Dr.Siddharth Gautam& Dr.Pavitra Patel Resident Ophthalmology JNMC,Wardha

2. DEFINITIONS
 Tonometry is the procedure performed to determine the intraocular
pressure (IOP).
 “Normal” intraocular pressure (IOP) may be defined as that
pressure which does not lead to glaucomatous damage of the optic
nerve head.
 Such a definition cannot be expressed in precise numerical terms as-
1) Individuals show different susceptibility to optic nerve damage at
given pressure levels.
2) It also depends on the underlying form of glaucoma.
 The best we can do is to describe the distribution of IOP in general
populations to establish levels of risk for glaucoma within different
pressure ranges

3. HISTORY
1826-William Bowman Digital tonometry(as routine
examination)
1863-Albrecht von Grafe Designed first instrument to attempt to
measure IOP
1865-Donders
1880-Preistly
Further instruments followed
Indentation type(no anaesthetic was
used until 1884)
1885-Malkalov 1st Applanation tonometer
1905-Hjalmar Schiotz Indentation tonometry
1948,1955-Friedenwald Coefficient of ocular rigidity
1954-Goldmann Prototype Applanation
tonometer(constant area)
1972-Grolmann NCT
Grant Electronic indentation tonometer
Halberg Hand held tonometer

4. IDEAL TONOMETER
 Should give accurate and reasonable IOP measurement
 Convenient to use
 Simple to calibrate
 Stable from day to day
 Easier to standardize
 Free of maintenance problems

5. FACTORS INFLUENCING IOP
 Rate of aqueous formation
 Resistance of aqueous outflow ( drainage)
 Increased episcleral venous pressure
 Dilatation of pupil
 Heredity
 Age
 Sex
 Diurnal variation
 Postural variation
 Blood pressure
 Osmotic pressure of blood

6. Tonometry Direct
ManometryIndirect
TYPES OF TONOMETRY

7. INDENTATION APPLANATION
Schiotz Variable force
Examples- GAT, Perkins, MMT,
Tonopen, Pneum. Tonometer
Mercurial Constant force
Examples- Maklakov, Glucotest,
Applanometer
Electronic
Scleral Tonometry

8.  Vogelsang 1927 – Ballistic Tonometer .The rebound of
a small metal ball from the eye is measured and this
depends to a large extent on the physical properties of
the coats of the eye.
 Roth & Blake 1963- Vibration tonometer cause
minimal deformation by oscillating force by a probe,
which also functions as a sensor and measures the
resonant frequency of the eye.

9.  Newer tonometers
1. Trans –palpebral
Tonometer
2. Disposable tonometer
Tonosafe – acrylic biprism
Tonoshield- silicone
shield
3. Dynamic contour
tonometer
4. Ocular Response Analyzer

10. A.HIGH DISPLACEMENT
TONOMETERS
B.LOW DISPLACEMENT
TONOMETERS
Tonometers that displace a large
volume of fluid and consequently
raise IOP significantly.
Tonometers in which the IOP is
negligibly raised during tonometry
(less than 5%).
Examples
1. Schiotz.
2. Maklakov.
Examples
1. Goldmann Applanation
Tonometer.
2. Mackay-Marg tonometer.
The Goldmann tonometer displaces
only 0.5 μl of aqueous humor and
raises IOP by only 3%.
Less accurate More accurate

11. MANOMETRY
Needle inserted into the AC through a self-sealing, beveled
corneal puncture
Movement of membrane, recorded optically or
electronically, is a measure of IOP.
Tubing can also be connected to a fluid-filled reservoir that
has a pressure-sensitive membrane.
Height of the fluid in the tubing corresponds to IOP.
Needle is connected to a fluid-filled tubing

12.  DISADVANTAGES:
1. Not practical method for
human beings.
2. Needs general anesthesia.
3. Introduction of needle
produces breakdown of blood
aqueous barrier and release of
prostaglandins which alter
IOP.
 USES:
1. It is used for continuous
measurements of IOP.
2. Used in experiment, research
work on animal eyes.

13. TONOMETRY
 It is an indirect method of measuring the IOP.
 It includes digital tonometry.
 Three basic types of Tonometers:
o Indentation
o Applanation(flattening)
o Non-Contact

14. DIGITAL
TONOMETRY/PALPATION
METHOD
 Intraocular pressure (IOP) is estimated by response of
eye to pressure applied by finger pulp.
 PROCEDURE: Patient looks down
Index finger of both hands used
One finger is kept stationary which feels the fluctuation
produced by the indentation of globe by the other finger.
If IOP is raisedfluctuation produced is feeble or absent and
the eyeball feels firm to hard.
When the IOP is very loweye feels soft like a partially filled
balloon.

