Tonometry CH17

Question 1

When cleaning the applanation tonometer, one must be careful not to:
a) remove the biprism
b) bend the pressure-sensitive arm
c) turn the adjustment knob
d) cause scleral rigidity

Answer 1

b) The moveable arm that holds the biprism can be bent if care is not taken.

Question 2

The applanation tonometer unit itself may be cleaned by:
a) immersing in 3% hydrogen peroxide
b) spraying and wiping with electronics cleaner
c) gently wiping with damp cloth and mild soap
d) spraying with disinfectant

Answer 2

c) This recommendation comes from the manufacturer.6 It is never a good idea to spray cleaner directly onto an instrument.

Question 3

The tonometer tip should be cleaned:
a) prior to being sterilized
b) prior to being autoclaved
c) prior to being boiled
d) prior to being disinfected

Answer 3

d) Technically, cleaning removes soil and debris and some germs. Disinfecting is the
removal of all or most germs except bacterial spores (which are killed by sterilization).
External debris is removed first (or at the same time) in order to allow all instrument surfaces to come into contact with the disinfectant.

Question 4

The tonometer tip should be disinfected:
a) morning and night
b) first thing each day
c) every 10 minutes
d) between each patient

Answer 4

d) Because the tonometer tip contacts the cornea and tear film, it must be disinfected (or a fresh, disinfected tip inserted) between each patient.

Question 5

To best disinfect the tonometer tip, one should:
a) wipe it with a moist tissue
b) swipe it with an alcohol wipe
c) put it in a 10-minute soak in 3% hydrogen peroxide
d) place it in the autoclave for 15 minutes

Answer 5

c) A 10-minute soak of bleach (1:10 dilution) or hydrogen peroxide is the best disinfection
method. A moist tissue will not disinfect, nor will a quick “swipe” with alcohol (although
some references suggest a 10-second wipe as acceptable). The autoclave will melt the
tonometer tip.

Question 6

With regular use, soaking the tonometer tip in alcohol:
a) will not affect it
b) will cause the numbers to fade
c) will cause etching on the face
d) will cause the plastic to soften

Answer 6

b) Repeated exposure to alcohol can cause the numbers and lines on the side of the tonometer tip to fade and disappear.

Question 7

Failure to properly rinse the tonometer tip after disinfecting and prior to using it
could result in:
a) corneal chemical burn
b) inaccurate readings
c) etching of the tip’s surface
d) clouding of the mires

Answer 7

a) Alcohol and hydrogen peroxide can cause marked discomfort, so the tip should be rinsed well and dried before using.

Question 8

Check calibration on the Goldmann applanation tonometer by:
a) placing the tip on a test block
b) measuring an eye of known pressure
c) use of a calibration bar
d) returning it to the manufacturer

Answer 8

c) A calibration bar is placed in a special attachable holder when calibrating an applanation tonometer. If the calibration is not accurate, the instrument must be returned to the manufacturer.

Question 9

When calibrating the Goldmann applanation tonometer at the 2 setting, the tonome-
ter head should move:
a) no more than ±0.50 from the tested position
b) 1.0 from the tested position
c) freely in every position
d) not at all

Answer 9

a) Movement of the tonometer arm should occur within 0.50 of the drum setting of 2. If
you must turn the drum more than 0.50 before the arm will move, this indicates that the instrument is not accurate. Thus, when you are calibrating at 2, the arm should “rock”
between the 1.95 and 2.05 reading on the drum.7,8

Question 10

The test positions for calibration of the Goldmann applanation tonometer are:
a) 0, 22, and 45 mm Hg
b) 0, 20, and 60 mm Hg
c) 10, 20, and 50 mm Hg
d) 0, using a test block

Answer 10

b) The calibration bar is marked to check the 0, 20, and 60 mm Hg readings on the tonometer. Especially pay attention to the calibration at 20 mm Hg, as this is often the crucial point in patients with glaucoma.

