Tonometry ppt_slide_Notes_download .pdf

Definition:
Tonometry is the procedure used to measure intraocular pressure (IOP) — the fluid pressure inside the eye. It helps in the diagnosis and management of glaucoma, ocular hypertension, and other eye diseases affecting the optic nerve and cornea.


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Purpose / Importance:

Maintaining normal intraocular pressure (10–21 mmHg) is essential for the shape and function of the eyeball. If the pressure increases (as in glaucoma), it can damage the optic nerve leading to vision loss. Tonometry helps to:

Detect abnormal IOP early.

Monitor IOP changes after treatment or surgery.

Evaluate the risk of developing glaucoma.



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Principle:

The basic principle of tonometry is derived from the Imbert-Fick law, which states:
The pressure inside a thin-walled sphere equals the force required to flatten its surface divided by the area flattened.
In simple terms, by applanating (flattening) or indenting a known area of the cornea with a specific force, the intraocular pressure can be calculated.


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Types of Tonometry:

1. Indentation Tonometry:

Measures IOP by indentation (pressing) the cornea.

Example: Schiotz Tonometer.

Principle: Higher IOP resists indentation; lower IOP allows deeper indentation.

Requires patient to be in a supine position and uses weights to indent the cornea.



2. Applanation Tonometry:

Measures the force needed to flatten a specific area of the cornea.

Example: Goldmann Applanation Tonometer (GAT) – the gold standard.

Based on Imbert-Fick law, gives highly accurate results.

Usually performed at slit lamp using fluorescein dye and cobalt blue light.



3. Non-contact Tonometry (Air-puff):

Uses a puff of air to flatten the cornea without touching it.

No anesthesia or direct contact needed.

Useful for screening and in infection control.



4. Dynamic Contour Tonometry (DCT):

Uses a pressure sensor that matches the corneal contour to give continuous and accurate IOP reading.

Minimizes corneal influence.



5. Rebound Tonometry (Icare):

A small probe bounces against the cornea; the deceleration speed is used to calculate IOP.

Portable, no anesthesia, and ideal for children or uncooperative patients.





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Procedure (Goldmann Applanation Example):

1. Instill fluorescein dye and topical anesthetic in the eye.


2. Adjust the slit lamp and blue light.


3. Align the tonometer prism with the cornea.


4. Observe the fluorescein semicircles and adjust the knob until their inner borders just touch.


5. Multiply the scale reading by 10 to get IOP in mmHg.




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Factors Affecting Tonometry:

Corneal thickness (CCT): Thicker cornea = falsely high IOP; thinner cornea = falsely low IOP.

Corneal curvature and elasticity.

Patient’s position, blinking, and pressure on the globe.



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Precautions:

Avoid pressing on the eyelids.

Disinfect the tonometer tip after each use.

Ensure correct calibration of the instrument.

Do not perform on eyes with corneal ulcers .
#iop #tonometer #tonometry #applanation #ind.

1. Tonometry:-
Measurement of intra Ocular pressure.
Presented by:- ANMOL SINGH
BOPTOM 2K24
UPUMS SAIFAI ETAWAH

2. Introduction:-
●Tonometry = Measurement of intraocular
pressure (IOP).

●Essential test in glaucoma diagnosis &
management.
. IOP balance between aqueous humor
production & drainage.

3. Tonometry:
● Technique used to determine the
intraocular pressure by
measuring the eye’s resistance
to indentation or flattening.

4. Normal Intraocular Pressure:-
●Normal range: 10–21 mmHg

●Mean: 15–16 mmHg

●Variation: Diurnal (Morning > Evening by 3–6
mmHg)

5. Importance of IOP Measurement:-

●Detects glaucoma early.
●Monitors response to therapy.
●Assists in postoperative evaluation.
●Helps in diagnosing ocular
hypertension or hypotony.