15. `
ADVANTAGES DISADVANTAGES
Easiest to perform Reading not proper
No equipment Only depends on examiner
No anaesthesia Over-estimation or under-
estimation
No staining
Estimation of IOP with irregular
corneas,where applanation
tonometry not possible.

16. INDENTATION TONOMETRY
 All clinical tonometers measure the IOP by relating a
deformation of the globe to the force responsible for
the deformation.
 In indentation tonometry, a known weight is placed on
the cornea, and the IOP is estimated by measuring the
deformation or indentation of the globe.
 Eg-Schiotz tonometer

17. Parts of schiotz tonometer
scale
needle
Weight 5.5g
plunger
holder
Foot plate
lever
3mm diameter
ROC 15mm
Tonometer weight = 11g
Additional weights
7.5,10,15g

18.  The extent to which cornea is indented by plunger is
measured as the distance from the foot plate curve to
the plunger base and a lever system moves a needle on
calibrated scale.
 The indicated scale reading and the plunger weight are
converted to an IOP measurement.
 More the plunger indents the cornea, higher the
scale reading and lower the IOP
 Each scale unit represents 0.05 mm protrusion of
the plunger.

20. PRINCIPLE
 When the plunger indents the cornea, the baseline or
resting pressure(Po) is artificially raised to a new
value(Pt).
 Change in pressure from Po to Pt  Expression of
resistance an eye offers to displacement of a volume of
fluid (Vc).
 Because the tonometer actually measures Pt , it is
necessary to estimate Po for each scale reading &
weight.
Pt=P0 + E(Scleral Rigidity)

21.  Friedenwald’s gave a mathematical formula.
 The formula has a single numerical constant, the coefficient
of ocular rigidity (K), which is roughly an expression of the
distensibility of the eye.Its average value is 0.025.
 He developed a nomogram for estimating K on the basis of
two tonometric readings with different weights
in which Pt1 , and V1 , represent the tonometric pressure and
the volume of the indentation caused by the bar in the
determination made with the first weight, whereas Pt2 and V2
represent the respective values as obtained with the second
weight.
Log Pt2/Pt1 = K (V2-V1)

22.  On the basis of this formula, he developed a set of
conversion tables for IOP.
Plunger Load
Scale Reading 5.5 g 7.5 g 10 g 15 g
3.0 24.4 35.8 50.6 81.8
3.5 22.4 33.0 46.9 76.2
4.0 20.6 30.4 43.4 71.0
4.5 18.9 28.0 40.2 66.2
5.0 17.3 25.8 37.2 61.8
5.5 15.9 23.8 34.4 57.6
6.0 14.6 21.9 31.8 53.6
6.5 13.4 20.1 29.4 49.9
7.0 12.2 18.5 27.2 46.5
7.5 11.2 17.0 25.1 43.2
8.0 10.2 15.6 23.1 40.2
8.5 9.4 14.3 21.3 38.1
9.0 8.5 13.1 19.6 34.6
9.5 7.8 12.0 18.0 32.0
10.0 7.1 10.9 16.5 29.6

23. PROCEDURE
 Patient should be anasthetised with 4% lignocaine or 0.5% proparacaine
 With the patient in supine position, looking up at a fixation target while
examiner separates the lids and lowers the tonometer plate to rest on the
anesthetized cornea so that plunger is free to move vertically .
 Scale reading is measured.
 The 5.5 gm weight is initially used.
 If scale reading is 4 or less, additional weight is added to plunger.
 IOP measurement is repeated until 3 consecutive readings agree within
0.5 scale units.
 Conversion table is used to derive IOP in mm Hg from scale reading and
plunger weight.

