Tonometry:Special Diagnostics
Applanation tonometry displaces less than _____ of aqueous.
0.5 microliters
Tonometer scale
1 = 10 mmHg 2 = 20 mmHg Each line represents 2 mmHg
Normal IOP
10-21 mmHg
Recording example for goldmann and tonopen the same
1:00pm Ta (right over left): 12mmHg 14mmHg 1:00 pm soft or Tt hard
Pt with family history of glaucoma
30% will be diagnosed with glaucoma
HIGH IOP (Average Glaucoma range)
50-60 mmHg
Average corneal thickness
555 microns
applanation tonometry
A form of tonometry in which the force required to flatten a small area of the central cornea is measured. Ex: Goldman applanation tonometry
Perkins tonometer
A handheld applanation tonometer
Tonopen Advantages
Advantages: can be used for scarred or edematis corneas, fairly quick, portable, lightweight, useful for patients who are hard to position, single use tips.
Pharmacology for Goldmann
Anesthetic and fleuroscein-Follow office protocols
Proparacaine with impregnated Fluorescein strip
Anesthetic with Fluorescein
Tetracaine with Fluorescein strip
Anesthetic with fluorescein impregnated
Types of tonometry
Applanation, indentation, non-contact
Normal aqueous flow (versus glaucoma)
Aqueous fluid flows smoothly through the eye and out, in glaucoma the fluid builds up causing pressure because it doesn't drain well.
Difficulties with tonometry
Astigmatism, Corneal scars, corneal edema, corneal thinning
When centering the prism on the patient's eye, you should __________ before moving it. Small vertical adjustments to bring the mires into equal circumference can be done _________.
Back the tip off the eye slightly/on the eye.
Adjusting tonometry (Slit lamp)
Back tip off patient eye slightly, set beam intensity to widest point
PACG (primary angle closure glaucoma)
Can fully develop in 30-60 min, Halos, Women more often affected. Extremely high IOP 50-60 mmHg, Total blockage of drainage system.
Pulsation of mires
Caused by venous pulse in the eye. Always record if you see pulsing.
Goldman calibration check
Check the calibration of the slit lamp mounted Goldman tonometer with the calibration rod of measured weights at 0, 2, and 6g corresponding 0, 20, and 60 mmHg
How aqueous is produced
Ciliary process
tonometry instrument
Cobalt blue filter, low magnification, light beam all the way tall and all the way wide, and light intensity bright
Other factors that can affect IOP during tonometry
Corneal thickness, highest stigmatism, time last glaucoma drops were instilled.
Tonopen disadvantages
Disadvantage is: accuracy is questioned by Some, factory calibration, expensive to buy, operate and repair. Displaces significant aqueous, Latex allergy- some tips contain latex.
Advantages of applanation tonometry
Does not need frequent calibration, easy to clean and sanitize, scleral rigidity not a factor due to very little aqueous displacement, IOP directly related to dial, more accurate readings within plus or -0.5 mmHg.
Tonometry
Done on every patient, measures IOP, can detect undiagnosed glaucoma
Glaucoma "suspect"
Elevated IOP, no damage, no optic nerve cupping or visual field defect
Goldmann tonometer
Equal size and inner Mire edges touching
Temporary causes of decreased IOP
Exercise, large decrease in blood pressure, general and retro bulbar anesthesia, intraocular surgery, retinal or choroidal detachment, inflammation, accommodation, muscle relaxants
(The thicker the cornea the more easily it is in dented. If the cornea is relatively thin The actual intraocular pressure is lower than the measure value and vice versa.) True or false?
False, accuracy of IOP is affected by corneal thickness. The thinner the cornea, the more easily it is indented. If the corneal thickness is relatively thin, the actual IOP is higher than the measured value.
If the patient's corneal astigmatism is LOWER than 3 dpt, rotate the tonometer Prism Until the red marking on the prism holder is aligned with the axis mark that corresponds to the patients minus cylinder axis. True or false?
False, if the patients Corneal astigmatism EXCEEDS 3D Then rotate the tonometer Prism until the red marking on the prism holder is aligned with the access mark that corresponds to the patients minus cylinder axis.
Factors that can affect IOP during tonometry
Falsely elevated from: tight collar or neck tie, squeezing eyelids, breath holding, incorrectly performed alignment, improper amount of fluoroscein, Falsely low from: repeated IOP measurements, incorrectly performed tonometry/alignment, improper amount of fluoroscein.