6. Factors Affecting IOP:-
●Age
●Posture
●Heart rate, blood pressure
●Time of day
●Eye rubbing, squeezing
●Medications (steroids increase IOP)

7. Classification of Tonometers:-
1. Indentation tonometers (e.g., Schiötz)
2. Applanation tonometers (e.g., Goldmann,
Perkins)
3. Rebound tonometers (e.g., iCare)
4. Non-contact tonometers (NCT)
5. Dynamic contour tonometer

8. Schiötz Tonometer – Introduction:-

●Most common indentation tonometer.

●Invented by Hjalmar Schiötz (1905).

●Used to measure IOP by indentation of cornea.

10. Schiötz Tonometer – Parts:-

●Plunger.
●Footplate.
●Scale & pointer.
●Weights (5.5g, 7.5g, 10g, 15g)
Handle.

11. Schiötz Tonometer

12. Schiötz Tonometer – Procedure:-
1. Patient lies supine.
2. Instill topical anesthetic.
3. Place tonometer vertically on cornea.
4. Note scale reading.
5. Convert reading into mmHg using
conversion chart.

15. Schiötz Tonometer –
Advantages:-
●Simple and inexpensive.

●Portable.

●Useful for mass screening.

16. Schiötz Tonometer –
Disadvantages:-

●Contact method → risk of infection.
●Requires supine position.
●Corneal thickness affects reading.
●Less accurate in irregular cornea.

17. Applanation Tonometry –
Principle:-

Based on Imbert-Fick Law:
●Force required to flatten (applanate) a fixed
area of cornea indicates IOP.

19. Types of Applanation Tonometers:-
●Goldmann Applanation Tonometer (GAT)

●Perkins Handheld Tonometer

●Tono-Pen

●Maklakoff tonometer

21. Goldmann Applanation Tonometer –
Introduction:-
●Gold standard for IOP measurement.

●Mounted on slit lamp.

●Measures force to flatten 3.06 mm corneal
area.

24. Goldmann Tonometer – Procedure:-
1. Use fluorescein dye and topical
anesthetic.
2. Align blue cobalt light.
3. Adjust prism until two semicircles just
touch.
4. Read IOP on drum scale (in mmHg).

26. Goldmann – Advantages
●Highly accurate.
●Most widely used.
●Minimal effect of corneal rigidity.
Goldmann – Disadvantages
●Contact → requires sterilization.
●Affected by corneal thickness.
●Needs slit lamp setup.

27. Perkins Tonometer
●Portable version of Goldmann.
●Handheld, battery-operated.
●Used in bedridden or pediatric patients.
Tono-Pen
●Digital, handheld applanation tonometer.
●Requires minimal contact area.
●Displays digital IOP value.

28. Perkins tonometer Tono-Pen

29. Perkins tonometer

30. Non-Contact Tonometer
(NCT):-
●Known as “Air-Puff” tonometer.
●Uses puff of air to flatten cornea.
●No anesthesia needed.
●Ideal for screening & children.

31. Non contact tonometer (NCT)

32. NCT – Advantages
●Non-contact, no infection risk.
●Quick & automatic.
●Comfortable for patient
NCT – Disadvantages
●Expensive.
●Less accurate at extreme IOP values.
●Influenced by corneal thickness.

33. Rebound Tonometer (iCare):-

●Uses small magnetic probe that
rebounds off cornea.
●No anesthesia needed.
●Portable and easy for home or
pediatric use.

34. Rebound tonometer

35. Dynamic Contour
Tonometer (Pascal):-
●Measures IOP independent of corneal
thickness.
●Sensor tip matches corneal contour.
●Gives true IOP and ocular pulse
amplitude.

36. Dynamic contour tonometer

37. Sources of Error in Tonometry:-
●Improper calibration
●Thick/thin cornea
●Poor fixation
●Excessive fluorescein
●Patient squeezing or blinking

38. Precautions (Do’s and Don’ts):
Do’s:
●Clean prism before/after use.
●Use correct alignment.
Don’ts:
●Don’t apply excessive pressure.
●Don’t use unsterile instruments.

39. Clinical Interpretation
●IOP <10 mmHg: Ocular hypotony.
●IOP >21 mmHg: Ocular hypertension.
●IOP >30 mmHg: Risk of optic nerve
damage (Glaucoma).

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