24. OCULAR RIGIDITY
 Measure of distensibility or resistance to deformation of ocular
coats.
 Important in indentation tonometer
 Increase in ocular rigidity  increase IOP
 Long standing glaucoma
 ARMD
 High Hyperopia
 Vasoconstrictors
 Decrease in ocular rigidity  decrease in IOP
 Increasing age
 Strong Miotic therapy
 Vasodilator therapy
 Post operative after RD surgery(Vitrectomy,
cryopexy,scleral band)
 High Myopia
 Compressible gas

25. ADVANTAGES DISADVANTAGES LIMITATIONS
1. Portable 1. Falsely high/low IOP 
Ocular rigidity
1. Instrumental errors
2. Sturdy 2. Cannot be used in
traumatic cases/early
post op cases/corneal
diseases.
2. Muscular contractions
 of extraocular muscles
raises IOP
 Accomodation
decreases IOP
3. Relatively inexpensive 3. Variations in volume of
globe
 Micropthalmos
 High myopia
 Buphthalmos
4. Easy to operate 4. Recorded in supine
position only.
5. Easy to clean & maintain 5. Reading also influenced
by the size of the footplate
hole and the thickness and
curvature of the cornea.
6. Does not require slit
lamp/power supply.

26. CALIBRATION CHECK
PROCEDURE
 A calibration check should be done at the start of
every day. Place the footplate of the instrument on
the rounded test block (the dummy cornea)
provided with the tonometer’s storage case.
 With the footplate resting on the test block, a
correctly calibrated instrument will have a scale
reading of zero.
 If not, you can calibrate it to zero.
 If the needle is to the left of zero, rotate the
footplate in a clockwise direction and check again.
 If the needle is to the right of the zero position,
rotate the footplate in an anti-clockwise direction.

27. STERILIZATION
 The tonometer is disassembled between each use and the
barrel is cleaned with 2 pipe cleaners, the first soaked in
isopropyl alcohol 70 % or methylated spirit and the
second dry.
 The foot plate is cleaned with alcohol swab.
 All surfaces must be dried before reassembling.
 The instrument can be sterilized with ultraviolet radiation,
steam, ethylene oxide.
 In between patients, the Schiotz tonometer should be
disinfected by soaking it in sodium hypochlorite.
 As with other tonometer tips, the Schiotz can be damaged by
some disinfecting solutions such as hydrogen peroxide and
bleach.

28. DIFFERENTIAL TONOMETRY
 It is done to get rid from ocular rigidity.
 A reading is taken with one weight on the Plunger and then a
second reading' is taken with a different weight.
 Making a diagnosis of glaucoma in a pt. with myopia presents
unusual difficulties. The low ocular rigidity in these eyes result in
Schiotz readings within normal limits.
5.5g 10g Ocular rigidity IOP
18 mm Hg 15 mm Hg lower >18
18 mm Hg 21 mm Hg higher <18
18 mm Hg 18 mm Hg equal 18

29. ELECTRONIC SCHIOTZ
TONOMETER
 Has a continuous recording of IOP that is used for
tonography.
 ADVANTAGE:
Scale is magnified, which makes it easier to detect
small changes in IOP.

30. IMPACT-REBOUND
TONOMETER
 New and updated version of an indentation
tonometer.

31. PROCEDURE ADVANTAGES DISADVANTAGES
Sterile probe is propelled forward
into the cornea by a solenoid; the
time taken for the probe to
return to its resting position and
the characteristics of the rebound
motion are indicative of the IOP
(and also the biomechanical
properties of the cornea)
1. Very light
2. Disposable
3. Probe is extremely
light and its contact
with the cornea is
very short , used
without first
anesthetizing the
eye.
1. Tend to read
slightly higher
than the
Goldmann.
2. Accuracy falls off
in scarred
corneas.
Time taken for the probe to
return to its resting position is
longer in eyes with lower IOP and
faster in eyes with higher IOP.
4.Comparable to the
Goldmann in both
normal and post-
keratoplasty human
eyes.
Rebound tonometer does
correlate, like the Goldmann, with
central corneal thickness.
5.Used in screening
situations when
patients are unable to
be seated or measured
at the slit lamp.

32. APPLANATION TONOMETRY
(Haag Streit, Koeniz, Switzerland)

33. PARTS OF GOLDMANN
APPLANATION TONOMETER
Biprism
(measuring prism)
Feeder arm
Housing
Adjusting knob
Connects to the slit
lamp
Control weight insert

34. PRINCIPLE
 The concept was introduced by Goldmann is 1954.
 It is based on IMBERT FICKS LAW.
 It states that the pressure inside an ideal sphere (P) is equal
to force (F) necessary to flatten its surface divided by the
area of the flattening (A).
 P can be determined if
Force F is fixed or
Area A is fixed
P=F/A

