adolf Weber Hjalmar Schiotz Hans Goldmann

4. Introduction
TONOMETER : It is a device used to measured the intraocular
pressure of the eye . It is also used to help detect glaucoma.
• A tonometer measure the production of aqueous humor which the
liquid inside the eye , and the rate at which it drains into the
tissue surrounding the tissue
TONOMETRY : It is the procedure performed to determined the
intraocular pressure (IOP)
• Normal IOP range is 10-21 mm of Hg with an average of 16 ± 5.0
mm of Hg

5. CLASSIFICATION :
TONOMETER
DIRECT
MANOMETER
INDIRECT
DIGITAL INDENTATION APPLANATION NCT

6. DIRECT TONOMETER :
Manometer :
• Manometer is the only direct measured of IOP.
• In this method ,the needle is introduced in anterior
chamber or in the vitreous
• It is then connected to mercury or water manometer
Uses
• It is used for continuous measurements of IOP .
• It is used in experiment ,research work on animal eyes .

7. Disadvantages of manometer :
• Its is not practical method for
human eye .
• It needs general anesthesia
• Introduction of needle produce
breakdown of blood aqueous barrier
and released of prostaglandins
which alter IOP.

8. INDIRECT TONOMETER :
1.Digital tonometer : it is based on palpation by the examiner
 Procedure :
• the patient were ask to looks down.
• Index fingers of both hand is used one finger push the eyeball above the tarsal
plate and at that time other finger palpation the process .
 Advantages :
• It is easiest
• It does not need any equipment
• No anaesthesia and staining is required
 Disadvantages :
• The reading is not proper and it depend on the examiner only
• Minor IOP cannot judged properly .

9. 2. INDENTATION : Indentation tonometer is based on the fundamental
fact that a plunger will indent a soft eye more than a hard eye .
• The indentation in current use is of Schiotz ,invented by Hjalmar
Schiotz who devised in 1905 and continued to refined it through 1927.
• Because of its simplicity , reliability ,low price and relatively accuracy ,
it is the most widely used tonometer in the world .
Hjalmar Schiotz

10. Schiotz tonometer :
Schiotz tonometer is an indentation tonometer used to measure the IOP by measuring the
depth produced on the surface of the cornea by a load of known weight .
PARTS OF SCHIOTZ TONOMETER CONSISTS OF
1).Curved footplate which is placed on the cornea of a supine patient
2).Holder for holding the instrument in vertical position on the cornea .
3).Plunger which moves freely within a shaft in the footplate.
4).Lever arm whose short arm rests on the upper end of the plunger
5).Needle a long arm which act as a pointer
6).Scale its indicate the degree to which the plunger indents the cornea indicated by the
movement of the needle .
7).Weight a 5.5 gm weight is permanently fixed to the plunger , which can be increased
to 7.5 and to 10 gm .
8). Barrel it is hollow in shape at the centre of the holder and plunger

11. procedure of Schiotz tonometer :
• Before tonometry , the footplate and the lower end of plunger should be sterilized
.
• For repeated used in multiple patients it can sterilized by dipping the footplate in
either absolute alcohol, acetone or by heating the footplate in the flame of spirit
• The eye is anaesthesia the cornea with paracaine or 2-4 % of topical xylocaine and
patient is made to lie supine on a cough and instructed to fix a target on the
ceiling.
• Then examiner separate the lids with left hand and gently rests the footplate of
the tonometer vertically on the centre of cornea.
• Place the tonometer directly onto the cornea without sliding so that the footplate
rests centrally and the instrument is truly vertical.
• Then the reading on scale is recorded as soon as the needle become steady.
• It is customary to start with 5.5 gm weight however if the scale reading is less than
3,additional weight should be added to the plunger to make it 7.5 gm or 10 gm as
indicated ,since the Schiotz tonometer the greatest accuracy is attained if the
deflection of lever is between 3 and 4 .
• And lastly the tonometer is lifted and a drop of antibiotics is instilled.

