Tonometry

1. Nishita afrin B.Optom 3 rd batch ICO Tonometry

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 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

5. Continue 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.

7. Continue Digital tonometry

8. continue Instrumental tonometry contact non contact tonometer 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

12. Continue Perkin’s tono -pen schiotz

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

15. continue 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

17. 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

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

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

21. 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

22. 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

23. continue used with patient in any position portable

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

25. continue Principa l : 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

26. 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

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

28. 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

29. Non-contact tonometer Air-puff tonometer

30. 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.

31. 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.

32. THANK YOU