Fluress© will be used in this procedure, it contains a stain and anesthetic, which allows applanation of a defined area of the cornea with a variable force. Goldmann tonometry is the last thing you do before dilation. Why? Because the topical anesthetic will soften the cornea and can make vision blurry. However,this softening allows for faster penetration and transmission across the corneal barrier of the mydriatics, hence, faster and more complete dilation. The applanation of the cornea, which is ever so light, will slightly distort the cornea and for a short period cause blurred vision. The main point being addressed is, "make sure you know the patient's final Rx," otherwise it will be too late to refine after Goldmann tonometry. Goldmann tonometry is the "Gold Standard" by which all other tonometry is compared. The upper "suspect reading" for Goldmann tonometry is equal to or greater than 21 mmHg.
Fluress©

Contains	Purpose or Action
0.25% Sodium Fluorescein	Staining Fluorescent Agent
0.4% Benoxinate HCl	Anesthetic
1.0% Chlorobutanol	Preservative
15% Povidone	Wetting agent and stabilizer, preventing precipitation when Sodium Fluorescein and Benoxinate HCl are combined together in a solution

NOTE:There are generic brands of Fluress© that contain proparacaine HCl, but have thimerosal as a preservative. Thimerosal must be avoided it causes a number of allergic reactions (e.g., diffuse superficial punctate keratitis, corneal infiltrates, lid and conjunctival edema, conjunctival injection, etc.).

AREA OF APPLANATION

The diameter of the circular zone of applanation is 3.06 mm. Hence, one can calculate the area of that circular zone of applanation.

Area = (r)² = 3.1416 x (1.53)² = 7.3542 mm²

This has been found to be the minimal area of applanation needed to give accurate results, yet, causing only an increase of 2.5 percent in intraocular pressure. Example: 20 mmHg, which is just 1 mmHg below the suspect reading of 21 mmHg (20 mmHg x 2.5% = 0.5 mmHg). Accordingly, the intraocular measurements should be accurate to within + or - 0.5 mmHg for intraocular pressures of 20 mmHg or less. Remember, tonometry findings are not always diagnostic of glaucoma, but just one of several findings you must consider. There is a condition called ocular hypertension, when the patient's intraocular pressures (IOP) run over 21 mmHg, but have no optic nerve head or visual field changes. These patients indeed need close monitoring for any changes in their fields or optic nerve heads.

Visual fields and careful evaluation of the optic nerve heads and the retinal nerve fibers are extremely important in diagnosing glaucoma. If I had to pick one of the above as the most important finding in predicting the possibility of a patient having glaucoma I would have to say the appearance of optic nerve heads and retinal nerve fiber layer. One cannot be too dogmatic for a patient's visual fields, optic nerve heads, and nerve fiber layer are so very closely related.

ORDER OF DIAGNOSTIC IMPORTANCE
1.) Appearance of the optic nerve heads and nerve fiber layer
2.) Visual fields
3.) Intraocular pressures (IOP's)

It is somewhat interesting how the area of applanation relates to the calculation and conversion from grams to mmHg. Pressure is equal to force per unit area but one must factor in the density of mercury (Hg) which is 13.6 gm/cm3. One could say 13.6 gm/cm³ of Hg.

Conversion to mmHg
Pressure = Force/Area
Pressure = 1 gm / .073541714 cm² x 13.6 gm/cm³ of Hg
Pressure = 1 gm x cm³ of Hg / .073541714 cm² x 13.6 gm
Pressure = 1 cm of Hg / 1
Pressure = 1 cm of Hg = 10 mmHg

Therefore, one gram of force is needed to flatted an area equal to .073541714 cm² when the eye contains a pressure of 10 mmHg and 2 gms when 20 mmHg, etc. Each large number on the micrometer is in grams; 1 gram equals 10 mmHg while each small mark in between is equal to 2 mmHg.

CLEANING & STERILIZING THE PROBE

The FDA and CDC recommendations are in your manual, however, there are 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.

TONOMETRY PROCEDURE

It is important you inform the patient what you are going to do and why. You do not have to go into great detail other than you are going to check the pressure of their eyes or simply "this is the blue light glaucoma screening test". If the patient should ask if you are going to touch their eye reply, I am going to use drops to numb the front surface of your eye, the instrument will gently touch the tear film of your eye and because of the drops you will feel nothing. Once you have completed the procedure you need to tell the patient your findings, e.g., "The test indicates the pressures are normal."