12. • A calibration at the start of every day should be done ,
• Place the footplate of the instrument on the rounded test block.
• A correctly calibrated instrument the scale reading should be zero, if not
calibrate it into zero by:
i. Left of zero: rotate the footplate in a clockwise direction
ii. Right of zero:Rotate the footplate in an anti-clockwise direction
Advantages :
• It is handy and easy to used
• No need for slit lamp or power
supply
• It is cheap
• It is widely used tonometer
• Disadvantages:
• It gives false reading when
used in eyes with abnormal
scleral rigidity.
• False low levels of IOP are
obtained in eyes with low
scleral rigidity as seen in high
myopes .

13. 3.Applanation Tonometer :
The concept of applanation tonometer was introduced
by Hans Goldman in 1954 .
PRINCIPLE :It is based on Imbert-Fick Law which states
that the pressure inside a sphere (p) is equal to the
force(F) required to flattened it surfaced divided by
the area of flattening(A).
i.e, P = F/A
APPLANATION
TONOMTER
CONTACT
PNEUMATIC
TONOMETER
TONOPEN
TONOMETER
REBOUND
TONOMETER
NON-CONTACT
AIR PUFF
TONOMETER

14. APPLANATION TONOMETER
The most commonly used tonometers are :
1. Goldman tonometer : currently , it is the most accurate and
popular tonometer usually mounted on the standard slit lamp
biomicroscope. It is easy to use and measure the IOP of a seated
patient with high accuracy in most clinical situation .
• Applanation tonometer measurement are affected by the central corneal
thickness (CCT) . Thicker CCT may give an artificially high IOP measurement
, whereas thinner CCT can give an artificially low reading .

15. Parts of the Goldman applanation tonometer :
1. Biprism
2. Feeder arm
3. Housing
4. Adjusting knob

16. Procedure
• The dry clean tonometer probes should be inserted into the holder with it
zero axis marking aligned with the reference mark on the holder .
• The patient is positioned at the slit-lamp with the forehead firmly
against the headrest
• Topical anaesthetic and fluorescein are instilled into the
conjunctival sac
• With the cobalt blue filter ,and the brightest beam projected
obliquely at the prism. the prism is centered in front or the apex of
the cornea
• The dial is present between 1 and 2 (i.e.. between 10 and 20
mmHg)
• The prism is advanced until it just touches the apex of the cornea
• Viewing is switched to the ocular of the slit-lamp.
• A pattern of two semicircles will be seen , one above and one below
the horizontal midline which represent the fluorescein-stained tear
film touching the upper and lower outer halves of the prism .
• The dial on the tonometer is rotated to align the inner margins of

17. Calibration :
• GAT Should be calibrated periodically at least once a month .
• If it is not within 0.1 g (1 mmHg ) of the correct calibration , the instrument should be
repaired .
• The calibration bar is attached to the body of the tonometer , the bar have 5 markings :
i. the central one is used to check if the tonometer is calibrated accurate for 0 mmHg
ii. The next marking on either side of the centre are used to check for accurate
calibration for 20 mmHg
iii. The the last markings nearest to the end are used to check for 60 mmHg
iv. To check if tonometer has calibrated for 60 mmHg , line up the 6 marking on the knob
that hold up the bar .
v. now move the knob on tonometer and note the pressure at which tonometer tip tilt
forward .
vi. If the tilt occurs when the pressure is at 60 mmHg the tonometer is calibrated
correctly .
vii. If the tilt occurs below or above 60 mmHg , the tonometer should be sent for
recalibration

18. Advantages and Disadvantages of Goldman tonometer :
Advantages
• Its near universal acceptance as
the standard method of IOP
assessment .
• Ease of use from the
technician’s perspective
• Acceptability for most patients.
Disadvantages
• Its need for anesthesia
• Upright positioning and lack of
portability.
• As the device must come in
contact with the eye which
carries a small but real risk of
eye injury or infection if the tip
is not adequately sterilized
between patients.

19. 2. Perkins applanation tonometer :
It is a hand-held tonometer utilizing the same biprism as in Goldman
applanation tonometer also requiring topical instillation of fluorescein.
It was developed by ES Perkins in 1965
Part of Perkin’s tonometer :

20. Procedure :
• After preparation of the patient with a corneal anesthesia fluorescein
the Perkins tonometer is gripped in one hand with the thumb resting
on the knurled wheel.
• The wheel is turned to approximately 10 units on the scale this causes
the lamp to illuminate an area immediately behind the engraved line
on the prism
• The applanation probes may now be brought into contact with the
patients cornea
• With the prism centered on in contact with the cornea the knurled
wheel is adjusted until the fluorescein rings are apposition . Some
pulsation of the rings occurred synchronous with the cardiac pulse
wave .
• After used the tonometer should be removed carefully from its holder
and washed it in clean water ,wiped it with a disposable tissue .

