Lab 3: Goldmann Application Tonometry
What makes up Fluress?
0.25% NaFl (Purpose/Action: staining fluorescence) 0.4% Benoxinate HCL (Purpose/Action: anesthetic) 1.0% Chlorobutanol (Purpose/Action: Preservative) 15% Povidone (Purpose/Action: Wetting agent/stabilizer) Some generic brands of Fluress contain Thimerosal as a preservative, it is known to cause many allergic reactions, so should be avoided if possible. Good alternative for patients with known 'caine allergies.
Give overview on how to perform Goldmann tonometry.
1) Instill the appropriate drops. 2) Put the probe arm into position. 3) Set the measuring drum to 10 mmHg. 4) Make sure the probe clicks laterally into the straight-ahead position when the tonometer is positioned for measurement. 5) Position the slit lamp light source approximately 60 degrees from the eye pieces and temporal to the eye being measured. 6) Open the slit beam to the WIDEST setting and introduce the cobalt blue filter. 7) Set the biomicroscope to 16X and turn the rheostat to the highest setting. It is important to have the probe as brightly lit as possible. 8) AT this time the patient should be PROPERLY POSITIONED behind the slit lamp. (lateral canthus) 9) CRITICAL! Give the patient an appropriate fixation target to ensure the eyes stay in the straight-ahead position. The instruction to the patient may be as follows, "I need you to keep your forehead and chin in the rests at all times. For me to get an accurate measurement, I need you to look straight ahead without blinking. Keep your eyes open wide while I get a close look at your eyes with this blue light." 10) Before actual contact is made, check for gross alignment outside of the slit lamp, the probe should be approximately 3/4" away from the corneal apex. 11) Move the slit lamp forward by pushing the base, keeping the joystick pushed back towards examiner. 12) Approximately 1/2" before corneal application occurs, the reflection of the probe off the cornea will become apparent. This will appears as two pale blue semicircles (ghost mires). Use the joystick and the vertical alignment to center these "ghost mires" so that they are centered in the view and equally divided, always making corrective movements in the direction of the larger mire. 13) Ask the patient to blink fully and look straight ahead, trying to keep their eye wide open. 14) Use the joystick to move the prove towards the corneal apex while maintaining centration of the blue semicircles. Once corneal contact is made, pulsating fluorescent green semicircles will be observed. 15) Small adjustments will probably need to be made here, (always in the directions of the larger semicircle). If the adjustments to be made are minor, stay ON the corneal surface. If the adjustments are significant, pull to probe OFF of the cornea; make the corrective movement and then re-applanate. Keep in mind removal of the probe will result in drying and staining of the cornea, so please do this quickly. 16) While maintaining application on the cornea with one hand on the joystick, use the other hand to rotate the measuring drum appropriately. Turn the drum until the inner borders of the rings touch. 17) Once the measurement is taken, pull the probe off the cornea and applanate the fellow eye. 18) After both measurements are taken, check the corneas for any anterior epithelial abrasions (green glow).
What drop is most commonly used for Goldmann Applanation Tonometry?
A combination anesthetic and fluorescent stain. One of the trade names this combination can go by is Fluress.
What difference in IOP between the two eyes is considered normal?
A difference in IOP between the two eyes is considered normal as long as it is less than 3-4mmHg.
What should NOT be used to clean the probe? Why?
Alochol Acetone UV Radiation Sterilization Immersion in fluid for more than 1 hour Temperature about 60 degrees C The use of the following products/procedures for disinfection will degrade the tip and cause it to fail.
How do you clean the probe?
Always clean probe before and after each use!! 1) Remove measuring prism carefully from holder. You MUST remove the probe prior to disinfection. 2) Clean: Wipe prism clean before rinsing for 30-60 seconds in running, cold water. Wash instrument with mild soap or cleaner and water to remove debris. 3) Disinfect: Immerse in high-level disinfectant: 10 min soak in 3% H2O2 (NSU procedure of choice)(hydrogen peroxide 3% aqueous solution), 10 min soak in 1:10 bleach dilution (Sodium hypochlorite/household bleach 10% aqueous solution), or 20 min soak in 2% glutaraldehyde. 4) Rinse thoroughly in running, cold drinking water (note: rinsing time in water may not exceed 60 seconds). Rinse well with tap water, then saline. 5) Dry with a one-way tissue, clean and soft. Allow to dry. 6) Store: place into container, clean and dry.
How do you properly hold a patient's lids during tonometry?
Brace the upper lid at the superior lid margin with your thumb and push the lid up against the bony orbit. If you apply pressure to globe and not the bony orbit you will artificially increase patient's IOP.
What are the mechanics of the Goldmann tonometer?
IOP is determined by the amount of force needed to flatten a constant corneal surface. The Imbert-Fick Law shows the basis for this law: P=W/A where P=intraocular pressure in grams, W=force applied during applanation, and A=area of application (constant with Goldmann technique)
How do you properly align the probe in the slit lamp?
If the patient has less than 3 Diopters of corneal cylinder, you can align the zero mark along the white line on the holder. If the patient has more than 3 diopters of corneal cylinder, position the probe so the patient's minus cylinder AXIS (meridian with less power) is aligned with the RED line on the prism holder.
At what point in the exam is Goldmann Applanation Tonometry typically performed? Why?
It is typically the last thing we do in an examination prior to dilation. The topical anesthetic will soften the cornea and make vision blurry. Also, this softening effect allows for faster penetration and transmission across the corneal barrier of the mydriatics, hence faster and complete dilation.
What does LASIK and PRK stand for?
Laser-Assisted In Situ Keratomileusis Photorefractive Keratectomy
What should you do if the patient asks you if the tonometer is going to touch their eye?
Legally, if the patient asks if you are going to touch their yes, you have to tell them. But try to tell them after the procedure is over, as you may increase patient anxiety otherwise.
What are complications/contraindications to performing Goldmann Applanation Tonometry?
Ocular infection Large corneal abrasions Epithelial Basement Membrane Dystrophy Trauma Recurrent Corneal Erosion Bullous Keratopathy Band Keratopathy Severe corneal edema
How do you record your IOP measurement?
TA=15mmHg @ 9:00 am OD igt Fluress Information recorded: mmHg for each eye, the time of day, type of drops used, amount of drops used and if the lids were held.
How does LASIK and PRK affect your Goldmann tonometry reading?
The IOP in these patients tends to be underestimated using Goldmann tonometry. It is an important new finding and appears to be secondary to changes in corneal thickness. (10 microns of tissue removed for 1 Diopter of power). This goes for both hyperopic and myopic surgeries. This is a recent development and is of great clinical importance when evaluating these patients as possible glaucoma suspects.
Why would the width of the mires vary? What is the appropriate width of the mires? How would variations in mire width affect the IOP reading?
The width of the mires will vary depending on the amount of fluorescein that is present. The appropriate width is 1/10th the diameter of the flattened area. If the mires are either too wide or too narrow the readings will not be accurate. When the mires are too wide, the reading will be artificially high, and conversely when they are too narrow, the reading will be artificially low.
What is the purpose of Goldmann Applanation Tonometry?
To measure the intraocular pressure (IOP) in mmHg. This can aid in the diagnosis and treatment of glaucoma and ocular hypertension. Goldmann Application Tonometry is considered to be the "gold standard" of IOP measurement.