(1) Set the measuring drum on one (1 gm) equals 10 mmHg make sure to align the white line on the probe carrier with the zero or 180 degree marker of the probe.
(2) Place the light source 60 to 65 degrees temporal to the probe.
(3) Use wide open diffuse illumination, bright illumination, cobalt blue filter and 16x magnification.
(4) This should go without saying, but you always align the patient just like you would before starting a normal slit lamp examination.
(5) Make sure the patient keeps their head tightly against the head rest. Complete steps 8 & 9 then (pull the slit lamp back, shut it off, and lock the slit lamp in place.)
(6.) Always ask the patient if they have ever had a reaction to Novacaine; normally this would be asked during the case history. If they are you should use Proparacaine HCl and a fluorescein strip. If not place one drop of Fluress© O.U. an give the patient a tissue to blot their eyes. Place the bottle on a flat surface away from you and the patient. If you spill or drip Fluress© on yourself or the patient's clothing it is almost impossible to get out.
(7.) Always tell the patient not to rub their eyes. They may blot, but not rub for a least 20 minutes.
(8.) The optical system and tonometer are "not aligned" and must be offset by 5 to 10 degrees. The view of the probe and mires are seen only with one eye.
(9.) Pre-alignment is done from outside the slit lamp, tell the patient where you want them to look.
(10.) Just before you are ready to move the slit lamp forward have the patient blink then open their eyes very wide. When the probe just touches the cornea you'll see a limbal glow, stop, you have advanced it far enough. You will see the mires through the slit lamp at this point.
(11.) If, however, you advance the probe too far forward or have too high of magnification you may see nothing.
(12.) If the mires are too wide the readings will not be accurate. Pull the slit lamp back dry off the end of the probe. (Lashes in contact with probe, too much Fluress© or excessive tearing are the most likely cause) then start over.

You do not have to pull the probe off the patients eye to make fine adjustments for alignment; this can be done with small movements while on the cornea. Removing the probe from the patients eye then putting it back on until you have proper alignment will result in drying and staining of the cornea.

 

 

Recording Your Findings

OD 18 mmHg = right eye

T_A Goldmann @ 9:30 a.m. i gtt Fluress© O.U.

OS 18 mmHg= left eye

If a patient wears soft lenses you should flush the eyes out very well, cleaning the patient up to remove all the fluorescein, then advise them not to wear their lenses for at least one (1) hour. Fluorescein will be absorbed into the soft lens turning it yellow. Patients who wear hard lenses should be advised not to wear their lenses as long as they would normally. Topical anesthetics soften the cornea's epithelium making an abrasion more likely. All patients should have has much of the fluorescein dye cleaned off as possible.

If the corneal astigmatism is greater than 3.00 Diopters the measurement is made 43 degrees from the meridian of the lower power. It has been found that on very toric corneas placing the probe offset by 43 degrees gives an area of applanation closest to 7.35 mm².

EXAMPLE: 41.00@30 degrees and 45.00@ 120 degrees

You would place the red line on the probe carrier @ the 30 degree mark on the probe. The red line and the white line on the probe carrier are separated by 43 degrees.

TOPICAL ANESTHETICS

Generic / Company	Time Of On Set	Duration
0.5% Proparacaine HCl	13 to 15 Seconds	15 Minutes
(Opthaine)	1+ Stinging Reaction	1+ Punctate Keratitis
0.4% Benoxinate HCl	15 Seconds	15 Minutes
(Dorsacaine)	2+ Stinging Reaction	2+ Punctate Keratitis
0.5% Tetracaine HCl	15 Seconds	15 to 20 Minutes
(Pontocaine)	3+ Stinging Reaction	3+ Punctate Keratitis

Keratitis: Corneal staining and loss of epithelial cells, toxic in nature

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. There are several conditions which must be considered when this occurs.
(1) Glaucoma
(2) Retinal Detachment
(3) Uveitis-Iritis
(4) Poor Technique (This of course it not an acceptable answer!)
Three are known conditions resulting in, possible, diagnostic pressure differences between the two eyes. Initially, the IOP's are lower in the affected eye. It should be pointed out that in the later stages of a uveitis the pressure may possibly become higher in the affected eye.

It is not uncommon when the probe is in contact with the eye to see the fluorescein patterns pulsate, this is caused by the venous pulsation within the eye. There are differences of opinion when these pulsating mires should be interlocked and the pressure reading interpreted. It is my opinion, they should be interpreted when they are at the highest point if the patient is a possible glaucoma suspect. If the pulsation is significant, you can adjust the micrometer so the semicircles pulsate equally to either side of the correct endpoint. Some doctors take two readings one at the high end and another at the low end then average the two readings. Recording both the high and low readings and the average.

Venous pulsation is a very important finding and should always be recorded, even if it has to be induced. Lack of venous pulsation or the ability to induce it should make one think of either (1) the intraocular pressure is higher than the venous pressure or (2) the intracranial pressure is higher than the venous pressure. This will be discussed in more detail at a later date.

CONDITIONS OF CONCERN/CAUTIONS

1.) Patients with recurrent corneal erosions (be very careful)

2.) Bullous keratopathy (depending on the severity)

3.) Corneal abrasions that are not totally healed (be very careful)

4.) Edematous corneas (be very careful)

5.) Band keratopathy (depending on the severity)

Take three (3) readings on each eye, later one (1) will usually be enough when you are in practice. This is mainly to force you to become more confident and competent when working around patient's eyes. Like most things the more often you do something the better you are at interpreting your findings. You need to examine the corneas to see if you caused any disruption or left a toe mark from the probe. If there is considerable staining you should give the patient some artificial tears to be used "prn" (or as needed) should they notice any irritation.

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.

One last thing, make sure you always take the time to clean all the Fluress© or fluorescein off from around your patients' eyes. Nothing looks worse than to see a patient walking down the clinic hall or out of the building with this yellow stain all around their eyes. Remember if you get (Fluress© or fluorescein) on you or your patient's clothing it's almost impossible to get out (please, be careful out there).

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