Tonometry Procedure

All the details about different types of tonometer and there procedure. Also added some new tonometers.

1. Tonometry-Procedure Name: Shaikh Yusra Rani Course: S.Y.B.Optometry Subject: Optometric Instrumentation Roll no:. 32 Date: 22.05.2019

2. Index Tonometry Factors influencing IOP Direct tonometry Indirect tonometry Other Instruments References

3. Tonometry It is the method of measuring intraocular pressure with the help of an instrument called tonometer. Tonometer’s are divided into: 1) Direct Manometer 2) Indirect (Contains contact and non contact) Static -Indentation Eg. Schiotz , Mercurial, Electronic Schiotz, Scleral, Von graefe -Applanation Eg. Goldmann , Ocular response analyser(NCT), Pulse air(NCT), Perkins, Maklakov , Posner, Draeger, Ocuton (NCT), Grolman airblast , Mackay- marg , Pneumatic, Tono -pen -Rebound Eg. i -care -Trans palpebral(NCT) Eg. Pressure phosphene -Disposable Eg. Tono -safe , Tono -shield -Digital/Palpation Method Dynamic (NCT) Eg. Pascal , Ballastic , Vibrational

4. Factors influencing IOP Rate of aqueous formation Resistance of aqueous outflow Increased episcleral venous pressure Dilatation of pupil Hereditary Age Sex Diurnal variation Postural variation Blood pressure Osmotic pressure of blood Others

5. Direct Tonometry Manometry Principle- Based on hydrostatic equilibrium and is used for measuring the static pressure exerted by a still liquid/gas. Example- Manometer Procedure- Needle is inserted into anterior chamber through a self-sealing, bevelled corneal puncture. Needle is connected to a fluid- filled tubing. Height of the fluid in the tubing corresponds to intraocular pressure. Tubing can also be connected to a fluid-filled reservoir that has a pressure-sensitive membrane. Movement of membrane, recorded optically or electronically, is a measure of intraocular pressure. Advantages- It is used for continuous measurement of intraocular pressure Mostly helpful in experiments and research work Disadvantages- Not practical method for human beings Needs general anaesthesia Introduction of needle produces breakdown of blood-aqueous barrier and release of prostaglandins which alter intraocular pressure

6. Indirect Tonometry Static Indentation/Impression Principle- Based on the fundamental fact that a plunger will indent a soft eye more than a hard eye. Example- Schiotz Tonometer Procedure- Footplate and lower end of plunger should be sterilized. Anesthetize patient’s cornea with paracaine /2-4% topical xylocaine. Patient made to lie in supine position and asked to fixate at the target given on ceiling. Examiner separates the lids and gently rests the tonometer vertically on patient’s central cornea. Reading is recorded as soon as the needle becomes steady. Three readings are taken to get the average value. In the end tonometer is lifted and a drop of antibiotic is instilled. Customary to use 5.5g weight initially. If scale readings are below 3 then add 7.5g/10g as indicated. Conversion table is used to derive intraocular pressure in mmHg from scale reading and plunger weight. Advantages- Portable, Sturdy, Inexpensive, Easily operated and easy to clean and maintain

7. Doesn’t require power source/slit-lamp Disadvantages- False IOP -> Ocular rigidity Cannot be used in traumatic/post operative/corneal disease cases Applanation Principle- Based on limbert-fick law which states that pressure inside the sphere (P) is equal to the force required to flatten its surface (F) divided by the area of flattening (A) Example- Goldmann tonometer Procedure- After the patients cornea is anesthetized by 2% xylocaine and staining of tear film by fluorescein is done, he is then made to sit in front of the slit lamp (Cobalt blue filter) Bi-prisms are advanced until its apex just touches patients cornea At this point 2 fluorescent semi circles are seen through prism, we adjust the applanation force until the inner edges of the 2 semi circles just touch, this is the end point. IOP is determined by multiplying dial readings with 10. (Readings obtained are in “g” so to convert into “mmHg”) Advantages- Most accurate No indentation, so not much force is applied on cornea Doesn’t get affected by corneo -scleral rigidity Can be done on post operative/injury cases Disadvantages- Need slit lamp, dark room and staining

8. Rebound Principle- Based on rebound measuring principle, in which a very light weight probe is used to make a momentary contact with the cornea. Example- i -care Procedure- Since local anaesthesia lowers the tonometry readings, it is not used. Ask patient to relax and fixate at point straight ahead. Bring the tonometer to patients eye such that the central groove should be in a horizontal position, and the distance from the eye to the front part of the collar should be the length of the collar. (distance between tip of the probe to the patients cornea should be 4-8 mm) Press the measurement button lightly without shaking, tip of probe should make contact with centre of cornea and 6 measurements are taken giving IOP digitally. Advantages - Accurate, not painful i.e , very gentle More patient compliance Disadvantages- May give error when not properly placed or shaken while measuring Probe can fall out when tonometer is facing downward Trans-palpebral Principle- Based on determining the acceleration of a free falling rod with a definite weight and its interaction with the elastic eye surface through eyelid. Example- Pressure phosphene tonometer Procedure- No sterilization is done to the instrument as there is no contact of the instrument with the patient. Spring end presses on eyelid until patient sees phosphene and then device is removed. Pressure at which phosphene was seen is recorded on scale and represents IOP

9. Advantages- Can be used for young children For severely developmentally challenged patients Portable, can measure own IOP Disadvantages- Cannot be used for patients with scleral rigidity Thickness of the eyelids may induce error in readings Disposable Principle- Example- Tono -safe tonometer Procedure- Advantages- Portable, lightweight and easy to use Can be used for self measurement Disadvantages- Can become infective causing bacterial infections

10. Digital Method Principle- Based on palpation by the examiner Procedure- IOP is estimated by response of eye to pressure applied by finger tip. Basically an approximate idea about the level of IOP by sense of touch. Advantagges - Gives a rough estimate Useful in non severe cases and when instrument is not available Disadvantages- Not accurate and doesn’t provide digital measurement. Dynamic Principle- 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. Example - Pascal Tonometer Procedure- 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 Advantages- Can be performed for outpatients and patients with sufficient bilateral ocular fixation Disadvantages- Cannot be done for uncooperative patients, poor vision or patient with nystagmus.

11. Other Instruments Static: Indentation: Mercurial, Scleral, Von graefe Applanation: Ocular response analyser(NCT), Pulse air(NCT), Perkins, Maklakov , Draeger, Ocuton (NCT), Mackay- marg , Pneumatic, Tono -pen

12. References Book: Comprehensive Ophthalmology – A.K.Khurana Website: www.google.com www.wikipedia.com www.slideshare.net www.eyewiki.aao.org www.icaretonometer.com www.bjo.bmj.com www.innovamed.com www.researchgate.net www.clinicaltrials.gov www.ajo.com

13. Thank You! -Yusra-