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TONOMETRY

Manasa.N

2yr BS.c optometryNSO

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CONTENTS Introduction Indentation tonometry

Schiotz tonometer Applanation tonometry Goldmann tonometer Perkins tonometer

Tonopen Mackey marg tonometer Non contact tonometer

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What is a tonometry??? Tonometry is the procedure, eye care

professionals perform to determine theintraocular pressure (IOP).

It is used to determine the pressure inthe eye by measuring the firmness of itssurface.

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Why it is done.?? This test is used to check for Glaucoma.

Glaucoma;

Is an eye disease that can cause blindness by

damaging the Optic nerve.

Normal IOP ranges from 10 to 21mmHg

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Indentation tonometry If a plunger of

known weight isrested on thecornea, the depth ofplunger indentationshould (?) be

proportional to IOP.

Plunger is connectedto lever arm and

scale.

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Schiotz tonometer The footplate is

rested on the corneaand the plunger isfree to indent thecornea.

A variety of weightsmay be used tominimise errors dueto corneal rigidity.

(use with tables)

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Simple

technique Portable

No need for SL

Reasonablypriced

Cornealabrasions more

likely.

Effect of corneal

rigidity onreading

Advantages Disadvantages

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Applanation tonometry

Basis : Imbert-fick law.

For an ideal dry, thin walled sphere, thepressure inside the sphere (p) is equalsthe force (F) required to flatten itssurface, divided by the area offlattening (A):

P = F/A or F = PA

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Applanation tonometer Goldmann - The pressure which is

required to flatten the cornea gives the

IOP only if the applanated cornearanges from 2.5 to 4 mm.

It is in this range that the adhesiveforces of tears and the force necessaryto overcome the rigidity of the cornea

are in balance.

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A Goldmann Tonometer

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Slit lamp of goldmanntonometer

Mires seen duringgoldmann tonometrythrough slit lamp

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Easy to use

cheap comfortable

(apart from

anaesthetic)

Quick

Need foranaesthetics

Cannot bedelegated

Contact with

cornea (slightchances ofabrasion

Advantages Disadvantages

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Perkins Tonometer It uses the biprism as the Goldmann

applanator.

The light source is powered by battery,and a counter balance enables theinstrument to be used in both the

vertical and horizontal positions.

The readings are consistent andcompare quite well with the Goldmannapplanator.

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Perkins tonometer The readings are

consistent and

compare quite wellwith the Goldmannapplanator.

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Tonopen Tonopen measured an average of 1.7

mm higher than the Goldmann

tonometer.

Easier to use with corneal

abnormalities.

Patient can be lying or sitting.

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Tonopen A sterile cover must

be over the tip.

Ensure patient hasanaesthetic, gentlytap tonopen againstcornea.

Final averagedreading (of usually 4 6) is displayed

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Mackay-marg tonometer It applanates the cornea via a plunger that moves

within a sleeve, similar in fashion to a Schitztonometer.

The plunger is electronically coupled to a transducerand graphically records the movement of the plungeron a moving strip of paper.

The plunger first indents the cornea recording on thegraph paper, the sum of the force required to flattenthe cornea and the IOP.

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Mackay-marg tonometer The pressure tracing then decreases to a level that

represents the IOP.

Because the tonometer records instantaneously,multiple readings should be averaged in order toadjust for fluctuation in pressure due to the ocular

pulsation.

It is especially useful in edematous or irregularcorneas.

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Non contact tonometer Noncontact (or air-puff) tonometry does

not touch your eye but uses a puff ofair to flatten your cornea.

This type of tonometry is not the bestway to measure intraocular pressure.

But it is often used as a simple way tocheck for high IOP and is the easiestway to test children.

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Non contact tonometer

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Advantages of NCT Corneal applanation is produce by air

pulse.

No topical anaesthetic

No risk of infection

No corneal abrasion

Good for population screening

Good results

Costly equipment

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Questions...???

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Thank you