35.  The ideal sphere is dry, thin-walled and flexible.
 The cornea is not ideal sphere.
 Two extra forces acting on cornea -
 Capillary attraction of tear meniscus (T), tends to pull
tonometer towards cornea
 Corneal rigidity (C) resists flattening
 Thus, Modified Imbert Ficks Law
F = PA , becomes
F + T = PA + C , or
P =( F + T - C) / A

36.  These two forces cancel each other when flattened area has
diameter of 3.06 mm.
 Applanation tonometry displaces only about 0.5 microlitre of
aqueous humor, which raises IOP by about 3%. Because the
volume displaced is so small, ocular rigidity, or the
‘stretchability’ of the globe, has little effect on the pressure
readings.

38. PROCEDURE
Patient is asked not to drink alcoholic beverages or large amounts of
fluid (e.g., 500 ml or more) for 2 hours before the test, as the former
will lower IOP and the latter may raise it.
Patient is told the purpose of the test and is reassured that the
measurement is not painful. The patient is instructed to relax,
maintain position, and hold the eyes open wide.
One drop of a topical anesthetic, such as 0.5% proparacaine, is
placed in each eye, and the tip of a moistened fluorescein strip is
touched to the tear layer on the inner surface of each lower lid.

39. Tonometer tip is cleaned with a sterilizing solution, and the tip and
prism are set in correct position on the slit lamp.
Tension knob is set at 1g. If the knob is set at 0, the prism head may vibrate
when it touches the eye and damage the corneal epithelium. The 1 g position
is used before each measurement. As a rule, it is more accurate to measure
IOP by increasing rather than decreasing the force of applanation.
0 graduation mark of the prism is set at the white line on the prism
holder.
Cobalt blue filter is used with the slit beam opened maximally. The
angle between the illumination and the microscope should be
approximately 60°.The room illumination is reduced.

40. Heights of the slit lamp, chair, and chin rest are adjusted until the
patient is comfortable and in the correct position for the measurement.
Palpebral fissure is a little wider if the patient looks up. However, the gaze
should be no more than 15° above the horizontal to prevent an elevation of IOP
that is especially marked in the presence of restrictive neuromuscular disease
such as dysthyroid ophthalmopathy.
Operator sits opposite the patient, the assembly is advanced towards the
patient with the tester observing from the side until the limbal zone has
a bluish hue.
If the tonometer tip touches the lids, the fluorescein rings will
thicken, which may cause an overestimation of IOP.

41. Clinician observes the applanation through the biprism at low power.
A monocular view is obtained of the central applanated zone and the
surrounding fluorescein-stained tear film.
Using the control stick, the observer raises, lowers, and centers the
assembly until two equal semicircles are seen in the center of the
field of view.
If the two semicircles are not equal in size, IOP is overestimated.The
clinician turns the tension knob in both directions to ensure that the
instrument is in good position.
If the semicircles cannot be made ‘too small,’ the instrument is too
far forward. If the semicircles cannot be made ‘too large,’ the
instrument is too far from the eye.

42. Fluorescein rings should be approximately 0.25–0.3mm in
thickness – or about one-tenth the diameter of the flattened area. If
the rings are too narrow, the patient should blink two or three times
to replenish the fluorescein.
If the fluorescein rings are too narrow, IOP is underestimated.
The tension knob is rotated until the inner borders of the fluorescein
rings touch each other at the midpoint of their pulsations.
Intraocular pressure is measured in the right eye until three
successive readings are within 1 mmHg. Intraocular pressure is then
measured in the left eye.
Reading obtained in grams is multiplied by 10 to give the IOP in
millimeters of mercury.

43. cont….
The fluorescent semicircles are viewed
through the biprism and the force against
the cornea is adjusted until the inner
edges overlap.
The fluorescein rings should be
approximately 0.25–0.3 mm in
thickness – or about one-tenth the
diameter of the flattened area.

44. POTENTIAL SOURCES OF
ERROR
FALSELY LOW IOP FALSELY HIGH IOP
Too little fluoroscein Too much fluoroscein
Thin cornea Thick cornea
Corneal edema Steep cornea
With the rule astigmatism
 1mm Hg per 4D
Against the rule astigmatism
 1 m Hg per 3D
Prolonged Cataract Wider meniscus
Repeated tonometry Widening the lid fissure
excessively
Elevating the eyes more than
150

45.  Wider meniscus or improper vertical alignment gives
higher IOP readings
 If the two semicircles are not equal in size, IOP is
overestimated.
 For every 3D increase in corneal curvature, IOP raises
about 1 mm Hg as more fluid is displaced under steeper
corneas causing increase in ocular rigidity
 More than 6 D astigmatism produces an elliptical area
on applanation that gives erroneous IOP. 4D with-the-
rule astigmatism underestimate IOP and 4D against-the-
rule astigmatism overestimate IOP.
 Mires may be distorted on applanating on irregular
corneas .

