Tonometry.4

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Tonometry

Chapter 4Lecturer : Dr. Genalin Ang O.D.


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This is a clinical technique that provides ameasurement of the Internal pressure of theeye Called IOP ( Intra ocular pressure, ocular

Tension )

What is tonometer?


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High intraocular pressure causes damage tothe optic nerve, which can lead to glaucoma.But what is it? What makes it happen? Whatcan you do about it?

First, let's dissect the term.Intra is the Latin word for within or inside.

Ocular refers to the eye.Pressureis the result of applying a force

onto a surface.

What is IOP ( IntraocularPressure)


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Small reductions or increases in ballpressure would mean that the

bounce potential would change andinfluence three key dimensions ofthe game: height of return after theball strikes the floor, bounce off the

backboard, and bounce off the rim ofthe basket.


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HOW DOES THIS APPLY TO THEEYE?

The aqueous humor is confined to asmall space in the front part of theeye. The remainder of the eye isfilled with vitreous humor.


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When we talk about intraocular pressure, weare referring to the pressure exerted bythese two fluids on the walls of the eye andon the structures inside.

Similar to the basketball, the materials of theeye that contain the aqueous and vitreoushumors in a closed space have limitedflexibility and expansion capabilities. Thismeans that additional aqueous humorintroduced into the eye increases thepressure inside the eye.


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There is three different principles :

APPLANATIONIDENTATIONMANOMETRY

Theoretical Principle ofTonometery


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Is the most commonly used technique tomeasure IOP

IOP= force/ areaMeaning in physics + force applied as well as

the size of the area of the eye on which thisforce applied

Applanation


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GOLDMANN

PERKINS

NON-CONTACT ( NCT ) TONOMETERS

APPLANATION


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Goldmann Tonometer


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Goldmann tonometerthe "gold standard" instrument attached to

the slit lamp biomicroscope used in all eyedoctors' offices

It requires a cobalt blue light source and asmall droplet of fluorescein on the ocularsurface.

Applanation


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A tiny pressure sensor attached to a spring-loaded arm is gently placed against the tearfilm, and the doctor or technician reads thepressure through the microscope under the

blue light.

Applantion


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Maklokov TonometerIs a method of applanation that applies a

constant force to the cornea


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Schiotz tonometer

Indentation


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DisadvatagesMore invasiveIt is affected corneal rigidity

Repeated measurement may be misleading due to aqueous humour being evacuated ateach reading

Schiotz tonometer


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Is the most direct and accurate method tomeasure IOP

Its not use due to invasive nature of theprocedure

Manometry


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Goldmann Tonometer

Common Techniques


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Goldmann applanation tonometry isconsidered the Gold Standard based onits accuracy and repeatability ofresults. A hand-held version called the

Perkins tonometer

Goldmann Tonometer


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Excessive pressure reading on the eye distortsthe mires Turning the reading drum

Figure 4.4 a) Move Slit lamp up b) Move

slit lamp rightc) Move slit lamp up and left

I ffi i h


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Insufficient presurre on the eyeon indenting the probe


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Advantage you can use in different position

Perkins Tonometer


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Using Perkins tonometer


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Uses both Applanation and Identationpriciple

Portable, penshape hand held deviceshandheld device and calibrates digitally with

the push of a button. It requires a disposablesterile cover for each patient. The steriledevice tip is gently placed against the tearfilm by the doctor or technician, and thepressure reading appears on

Tonopen


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Tonopen


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Advisable in Children , un cooperativepatients or patient unable to be positionedbehind the lamp or long enough to performPerkins or NCT

Contraindicated in patients with knownallergies to latex.

Tips of Tonopen


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Which generally requires no anesthetic drop,is widely used in doctor's offices, clinics, andscreening facilities. It is very safe due to the"no touch" technology,

Non Contact Tonometry


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Non Contact tonometer

G ll NCT i


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A video monitoring system to view the imageof the eye

- Some sort of visible mires in the viewer(reflections off the cornea)

Mires must be focused and aligned- A button on the joystick is pressed (or an

automatic mechanism is triggered) and theinstrument shoots its puff of

air- The reading is visible in the viewer (can

also be printed on some models)

Table-

Generally, most NCT instrumentsuse the following elements andsteps:


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Different types of NCT


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When applicable, the chin and headrest ofthe instrument must be disinfected

Demonstration the small air puff onto thepatients fingers

By convention, the right eye is usually testedfirst

If applicable, a safety lock usually allowsthe instrument to stop at a safe distancefrom the eye

Tips fro NCT


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3 readings or more are taken and averaged(to account for ocular pulse)

NCT readings are often imprecise and arebest used as screening tools or if corneal

contact is not possible.Goldmann or Perkins tonometry should be

performed whenever possible, and each timean NCT measurement is

abnormal or suspicious


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Schiotz tonometer


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The patient is placed in a supine position forthe procedure. A constant known weight isapplied to the cornea and the depth of thearea

depressed is measured and converted to IOPby using a graph.