21. Advantages
• It is small and easy to carry
• Does not required slit-lamp.
Disadvantages
• High level of skill to operate
• Decrease in stability with a
hand-held instrument
• Need for topical anesthesia
• Decrease accuracy on an
irregular or scarred cornea.

22. 1. Pneumatic tonometer :In this , the cornea is applanated by touching
its apex by a silastic diaphragm covering the sensing nozzle which is
connected to a central chamber containing pressurized air. In this
tonometer, there is a pneumatic-to-electronic transducer, which
converts the air pressure to a recording on a paperstrip, from where
the IOP is read .
It was first developed by Durham et al and refined by Langham and
McCarthy in 1969.
PRINCIPLE : The principle of the pneumatic tonometer involves a flowing
column of air directed towards a thin membrane that is in contact with the
surface of the cornea
CONTACT TONOMETER
1

23. 2. Tono-pen : It is a hand-held tonometer in the same manner
as a pen or pencil and the activation switch located on the
probe end of the body. The tono-pen must be calibrated.
Invented in 1987.
CALIBRATED METHOD : Calibration need only be performed at
the beginning of each day .
i. Hold down the switch until a beep sounds. The instrument will
show “====“. Release the switch and the display will be “----”
followed by another beep.
ii. Hold the instrument vertically with the probe down and press
the switch twice in rapid succession .
Turn the tonometer so that the probe is up and the instrument
vertical . A beep sound and the read out should be good.

24. Procedure
• Explain the procedure to the patient and apply a corneal
anesthetic
• position the patient with a fixation target located so that the
eyes are in the primary position and instruct the patient to look
at the target.
• Hold the tono-pen as you would a pen and place the index finger
over the switch .
• Lightly and briefly touch the cornea several times , each
successful reading is signaled by a click sound and when
sufficient readings have been made there will be a beep .

25. 3.Rebound tonometer (RT) : it is a hand-held ballistic
devices that measure the return bounce motion of an
object impacting the cornea.
It was invented by Antti Kontiola in 1997 and is still
available as Icare
PRINCIPLE : the hand-held battery-powered device
bounces a small lightweight disposable probe off the
cornea , measuring the deceleration and rebound time
to calculate the IOP .
R

27. Advantages
• it is easy to use
• No anesthetic required
Disadvantages
• It can only used in upright
position (the probe falls out if
the instrument is facing
downward )
PROCEDURE
• Make the patient sit in upright position so that the
probe will not fall down
• Ask the patient to look straight so that the probe
bounce at the center of the cornea .

28. 4.NON-CONTACT TONOMETER (NCT):
.Air-puff tonometer : It is a hand-held instrument that uses
the air-puff principle to cause distortion of the cornea .
It was invented by Keeler in 1986
Working of air-puff tonometer: a puff of air creates a
constant force that momentarily flattens the cornea and
internal reference point to the movement of flattening is
measured and converted into IOP directly reading on the
display part .

29. PROCEDURE :
• Make the patient sit in upright position .
• Place the air jet nozzle approximately 15mm from the patient cheek
and demonstrate to the patient the sound of the air jet intensity.
• Instruct the patient to look at the red target light in the nozzle and
to keep the eye wide open .
• Maintain the instrument alignment and look through the eyepiece .
• The tonometer will activate automatically when the correct
alignment is achieved
• Advantages
• It can be operated by non-
medical personnel
• No anesthesia required
• No contamination to the eye
• No chance of corneal abration
• Disadvantages
• IOP is near normal
• accuracy decrease in IOP and
in eyes with poor fixation

30. Reference
• A .k. Khurana ,comprehensive ophthalmology 7th edition ,chapter 23- clinical
methods in ophthalmology ,page no: 530-533.
• Jack k Kanski ,clinical ophthalmology – a systemic approach, chapter 1-
tonometry , page: 8-10.
• Clinical procedure