46.  Elevating the eyes more than 15° above the
horizontal causes an overestimation of IOP.
 Widening the lid fissure excessively causes an
overestimation of IOP
 Repeated tonometry reduces IOP, causing an
underestimation of the true level.This effect is greatest
between the first and second readings, but the trend
continues through a number of repetitions.
 A natural bias for even numbers may cause slight errors
in readings.

47. EFFECT OF CENTRAL
CORNEAL THICKNESS
 THINNER cornea  less force to applanate 
Underestimation
 THICKER cornea  more force to applanate 
Overestimation
 Goldmann applanation tonometer was designed to give
accurate readings when the CCT was 550 μm.
The deviation of CCT from 550 μm yields a change in
applanation readings of 0.7 mm Hg per 10 μm.

48.  IOP measurements are also modified after PRK and
LASIK.
 Thinning of the central cornea is gives lower readings
on applanation.

49. Potential Sources of Error – During Measurement

50. Potential Sources of Error – During Measurement

51. Potential Sources of Error – During Measurement

52. Potential Sources of Error – During Measurement

53. Potential Sources of Error – During Measurement

54. Potential Sources of Error – During Measurement

55. Potential Sources of Error – During Measurement

56. Potential Sources of Error – During Measurement

57. Potential Sources of Error – During Measurement

58. Potential Sources of Error – During Measurement

59. ADVANTAGES
Most accurate
No indentation, so not much
force is applied on cornea
Does not get affected by
corneo-scleral rigidity
Readings are directly from
knob
Can be done on post op
cases/injury cases
DISADVANTAGES
Need slit lamp
Dark room
Need staining & cobalt
light

60. CALIBRATION
 Goldmann tonometer should be calibrated at least once
a month.
 If the Goldmann tonometer is not within 0.1g
(+1mmHg) of the correct calibration, the instrument
should be repaired; however, calibration errors of up to
+2.5 mmHg may still be tolerated clinically.

61. STERILIZATION
 Biprism should be rinsed and dried immediately after
use.
 Between uses, the prism head should be soaked in a
solution such as diluted bleach or 3% hydrogen
peroxide.
 70% ethanol and 70% isopropanol are effective as
sterilizing solutions but were shown in one study to
cause mild damage to the tonometer tip after one month
of immersion.

62.  Other methods of sterilization include: 10 min of
rinsing in running tap water, wash with soap and water,
cover the tip with a disposable film, and exposure to
UV light.
 It is possible to transfer bacteria, viruses, and other
infectious agents with the tonometer head, including
such potentially serious infections as epidemic
keratoconjunctivitis, hepatitis B, Jacob-Kreutzfeld and,
theoretically, acquired immunodeficiency syndrome.

63.  Care must be taken to be sure any sterilizing solution
has been completely rinsed off the tonometer tip, as
some of these solutions may be toxic to the corneal
epithelium, especially after LASIK or other corneal
procedures.
 If the tonometer tip is not mechanically wiped after
each use, epithelial cells may stick to the tip with the
small but serious risk of transmitting Jacob-Kreutzfeld
virus.
 Disposable tonometer tips may be an acceptable
alternative to soaking in, and wiping with, antiseptic
solutions.

64. PERKIN’S TONOMETER
 Similar to the Goldmann tonometer.
 ADVANTAGES OVER
GOLDMANN TONOMETER:
 Portable and counterbalanced, so it
can be used in any position.
 Therefore,useful in a number of
situations, including in the operating
room, at the bedside, and with
patients who are obese or for other
reasons cannot be examined at the
slit lamp.

65. DRAEGER TONOMETER
 Similar to the Goldmann and
Perkins tonometers.
 Except :
Uses a different biprism.
Force for applanation is supplied
by an electric motor.

66. MacKay-Marg Tonometer
 1.5 mm diameter
plunger
 Rigid spring
 Rubber sleeve.
 Movement of plunger
is electronically
monitored by a
transducer and
recorded on a moving
paper strip.