Readings are placed on a calibration scalefrom which the IOP is determined

The measurement is then corrected for errorinduced by corneal rigidity on a graph.


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For high IOP measurements, it is necessaryto use more weight to perform Schiotzbecause there is more resistance toindentation. The additional weight is needed

to indent the cornea and obtain an accuratereading. The

disadvantages of the Schiotz include: highrisk of corneal abrasion, supine position of

patient, influence of technique onresults, assembly and disassembly of

instrument, aqueous displacement affectingrepeat readings, and patient

apprehension to procedure. Since there are

Tips


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Finger Tension ( DigitalIOP )


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Finger tension IOP is a crude method togrossly assess IOP used in situations whereno other more precise method is

available or possible (e.g. Non-cooperative

patients). One can only approximate whetherthe eye is soft, normal or hard

and compare both eyes for a notabledifference.

Finger tension IOP


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The IOP value for each eyeType of anesthetic and instrument usedThe time that tonometry was performed. Repeated measurements and their time (if

performed) Patient position (if pertinent)

Recording


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Normals IOP

The mean IOP in the normal population is16mmHg +/- 2.5mmHg

Interpretation of Results


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Physical factorsPhysiological factors

FACTORS INFLUENCING IOP


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Pressure on the globe

Applying pressure on the globe tends toelevate the IOP. This is important becauseduring the procedure it may becomenecessary to control the patients lids

Physical factors


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Patient blinking also results in an increase inIOP. Forceful blinking or blepharospasm cansignificantly elevate the

IOP due to lid muscle compression on the

globe. It is therefore necessary to instructpatients to blink gently to

avoid an artificially elevated measurement.

i fl i


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Trauma or inflammation of the eye can eitherdecrease or increase the IOP.

If trauma affects the ciliary body, aqueousproduction may be reduced which woulddecrease the IOP while if the trauma affectsthe anterior chamber angle structures,aqueous outflow may be reduced which

would increase the IOP.

Trauma / inflammation


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If a patient has an intraocular inflammationsuch as uveitis, the ciliary body may becomeinflamed and decrease aqueous productiontherefore decreasing IOP.


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Certain medications may elevate or reduceIOP

Long-term use of corticosteroids (especiallytopical and oral) has proven to induce

increased IOP. Certain blood pressure medications such

as Beta-blockers when taken orally canreduce IOP.

The use of substances such as marijuanaand alcohol temporarily reduce the IOP.

Medication


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Diurnal variation

Vascular Integrity

Physiological factors


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The IOP tends to vary throughout the daybeing generally highest during the morningand lowest in the evening.

The average diurnal variation is 4mmHg.

Persons with glaucoma tend to have agreater diurnal variation. Diurnal

variation exceeding 8mmHg is a risk factorfor POAG. To measure diurnal variation in IOP

several measurementsmay be taken at various times of the day in

order to make a definitive assessment.

Diurnal Variations


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Impaired venous drainage in the head-neckregion can result in a decrease of aqueousoutflow and subsequently

an increase in IOP up to 4-5mmHg. This can

be brought on by a tight collar or when thepatient holds their breath

during tonometry.

Vascular Integrity


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If there is poor circulation to the ciliary body,then aqueous production is reduced and IOPis decreased. This may occur in persons withcardiovascular conditions, including carotid

occlusive disease. When there is carotidartery


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When the patient is in a supine position or ifthe head is below the heart, IOP is increased.

The IOP is measured tobe 2-3mmHg higherlying down than when the patient is sitting

upright. The increase in IOP can beattributed decrease the aqueous outflow.

Patient Position Movement


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Thank You

The most pathetic person in the world issomeone who has sight, but has no vision. Helen Keller

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Tonometry.4