Question 11

If you are calibrating an applanation tonometer for the 20 mm Hg setting, the drum
will read:
a) 1
b) 2
c) 4
d) 5

Answer 11

b) Remember, the drum readings are multiplied by 10, so the 20 mm Hg reading would translate to “2” on the drum.

Question 12

If the applanation tonometer falls outside of the calibration allowance:
a) add or subtract from the final reading to offset the problem
b) bend the tonometer arm until calibration is accurate
c) turn the screw in the tonometer arm until calibration is accurate
d) return the tonometer to the manufacturer for calibration

Answer 12

d) Answers a through c might sound good, but the only way to recalibrate the tonometer is to return it to the manufacturer for servicing.

Question 13

The applanation tonometer measures intraocular pressure (IOP) by:
a) measuring the amount of pressure needed to indent the cornea
b) measuring the amount of time needed to flatten the cornea
c) measuring the IOP directly
d) measuring the amount of pressure needed to flatten the cornea

Answer 13

d) The applanation tonometer flattens the cornea and measures the amount of pressure
required to do so. (By contrast, indentation tonometry measures the amount of pressure
required to indent the cornea.)

Question 14

IOP as measured by applanation is recorded as:
a) mm Hg
b) gm/mm2
c) a scale from 0 to 18
d) lb/in2

Answer 14

a) Applanation tension is measured in millimeters of mercury (mm Hg).

Question 15

Once the cornea is applanated, the force of the applanation tonometer is increased or
decreased:
a) until the outer edges of the mires touch
b) until the edges of the mires overlap
c) until the inner edges of the mires touch
d) until the upper mire is larger

Answer 15

c) The inner edges of the mires should touch when the reading is taken.

Question 16

Wide mires in applanation tonometry will result in:
a) accurate readings
b) falsely low readings
c) falsely high readings
d) increased patient comfort

Answer 16

c) Wide mires (too much fluid) result in falsely high readings.

Question 17

Thin mires in applanation tonometry will result in:
a) accurate readings
b) falsely low readings
c) falsely high readings
d) decreased patient comfort

Answer 17

b) Thin mires (not enough fluid) result in falsely low readings.

Question 18

All of the following can cause applanation tonometry errors except:
a) too much or too little fluorescein
b) lack of contact with the eyelid
c) misalignment of mires
d) dirty tonometer face

Answer 18

b) The tonometer should not contact the eyelid at all.

Question 19

All of the following can result in inaccurate applanation readings, with no compensa-
tion method available, except:

a) astigmatism
b) pterygium
c) corneal scars
d) corneal graft

Answer 19

a) Astigmatism over 3 D must be compensated for (see answers 36-38). There is no way to set the tonometer to compensate for a pterygium, scar, or graft—all of which can cause an
inaccurate reading.

Question 20

The applanation tonometer is preferred in cases of low scleral rigidity because:
a) it does not displace an appreciable amount of aqueous and, therefore, does not cause
distention of the ocular structures
b) it does not flatten the cornea and, therefore, does not cause distention of the ocular structures
c) it is performed with the patient in a seated position and, therefore, gravity can equalize
distention of the ocular structures
d) topical anesthetic is used and, therefore, does not cause distention of the ocular structures

Answer 20

a) The applanation tonometer does not displace a significant enough amount of aqueous to cause even a more pliable eye to distend.

Question 21

The biprism design of the applanation tonometer:
a) makes it easier to align than an indentation tonometer
b) makes it more accurate than indentation tonometry
c) offsets scleral rigidity factors
d) makes it more comfortable than indentation tonometry

Answer 21

a) With the biprism, you have visual proof (the mires) of correct alignment.

Question 22

Each of the following is an advantage of applanation tonometry except:
a) it gives an excellent binocular view of the mires
b) it is the most accurate method of checking IOP
c) the tonometer tip is easily cleaned and disinfected
d) it is accurate even in the presence of low scleral rigidity

Answer 22

a) The mires appear in only one ocular, making it monocular, not binocular. The other statements are true.