67.  USEFUL FOR MEASURING IOP IN EYES
WITH:
1. Scarred, irregular, or edematous corneas
2. Accurate when used over therapeutic soft contact
lenses.

68. TONOPEN
 Same principle as that of Mackay-Marg tonometer.
 Battery operated, portable.
 USES:
1. Community health fairs
2. Ward rounds
3. Children
4. Irregular surfaces
5. Measuring through an amniotic membrane patch graft.
 A disposable latex cover which is discarded after each use
provides infection control.

69. TONOPEN
• For pressures from 6 to 24 mmHg, it measured an average of
1.7 mm higher than the Goldmann tonometer.
• Above 24 mmHg, the readings were similar.

70. DISADVANTAGES Overestimate the IOP in infants so its
usefulness in congenital glaucoma
screening and monitoring is somewhat
limited.
In band keratopathy where the surface
of the pathology is harder than normal
cornea, the Tono-Pen tends to
overestimate the IOP.

71. PNEUMATIC TONOMETER

72.  Principle is similar to the MacKay-Marg tonometer.
 Cornea is applanated by touching apex by silastic
diaphragm covering sensing nozzle.
 It is connected to central chamber containing
pressurized air.
 There is pneumatic to electronic transducer.
 It converts the air pressure to recording on paper strip
and IOP is read.

73. MAKLAKOV TONOMETER
 Differs from the other
applanation instruments
 A known force is applied to
the eye, and the area of
applanation is measured – a
technique known as constant-
force rather than constant-area
applanation.
 The instrument consists of a
wire holder into which a flat-
bottom weight, ranging from
5 to 15g, is inserted.

74.  Surface of the weight is painted with a dye, such as
mild silver protein (Argyrol) mixed with glycerin, and
then the weight is lowered onto the cornea.
 During the procedure the patient is supine, and the
cornea is anesthetized.
 Weight is lifted from the cornea, and the area of
applanation is taken to be the area of missing dye,
which is measured either directly or indirectly from an
imprint on test paper.

75.  Intraocular pressure is inferred from the weight (W)
and the diameter of the area of applanation (d) by using
the following formula:
 Intraocular pressure is measured in grams per square
centimeter and is converted to millimeters of mercury
by dividing by 1.36.
Pt= W /π(d/2)2
 Displaces a greater volume of aqueous humor than the other
applanation devices (but less than a schiøtz tonometer),
which means that the IOP readings are more influenced by
ocular rigidity.
DISADVANTAGE:

76. OCUTON TONOMETER
 Hand-held tonometer.
 Works on the applanation principle.
 Probe is so light that it is barely felt and, therefore,
needs no anesthetic in most patients.
 Device is comparable to Goldmann tonometry but
tends to read higher than the Goldmann tonometer
when the cornea is thicker, and its accuracy may be
compromised by diurnal changes in corneal thickness.

77. NON-CONTACT TONOMETER
 Introduced by Grolman.
 Original NCT has 3 subsystems:
 1. Alignment system: It aligns patient’s eye in 3 dimensions.
 2. Optoelectronic applanation monitoring system:
 It comprises transmitter, receiver and detector, and timer.
 a. Transmitter directs a collimated beam of light at corneal
apex.
 b. Receiver and detector accept only parallel coaxial rays of
light reflected from cornea.
 c. Timer measures from an internal reference to the point of
peak light intensity.

78. 3. Pneumatic system: It generates a puff of room air
directed against cornea.

79. PRINCIPLE
 A puff of room air creates a constant force that momentarily
flattens the cornea. The corneal apex is deformed by a jet of
air.
 The force of air jet which is generated by a solenoid
activated piston increases linearly over time.
 When the reflected light is at peak intensity, the cornea is
presumed to be flattened.
 The time elapsed is directly related to the force of jet
necessary to flatten the cornea and correspondingly to IOP.
 The time from an internal reference point to the moment of
flattening is measured and converted to IOP.

80.  A puff of air of known area is generated against cornea
(B).
 At the moment of corneal applanation,a light (T),
which is usually reflected from the normal cornea into
space, suddenly is reflected (R) into an optical sensor
(A).
 When the sensor is activated by the reflected light, the
air generator is switched off. The level of force at
which the generator stops is recorded, and a computer
calculates and displays the intraocular pressure.