Causes of Hypotony
Flat anterior chamber, wound leak, OVERFILTRATION, Choroidal detachment, Retinal detachment
What is the diurnal curve?
Fluctuation is normal IOP of 3 to 5 mm within a 24 hour period, being highest at 6 AM.
POAG (primary open-angle glaucoma)
Gradual Blockage of drainage channel, gradual loss of side vision, IOP builds slowly
Astigmatism
Greater than 3 diopters of cylinder power, not symmetrical, use the minus cylinder axis on red line of probe tip
Describe the alignment corneal mires when IOP is accurate?
Half circles of equal circumference above and below horizontal midline and inner edges touching
It takes more force to flatten a ***** than a ******cornea
Hard, soft
Function of Aqueous
Helps sustain normal eye pressure
Hard cornea
High IOP
False reading on Goldmann
Holding breath, tight collar, pressure on globe while holding lids.
laymen explanation for tonometry test
I am going to check the amount of fluid pressure in your eye.
Hypotonic eye
IOP below 6 mmHG
diurnal curve
IOP changes throughout the day
IOP Diurnal curve is highest :
In the morning
IOP above 21
Increased suspicions for glaucoma
Shiotz tonometry
Indentation, not as accurate as other forms, only anesthetic without stain, tear film of miniscus is insignificant.
Indentation tonometry
Influenced by scleral rigidity and repeated readings can result in increased aqueous outflow and raise IOP
iCare tonometer
Instrument to check IOP 1.8 mm diameter plastic ball on a stainless steel wire is held in place by an electromagnetic field and a handheld battery power device. No gtts needed.
when mires are not touching
Interocular pressure reading is too low. To correct turn the dial slowly away from you to bring the inner edges to touch.
Soft Cornea
Low IOP
What type of glaucoma can cause optic nerve damage with low IOP and what causes this?
Low tension glaucoma, it is believed to be due to poor posterior ciliary circulation
If there is a greater than 3 dpt of corneal a stigmatism, the........................ can be set at the red line on the Prism holder.
Minus cyl axis
Air-puff tonometry (NCT)
Non-contact to indent the eye, no drops, no risk of abrasion, no blurred vision, NOT as accurate
What are two diagnosis when IOP is high and no optic nerve damage?
Ocular hypertension and glaucoma suspect
tonometry procedure
Ocular magnification set at left/lowest, Force adjustment set at 10 mmHg, High power light
Bi-prism rule
Over 3 diopter of + cylinder requires the minus cylinder axis to be on the red line. Ex +1.00 + 4.00 ×43. Set Bi-prism at 133 on red line. 43 in plus cylinder = 133 in minus cylinder
Which is not a test/instrument to measure IOP specifically? Pachymetry, Perkins tonometer, Tonopen, pneumatonomometer
Pachymetry
Reasons to perform tonometry
Part of a complete exam, suspect iritis or angle closure glaucoma, hyphema, hypopyon, or sub conjunctival hemorrhage seen, Patient was hit in the eye and now I feel sick to stomach, within one hour after YAG laser or after cataract surgery.
How would you accurately measure IOP if patient has greater than 3 dpt of astigmatism?
Perform keratometry and describe the amount of corneal astigmatism and axis of the flattest K and set that access on the tonometer 43° Redmark.
tactile tonometry
Perform on children under 12 and press on your own eye to compare
Biggest advantage to Perkins tonometer and tonopen
Portability
Goldmann Applanation
STANDARD. Considered most accurate form of tonometry, applanation type, 3.06 mm contact with cornea, no significant increase in IOP, measures force to flatten corneal surface, requires more training to perform
Recording tonometry
Schiotz Tonometry= Ts Goldmann Applanation= TA Tactile Tension= Tt * always record the time the test was taken and time when drops were installed
What to look for prior to applanation Tonometry
Seidel positive or negative Foreign body
Disadvantages of applanation tonometry
Slit lamp Goldman lacks portability, unreliable measurements from corneal scars or high astigmatism, more expensive, patient needs anesthetic and fluorescein, risk of abrading cornea, the eye must be anesthetized, technique requires more training.
Temporary causes of elevated IOP
Steroid responders, large increase in blood pressure, restricted EOMs, cycloplegic drugs
False low on Goldmann
TOO LITTLE flourescein
False high on Goldmannn
TOO MUCH flourescein
Intraocular pressure is produced mainly by
The balance between the production and flow of aqueous fluid in the ease of which it leaves the eye
tonometry
The measurement of the eye's pressure, better known as intraocular pressure, and is measured in the unit millimeters of mercury (mmHg)
scleral rigidity
The resistance to stretching of the eye to changes in shape with changes in intraocular pressure.
