1. Tonometry is a clinical technique that measures intraocular pressure (IOP) by assessing the combined resistance of the eye's coats and IOP. A tonometer is a device that measures pressure on the optic nerves from fluid in the eyes. 2. Normal IOP ranges from 10-21 mmHg but an IOP over 21 mmHg increases glaucoma risk. IOP fluctuates throughout the day and is affected by various physiological and pharmacological factors. 3. Common tonometry methods include applanation, indentation, and air puff non-contact tonometry. Applanation tonometry like the Goldmann tonometer is currently the gold standard but techniques like Perkins, Tono-Pen, Sch

1. Tonometry
NISHITA AFRIN
B.OPTOM
3 RD B A T C H
ICO

2. Introduction
 Tonometery : It is a clinical technique that provides a
measurement of the eye , which includes the
combined resistance to deformity of its coats and the
intraocular pressure (IOP)
 Tonometer : A tonometer is a device that
measures the pressure placed on the optic nerves by
fluid in the eyes.

3. What is IOP ?
increased risk to develop glaucoma: >21mm
Hg

4. Factors modifying IOP
1.
Physiological variations : the IOP normally
fluctuates 2-5mmHg throughtout the day :
• with respiration and heart beat
• with time of the day
• with the venous pressure
• with the arterial pressure
• with the osmotic pressure of blood

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2. Local mechanical factors :
•
dilatation of the pupil
•
changes in the solid content of the eye
•
pressure from outside
3. Pharmacological factors:
The ciliary muscle is inserted into the trabeculum,
so the contraction of the ciliary muscle makes the
trabecular meshwork more porous -> increases
the facility of outflow -> reduces IOP
•
outflow facility
•
reduction of aqueous production
•
atropine

6. Measurement of IOP
 Manometry : it is measured by inserting a cannula,
directly into the anterior chamber which is
connected with a manometer.

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 Digital tonometry

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Instrumental tonometry
contact
tonometer


non contact
tonometer
indentation tonometer
Schiotz, Macky-Marg
Applanation tonometer
Goldmann,Parkin’s,Tono-pen

9. Clinical use
 diagnosis and management
 abnormally high IOP
 abnormal asymatric IOP
 abnormal diurnal IOP variations
 abnormal increase in the intraocular pressure over a
long period
 Suggest the presence of glaucoma

10. Commercially available instrument
 Goldmann tonometer
 parkines hand held tonometer
 McKay-Marg tonometer
 Schiotz tonometer
 Air puff
 tono-pen

11. Instruments
applanation tonometer

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Perkin’s
schiotz
tono-pen

13. Continue
Air puff

14. Applanation tonometry
Goldmann applanation tonometery
 The force necessary to flatten a given area of cornea
is measured
 concept introduced by Goldmann in 1954
 consists of double prism mounted on a standard slit
lamp
 standard area of cornea of 3.06 mm diameter has
been flattened

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 it based on Imbert-Fick law
it sates that the pressure in a sphere filled
with fluid and surrounded by an infinitely
thin,flexible membrane,may be measured by the
force that just flatten the membrane to a plane
surface
P
= W/ A

16. Procedure
 patients counseling
 dry, clean tonometer probe shoud be inserted
 slit lamp should be adjusted and the patient
comfortably positioned
 topical anesthetic
 place a fluorescein strip in the lower fornix
 room light should be dimmed
 illumination system should be at approximately 60
degree to the lateral side of the eye to be measured

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 keep both eyes open
 cornea and biprism is illuminated by cobalt blue
light from slit lamp
 biprism is then advanced until it just touches the
apex of cornea
 at this point 2 semi circles are viewed

18. Errors in Measurement
 The fluorescein ring is too wide or too narrow
 thin corneas produces underestimate
 thick cornea d/t increased collagen gives overestimate, if






d/t edema gives underestimate.
inadequate vertical alignment of semicircles leads to
overstimate of IOP.
distortion d/t irregular cornea influences accuracy, less
useful with corneal scarring.
squeezing of eyelids
repeated tonometry may induce decline in estimated IOP.
increase of 1 mmHg for every 3D increase in corneal power
tear film of cornea, anesthetic drops.

19. contraoindication
 Head trauma
 suspicion of ruptured globe
 narrow angle

21. Correction for astigmatism
 With semicircles displaced horizontally, IOP
underestimated by 1 mmHg for every 4D of
WTR astigmatism, vice versa for ATR astigmatism.

22. Tono-pen
 including its power source
• weight only 57g
• 185 mm long
• 25mm wide
 fully portable
 held in any position
 operated by index finger
 reading displayed as adigital readout located on the
handle
 are not affected by corneal astigmatism

23. perkin’s hand held
 same type of goldmann applanation probe
 applies force by counterbalanced arm
 applanated corneal surface viewed by a magnifying
lens situated behind the lens
 illumination buit into the instrument

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 used with patient in any position
 portable

25. INDENTATION TONOMETRY
Schiotz tonometer

free floating barrel with a footplateof 10.1 mm
 slightly flattents the cornea
 Total weight varies from 5.5g

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 Principal :
based on the principal, that a plunger
will indent a soft eye more than a hard eye.
 indication : all types of glaucoma,uveitis,hyphaema
 contraindication : corneal ulcer,
conjunctivities,panophthalmitis are in infectious
condition and
corneal abrasion,severe dry eye in noninfectious condition

27. procedure
 sterilization by boiling or wiping with alcohol
 Patients counseling
 use short acting topical anesthetic
 supine or in semi supine position
 fixation target
 separate the eyelid
 place tonometer directly onto the cornea vertically
 note scale reading
 antibiotic

28. Advantage and disadvantage
 Advantage :
cheap , portable, easy use
 Disadvantage : false reading with abnormal scleral
rigidity, corneal abrasion

29. What is ocular rigidity?
 The resistance of the coats of the eye to indentation

factors affecting rigidity :
1. Refective error : high in hyperopes
and lower in myopes
2. drugs : miotics reduce ,
vasoconstrictor rise
3. surgery : lowers

30. Non-contact tonometer
Air-puff tonometer


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 non-contact
 only screening purpose
 It applanates the cornea by means of a jet of air.
 Once the instrument is properly aligned with the
patient's eye, a fixed distance separates the cornea
from the instrument.
 An optical system measures the time that it takes for
the air puff to flatten the cornea.
 This can be correlated with the IOP.

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 Mean IOP readings compare favorably with
Goldmann tonometry
Advantage :The instrument is beneficial in mass
glaucoma screenings because it does not require
topical anesthetic and, with proper use, there is no
risk of injuring the cornea.

33. THANK YOU