81. ADVANTAGES LIMITATIONS
 Screening procedure  IOP is near normal,accuracy
decreases with increase in IOP &
in eyes with abnormal
cornea/poor fixation.
 Can be operated by non-medical
porsennel
 No anaesthesia required
 No direct contact between
instrument & eye

82.  New NCT, Pulsair is a portable hand held tonometer.

83. I-CARE TONOMETER
 Handheld,portable & rebound tonometer.
 Turn on the unit by pressing the measurement button. It
will beep and then display LOAD.
 Place the single use probe into the collar and push the
measurement button again.
 When the I-care tonometer is ready to use, it is brought
to the patient’s eye with the central grove in the
horizontal position.

84.  The distance of the eye to
the tip of the probe is from
4-8 millimeters.
 Press the measurement
button and take no less
than six measurements.
 After the six
measurements the IOP
will be displayed.

85. TRANS-PALPEBRAL
TONOMETER

86. PRINCIPLE USES LIMITATIONS
Pressure on the eyelid
in most eyes
produces retinal
phosphenes.
Young children Scleral rigidity
Pressure on the eyelid
required to induce
these phosphenes is
proportional to the
intraocular pressure.
Demented patients
and severely
developmentally-
challenged patients.
Thickness of the
eyelids
Portable patients can
measure their own
IOP at home
Orbicularis muscle
tone
Potential intra
palpebral scarring

87. DYNAMIC CONTOUR
TONOMETRY
Introduced by Kanngiesser

88.  Based on Pascal’s Law of Pressure, which states that
pressure applied to a confined fluid is transmitted
undiminished throughout the confining vessel of the
system.
 Concave shape of the tip generates minimal corneal
distortion and theoretically eliminates errors in
measuring IOP induced by ocular rigidity when the
cornea is applanated with a flat tipped tonometer.
 Operated in a fashion similar to a goldmann
applanation tonometer.

89. Pascal Dynamic Contour Tonometer (A) utilizes the
principle that when the contours of the cornea and
tonometer match, then the pressure measured at the
surface of the eye equals the pressure inside the eye (B).

90.  Microchip-enabled, solid-state sensor embedded within
the tip records 100 IOP measurements per second and
averages them over fluctuations in ocular pulse
amplitude.
 Digital display shows the final averaged IOP as well as
a Q-value that can be used objectively to judge the
quality of the final measurement.

91. OCULAR RESPONSE
ANALYZER
 Ocular response analyser (ORA) is a non-contact (air puff)
tonometer that does not require topical anaesthesia and provides
additional information on the biomechanical properties of the
cornea.
 Uses an air pulse to deform the cornea into a slight concavity.
 Measures not one but two pressures at which applanation
occurs:
1. When the air jet flattens the cornea as the cornea is bent
inward .
2. As the air jet lessens in force and the cornea recovers.

92.  The difference between
the pressures at which
the cornea flattens
inward and outward is
measured by the machine
and termed corneal
hysteresis (CH).
 The machine uses this
value to correct for the
effects of the cornea on
measurement.

93.  IOP correlate well with Goldmann tonometry but, on
average, measure a few millimeters higher.
 Congdon et al found that a ‘low’ hysteresis reading
with the ORA correlates with progression of
glaucoma, whereas thin central corneal thickness
correlates with glaucoma damage.

95. Tonometry for special
clinical circumstances
Irregular
cornea
• Pneumatic tonometer-Preferred
• Goldmann,NCT,Tonopen-limited accuracy
Soft contact
lenses
• Pneumo tonometry,Tonopen
Gas filled
eyes
• Pneumatic tonometry,Tonopen

96. Flat AC
• Goldmann,pneumotonometer,tonopen do
not correlate well with manometrically
determined pressures.
Keratoprostheses
• Tactile assessment

97. REFERENCES
 BECKER-SHAFFERS GLAUCOMA 8th EDITION
 SHIELDS GLAUCOMA 6th EDITION
 ANATOMY & PHYSIOLOGY OF EYE
A.K.KHURANA
 DIAGNOSTIC PROCEDURES IN
OPHTHALMOLOGY -BY HV NEMA, NITIN NEMA

98. THANK YOU

99.  PG ACTIVITY ON TUESDAY(09/02/16)
 CASE-PROPTOSIS
 PRESENTER-DR.SURABHI SHARMA
 MODERATOR-DR.MALA KAMBLE
 CONDUCTOR-DR.SACHIN DAIGAVANE