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