1. TONOMETER

2. Intoduction
Definition: A tool used to measure the pressure of the eye.
A tonometer is used to help detect glaucoma.
A tonometer measures the production of aqueous humor, the liquid found inside the eye, and the rate at which it drains in to the tissue surrounding the cornea.
Tonometry is the procedure performed to determine the intraocular pressure (IOP)

3. History: 1826:  William Bowman used digital tonometry as a routine examination test.
1863: Albrecht von Grafe designed the first instrument to attempt to measure intraocular pressure.
Further instruments followed, notably by Donders in 1865 and Preistly-Smith in These instruments were all of the indentation type and rested on the sclera (no anaesthetic was used until 1884).
1885: Maklakov designed an applanation tonometer. This was refined in Used for a number of years in Russia and Eastern Europe. This was used till 1959.
1905:  Hjalmar Schiotz produced his indentation tonometer. This made tonometry a simple and routine clinical test.

4. Albrecht von Grafe tonometer
Donders tonometer

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

6. Intraocular pressure (IOP) is the fluid pressure inside the eye
Intraocular pressure (IOP) is the fluid pressure inside the eye. Tonometry is the method eye care professionals use to determine this.
IOP is an important aspect in the evaluation of patients at risk from glaucoma. Most tonometers are calibrated to measure pressure in millimeters of mercury (mmHg).
Eye pressure is measured in millimeters of mercury (mm Hg). Normal eye pressure ranges from mm Hg, and eye pressure of greater than 22 mm Hg is considered higher than normal. When the IOP is higher than normal but the person does not show signs of glaucoma, this is referred to as ocular hypertension.
High eye pressure alone does not cause glaucoma. However, it is a significant risk factor.
Individuals diagnosed with high eye pressure should have regular comprehensive eye examinations by an eye care professional to check for signs of the onset of glaucoma.

7. Ideal tonometer Should give accurate and reasonable IOP measurement
Convenient to use
Simple to calibrate
Stable from day to day
Easier to standardise
Free of maintenance problems

8. Factors modifying IOP with respiration and heart beat
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

9. Continue dilatation of the pupil
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

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

11. Continue
Digital tonometry

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

13. Commercially available instrument
Goldmann tonometer
Parkines hand held tonometer
McKay-Marg tonometer
Schiotz tonometer
Air puff
tono-pen

14. Instruments
applanation tonometer

15. Continue
Parkines Tono-pen Schiotz

16. Continue
Air puff

17. 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

18. continue
It based on Imbert-Fick law - it states 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

19. Procedure patients counseling
dry, clean tonometer probe should 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

20. continue 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

21. 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.

22. contraindication
Head trauma
suspicion of ruptured globe
narrow angle

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

25. Tono-pen fully portable held in any position operated by index finger
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

26. 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

27. continue
used with patient in any position
portable

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

29. continue
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 non-infectious condition

30. 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

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

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

33. Non-contact tonometer
Air-puff tonometer

34. continue 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.

35. Continue 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.