Question 23

Disadvantages of applanation tonometry include all of the following except:
a) it is expensive
b) slit-lamp models are not portable
c) it can be difficult to learn to use
d) one must use a chart to convert the reading

Answer 23

d) You do not need a conversion chart with applanation tonometry. The measurement is read directly off the drum.

Question 24

Match the following with the drawings using each answer only once. (All drawings
reprinted with permission of Herrin MP. Ophthalmic Examination and Basic Skills.
Thorofare, NJ: SLACK Incorporated; 1990.)

proper position for measurement,
too close, reading is too low,
too far back, reading is too high
too much fluorescein,
vertical position is off,
not enough fluorescein

Answer 24

C) proper position for measurement
A) reading is too low
H) reading is too high
E) vertical position is off
D) too close
G) too far back
F) too much fluorescein
B) not enough fluorescein

Question 25

You have just realized that you instilled regular fluorescein into an eye with a soft
contact. What do you do next?
a) perform the applanation over the lens
b) remove the lens, and rinse it immediately
c) irrigate the eye with the lens in it
d) slide the lens to the side, and take the measurement

Answer 25

b) If you remove the lens and rinse it right away, you may be able to get the dye out before the lens is too stained.

Question 26

For proper applanation, the slit-lamp light should be set up as follows:
a) at a 60 degree angle, with the cobalt blue filter, and with the light source completely
open
b) at a 45 degree angle, with the red-free filter, and with the light source completely open
c) at a 90 degree angle, with the cobalt blue filter, and a narrow beam
d) at a 60 degree angle, with the cobalt blue filter, and a pinpoint light beam

Answer 26

a) To perform applanation tonometry, the light source should be at a 60 degree angle with the cobalt blue filter and full illumination.

Question 27

During applanation tonometry, the patient is instructed to:
a) close the eye not being tested, hold his or her breath, and look up
b) open both eyes, breathe normally, and look to the right
c) open both eyes, breathe normally, and look straight ahead
d) open both eyes, hold his or her breath, and look straight ahead

Answer 27

c) Applanation tensions are easier if the patient will open both eyes. The patient must look straight ahead for proper alignment. The patient should not hold his or her breath, as this can cause a falsely elevated IOP reading.

Question 28

Each of the following can be key in accurate applanation tonometry except:
a) the patient should loosen a tight collar
b) the patient should clamp his or her teeth
c) the patient should not strain to reach the slit lamp
d) the patient should relax the shoulders and neck

Answer 28

b) The reading will be most accurate if the patient is relaxed.

Question 29

Your patient is a 45-year-old executive. You have just taken his applanation tonometry
reading, and it is 28. There is no history of glaucoma in the family. His readings for
the past 10 years at annual exams in your office have been 20. You lean back, scratch
your head, then ask the patient to:

a) come back for a reading in the afternoon
b) drink a lot of water to see if this will affect the pressure reading
c) loosen his tie and collar, then repeat the measurement
d) let you recheck with the Schiøtz tonometer

Answer 29

c) Have him loosen his tie and collar and try again. (The physician would be the one to
order answers a or b.) The Schiøtz is less accurate than the applanation tonometer.

Question 30

If, during applanation tonometry, it is noticed that the mires are not aligned, the
proper procedure is to:
a) adjust the joystick to realign
b) adjust the pressure reading accordingly
c) adjust the pressure reading using the appropriate chart
d) back off the eye, adjust the joystick, then reapplanate

Answer 30

d) Pull the tonometer off the cornea just slightly before adjusting position. Do not slide the tip around on the cornea.

Question 31

Each mark on the applanation tonometer drum stands for:
a) 10 mm Hg
b) 2 mm Hg
c) 1 mm Hg
d) 2 g/mm2

Answer 31

b) Each mark on the tonometer drum represents 2 mm Hg.

