goldman applanation tonometry

TONOMETRY

H.Kangari O.D.

TONOMETRY/H.KangariO.D. 2

Different technique in measurement of the Intra Ocular Pressure(IOP):

Goldmann Applination Tonometry Perkins Tonometer Non-Contact Tonometry Digital Evaluation


Goldmann Applination Tonometry is the most accurate method of measuring Intraocular Pressure.

Measuring the intraocular pressure is important in diagnosis and management of Glaucoma and Ocular Hypertension.


CONTRAINDICATIONS TO IOP MEASUREMENT WITH GOLDMAN TECHNIQUE

1)Active Infection 2)Patients with recurrent corneal erosions 3) Corneal abrasions that are not totally

healed


The Intraocular Pressure is determined by the amount of force required to flatten a constant corneal surface area


Major components of the tonometer

1)Contact Prism 2)Contact Probe 3)Housing 4)Calibrated

measuring drum 5)Tonometer Arm


CHECKING THE INSTRUMENT To calibrate the instrument a control weight bar is

used. Only a trained technician can calibrate the tonometer.

To grossly check the calibration: Turn the measuring drum below zero (the arm

should move backward) Then turn the measuring drum past the zero mark

and the arm should move forward. The arm should move in the same degree in both

direction, above and below the zero mark.


PROBE STERILAZATION

Always clean the tonometer probe before and after each use.

Remove the probe from contact holder (hold the arm before you remove the probe)

Wet a tissue with alcohol and apply to probe in a circular fashion for 5 seconds.

Rinse the probe with Saline Solution and blot dry with a tissue.


PROBE STERILAZATION

OR insert the probe into Hydrogen Peroxide 3% for 5 to 10 minutes.

Rinse the probe with Saline Solution and blot dry with a tissue.


CLEANING & STERILIZING THE PROBE

some factors to be considered such as the following:

(1) 3% H2O2 will ruin the probes in a short period of time and if not properly dried can cause marked pain and a secondary anterior uveitis that is very difficult to resolve. Minimum of 5 minutes maximum of 10 minutes.

(2) 70% Isopropyl alcohol will also destroy the probes and if not properly dried can also cause marked pain and a secondary anterior uveitis that is very difficult to resolve.

When Using Either Of The Above Recommended Procedures Make Sure You Always Rinse The Probe Thoroughly With Saline Solution Then Dry It Completely Before Using It On The Patient's Eye. Never Leave The Probe In The Hydrogen Peroxide For Longer Than 10 Minutes.


Hold the arm, while inserting the probe.

ALIGN the probe- if the patient has less than 3.00 D of astigmatism, position the probe so that the patient’s minus cylinder axis is aligned with the WHITE LINE on the prism holder.


ALIGN the probe- if the patient has greater than 3.00 D of astigmatism, position the probe so that the patient’s minus cylinder axis is aligned with the RED LINE on the prism holder.

KEEP in mind, as you rotate the probe according to cylinder axis the mires will tilt with the direction of axis.


PATIENT PREPARATION

After you have completed a full refractive, binocular and slit lamp evaluation proceed to tonometry.

Anesthetize the cornea. Inform the patient that you are going to put a drop in their eye which will burn and their lids will feel heavy afterwards.

Place a drop of Tetracaine 0.5% in each eye Wet a strip of fluorescein with sterile saline and

place it is superior or inferior bulbar conjunctiva.


Position the patient comfortably at slit lamp.

With the COBALT BLUE filter scan the cornea

Place the measuring drum at 10 mmHg Use Low Magnification


Give proper instructions to the patient: “ I want you to keep your forehead and Chin in

the rest all the time. I want you to look at this point ( based on the eye being tested give an appropriate place for the patient to look at ). Keep your eyes open as wide as you can and try not to blink. I am going get close to your eye with this blue light.


APPLINATION

From the outside instrument get as close as you can to the cornea and center the probe on the cornea.

If you now look in through the microscope, you will see two faint blue mires (semi circles)

If you don’t see this, AGAIN center the probe from the outside of the instrument.


When you see two faint mires, move in the instrument with the joy stick to touch the cornea.

When you touch the cornea, the mires will turn fluorescent green.


If semicircles move freely with the rotation of the measuring drum, the initial contact is correct.


The width and height of two rings must be equal and centered in the field of view.

Rotate the measuring drum, until the inner borders of two semicircles just touch.


Back off the tonometer and read the pressure from the measuring drum.

The scales of measuring drum is marked from 0-8 grams of force. To convert to mmHg, multiply the result by 10.

After completion of the procedure, reevaluate the corneal integrity with cobalt blue light.


Correct position of mires when measuring the IOP


If this is the left eye, the contact of the probe is too much to temporal side.

Move the probe to nasal side


Top mire is superiorly positioned.

The probe contact is too inferior.

Move the probe superiorly.


The contact is too low.

Move the instrument upward.


?


Inappropriate contact The instrument has been

moved too much toward the patient.

The mires will not move by changing the drum.

Move backward and reapplinate.


Mires are too thin. Add more flourescein.


After applination, this type of staining is indicate of applying too much force.


DIURNAL VARIATION

Generally, the variation in intraocular pressure over a 24 hour period is considered to be 3 to 5 mmHg with the highest readings being about (6:00 a.m.).

However, there is recent evidence that known glaucoma patient's highest pressure findings are in the afternoon. Therefore, it would be best to monitor any questionable patients. Take diurnal pressure measurements during the day looking for any pressure spikes with variations greater than 5 mmHg. Example: 14 mmHg O.U. @ 8:30 a.m. and 21 mmHg O.U. @ 3:30 p.m. is diagnostic.

Differences in pressure readings between the two eyes of 3 mmHg or more must be questioned, this is not normal.


Latest information:

Intraocular pressures (IOP) following Laser In Situ Keratomileusis (LASIK) and Photorefractive Keratectomy (PRK) are underestimated.

It depends on the patient's Pre-Op refractive prescription and how much tissue needs to be removed. There is about 10 microns of tissue removed per diopter of refractive error. A patient with a refractive error of 3 diopters of myopia will have approximately 30 microns of tissue removed. For this patient the IOP findings would be underestimated by about 2mm Hg and more for higher refractive errors. This underestimation has been reported for Goldmann applanation tonometry. It is an important new finding and appears to be related to changes in corneal thickness. This might help explain normal tension glaucoma where these patients may have thinner corneas.


PERKINS TONOMETER For patients with physical constraints who

cannot be positioned in the slit lamp or bedriden patients Perkins tonometer (a hand held tonometer can be used)


DIGITAL INTRAOCULAR PRESSURE ASSESSMENT This technique is used in those individual,

where the slit-mounted instrument or the hand-held tonometer cannot be used.

In very young children, extremely anxious patient or developmentally delayed individuals.

The firmness of the globe is subjectively evaluated as soft, meduim, or hard. The harder the globe the higher the IOP.


Digital IOP assessment is contraindicated for eyes with a recent history of blunt trauma, penetrating ocular injury, or intraocular surgery.

Sedation might be recommended for more accurate measurement of the pressure.


Ask the patient to look down and gently rest the tip of the fingers on the center of the upperlid


Indent the globe slightly with one finger tip.

The opposite fingertip will rebound slightly


NON-CONTACT TONOMETER

goldman applanation tonometry

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