In applanation tonometry the higher the IOP:
The smaller the flattened area will be
If the mires are too wide (thick) is the IOP going to be artificially higher or lower? How about if mires are too narrow (thin)?
Thick: Overestimation Thin: Underestimation
Pachymetry
Thickness of the cornea
Pneumotonometer
This modality of IOP measurement measures 7 pulses and selects the best 5 to calculate (A lot of doctors like to use this if patient has high astigmatism and otherwise normal.)
Why is it important to record the time tonometry was done?
Time glaucoma drops were last used is recorded and if you check IOP one hour after drop application it most likely will differ then if you check it 11 hours after drop application for drops Wear off
Thick cornea
Tip WILL NOT applanate causing false high IOP
Thin cornea
Tip WILL applanate causing false low IOP
tonometry test
To measure the interocular fluid pressure within the eye in millimeters of mercury greater than that of the atmospheric pressure
It may be necessary to hold a patient's lids for tonometry. When holding a patient's upper lid, the patient's upper lid should be held firmly against the patients orbital rim to avoid pressing against the globe. True or false?
True
To increase pressure reading:
Turn the dial away from you, towards the patient
To decrease the pressure dial reading:
Turn the dial towards you, away from the patient.
How would you accurately measure IOP if patient were one day postop trabeculectomy or any surgical filtering procedure?
Turn the millimeters of mercury dial to zero and very gently applanate the cornea pressing no further than necessary to see the corneal mires come in to view, Then back away and likely increase mmHg and repeat with this ONE TOUCH METHOD.
Indentation versus applanation
Two methods of tonometry
Seidel test
Used to determine ruptured globe (positive test = leaking of aqueous through fluroscein stain - fluroscein in tear drop pattern)
open angle glaucoma
What is the most common type of glaucoma that causes moderately elevated IOP?
Factors that can affect intraocular pressure
What time of day, breathing, pulse of central retinal artery, diurnal curve
Glaucoma
a group of eye diseases characterized by increased intraocular pressure
Schiotz tonometer
an example of an applanation tonometer, In frequently used. (Advantages are it is small and portable and can be used in an OR. Disadvantages are it must be disassembled and cleaned after use, risk of abrading cornea and must use a chart to convert.)
Seidel test
an eye test used to assess the presence of anterior chamber leakage in the cornea
aqueous flow
anterior chamber angle -> trabecular meshwork -> canal of Schlemm -> aqueous vein
Hyphema
blood in the anterior chamber of the eye
subconjunctival hemorrhage
blood in the white part of the eye
ciliary processes
contain capillaries that secrete aqueous humor
Tactile tension
finger pressure is exerted on the eye to determine if the eye is hard or soft, indicating a high or low pressure. It is recorded as soft or hard.
Tonopen (tonometer)
instrument used to measure intraocular pressure
indentation tonometry
measures the amount of indentation produced by a fixed weight (Shiotz) To flatten a small area of the cornea. Not frequently used.
air-puff tonometry
non contact tonometer Uses a puff of air to flatten the cornea for IOP measurement
Glaucoma risk factors
older than 65 y/o, family history, African American decent, diabetes, myopia, ocular hypertension.
Glaucoma patients lose;
peripheral vision and is treated with meds
Hypopyon
pus in the anterior chamber
Disinfecting Goldmann tip
soaking .3% hydrogen peroxide or 1:10 dilution of liquid bleach solution
Seidel sign
stream of stained yellow vitreous fluid
anterior chamber of eye
the space between the cornea and the iris, filled with aqueous humor
hypotony means
very low IOP (collapsing globe like over filtering bleb), 6 mmHg or below.
Goldmann tonometry:set up
•Adjust the patient for comfort, able to breathe normally, chin is on the chin rest and forehead is on the fore head band. •Bright light source off temporally to the same side of the eye you're checking •center the prism over the cornea •Look for the ghost mires to be centered
Equipment disinfection and maintenance
•Reusable tips should be disinfected between patients •The applanation tonometer can be cleaned with alcohol •Soak the prism tip for 10 minutes and either 3% hydrogen peroxide or 1 to 10 liquid bleach solution then rinse thoroughly and dry
Glaucoma Work-up include:
•Va •IOP •Pupils •VF •Pachymetry •Gonioscopy •OCT •Stereo ON photos