Question 31

Between measuring the two eyes, it is helpful to ask the patient to:
a) look left then right to help him or her relax
b) blink to redistribute the fluorescein
c) blot his or her eyes with a tissue
d) look straight ahead without blinking

Answer 31

b) We ask the patient not to blink during the test, so the second eye may tend to be a little
dry. A quick blink will spread the dye across the cornea.

Question 32

The reading on the applanation tonometer drum is 2. The patient’s IOP is:
a) 20 mm Hg
b) 4 mm Hg
c) 2 mm Hg
d) 4 g/mm2

Answer 32

a) If the number 2 on the drum is on the marker line, the IOP is 20. Each mark is 2 mm Hg, but each number is 10 mm Hg.

Question 33

In properly aligned applanation tonometry:

a) there are no factors that affect the IOP
b) the mires will pulsate slightly with the heartbeat
c) the mires will pulsate slightly when the patient breathes
d) accuracy is ensured if the patient does not blink

Answer 33

b) The mires may pulsate slightly with the heartbeat (not with breathing). Even with accurate alignment, however, there are other factors that can induce error.

Question 34

When the applanation tonometer mires pulsate, the IOP:
a) is the lowest of the readings
b) is the highest of the readings
c) is the difference between the 2 readings
d) is at the midpoint between the 2 readings

Answer 34

d) Take the reading at midpoint between the readings during the pulsations.

Question 35

One must make an adjustment to the applanation tonoprism if the patient’s corneal
astigmatism is:
a) greater than 1 D
b) greater than 2 D
c) greater than 3 D
d) greater than 4 D

Answer 35

c) The “magic number” is 3 D when it comes to resetting the tonoprism for astigmatism.
Failure to do so may result in an erroneous measurement (see answers 37 and 38 for more information).

Question 36

If compensation for high corneal astigmatism is not made to the applanation tonom-
eter, the IOP measurement could be in error by:
a) 1 mm Hg
b) 2 to 3 mm Hg
c) 4 to 5 mm Hg
d) 8 to 10 mm Hg

Answer 36

b) If the biprism is not adjusted properly for the astigmatic cornea (more than 3 D), the IOP measurement could be 2 to 3 mm Hg off.

Question 37

In order to compensate for high astigmatism with the applanation tonometer, the
biprism should be aligned as follows:
a) the steepest axis aligned with the red line on the holder
b) the plus axis aligned with the red line on the holder
c) 45 degrees from the minus cylinder should be placed in the 90-degree position
d) the minus axis aligned with the red line on the holder

Answer 37

d) Turn the biprism so that the axis (in minus cylinder) is in line with the red mark on the
tonometer holder. It is best to get the cylinder reading from the keratometer rather than the
patient’s glasses prescription, because the glasses may also correct for lenticular astigmatism. (Note: Some sources say to turn the biprism 45 degrees from the flattest axis, which is the point indicated by the red line on the holder.)

Question 38

A scarred, irregular cornea is difficult to measure with the applanation tonometer
because:
a) there is decreased scleral rigidity
b) one cannot instill topical anesthetic because of tissue melt
c) one cannot use fluorescein because it will infiltrate the tissue
d) the mires are irregular, making it difficult to judge the endpoint

Answer 38

d) If the cornea is irregular, the mires will also be irregular. This makes it tough to tell when
the inner edges are meeting.

Question 39

The most common complication of contact tonometry is:
a) fainting
b) allergy to anesthetic drops
c) cardiac arrest
d) conjunctivitis

Answer 39

d) Spreading conjunctivitis from one patient to the next is the most common complication
of contact tonometry.

Question 40

Corneal abrasions from tonometry can best be reduced by:
a) use of anesthetic
b) proper fixation
c) proper lighting
d) holding the lids securely

Answer 40

b) If the patient will fixate properly, holding the eye still, the risk of corneal abrasion is
minimized. (Holding the lids securely would help, but b is the best answer.)

Question 41

Measuring IOP is contraindicated in any patient:
a) who is nervous about the procedure
b) who has possible optic nerve disease
c) who has vision below 20/200
d) who might have a penetrating injury

Answer 41

d) A patient with a penetrating injury has an opening for bacteria to be introduced into the
eye via fingers, eye drops, tonometer tip, etc. In addition, aqueous could be forced out of
the eye during applanation.

Question 42

Any type of contact tonometry must be avoided, if possible, in which patient?
a) patient with acquired immune deficiency syndrome (AIDS)
b) patient with a corneal graft
c) patient with epidemic keratoconjunctivitis
d) children younger than 8 years of age

Answer 42

c) Epidemic keratoconjunctivitis is extremely contagious! There is no contraindication in
any of the other cases.

Question 43

If the patient has known human immunodeficiency virus (HIV), the assistant should:
a) refuse to take a pressure on the patient
b) use only the noncontact tonometer
c) wear gloves during contact tonometry
d) place a tissue on the tonometer prism

Answer 43

c) HIV has been isolated from human tears, so gloving is a wise precaution. (However, to
my knowledge, there have been no reports of the virus being spread through contact with
tears.)

Question 44

A patient who reports an allergy to topical anesthetics:
a) should have his or her IOP checked with a noncontact tonometer
b) should be irrigated after contact tonometry if topical anesthetic is used
c) cannot have a pressure check of any kind
d) should tough out contact tonometry without drops

Answer 44

a) Use the noncontact tonometer on the patient who is sensitive to topical anesthetic, and you cannot go wrong. Answer b could be done if your doctor orders it. (The words “can-
not…of any kind” should have clued you in that answer c was wrong.) I have done an
occasional applanation tension using tear drops only, but it is not ideal.

Question 45

All of the following can result in a falsely high IOP reading except:
a) breath holding
b) moving the eye during the measurement
c) straining to lean into the slit lamp
d) squeezing the eyelids

Answer 45

b) Moving the eye during measurement changes alignment but does not falsely elevate the reading.

Question 46

Schiøtz tonometry measures IOP by:
a) measuring the force it takes to equalize the eye’s internal pressure
b) measuring the force exerted on the instrument by the eye
c) measuring the force it takes to flatten an area of the cornea
d) measuring the force it takes to indent the cornea

Answer 46

d) Schiøtz tonometry measures IOP by indentation.

Question 47

The Schiøtz tonometer readings:
a) are read from the instrument in millimeters of mercury
b) are read from the instrument in gram weights
c) must be converted to millimeters of fluorescein by use of a calculator
d) must be converted to millimeters of mercury by use of a chart

Answer 47

d) The Schiøtz reading must be converted to mm Hg by use of a graph or chart.

Question 48

The Schiøtz tonometer should be disinfected:
a) at the beginning of each day
b) at the end of each day
c) between each patient
d) when it appears dirty

Answer 48

c) Because the Schiøtz comes in direct contact with the cornea and tear film, it must be
disinfected between each patient.

Question 49

Patient position for Schiøtz tonometry is:
a) sitting up to the slit lamp
b) sitting up in the exam chair
c) lying back in the exam chair
d) sitting at a 45 degree angle

Answer 49

c) The patient must lie flat on his or her back for the reading.

Question 50

The patient is apprehensive about having that “air puff” test. She is most likely refer-
ring to:
a) the TonoPen
b) the corneal sensitivity test
c) a corneal biopsy
d) noncontact tonometry

Answer 50

d) Noncontact tonometry is often called the “air puff” test.

Question 51

The noncontact, or “air puff,” tonometer measures:
a) the IOP directly
b) either the time or force required to indent the cornea
c) either the time or force required to flatten the cornea
d) either the time or force required to photograph the cornea

Answer 51

c) The noncontact tonometer may measure either time or force required to flatten the cornea.

Question 52

The noncontact tonometer is most useful for:
a) monitoring patients with glaucoma
b) differentiating between ocular hypertension and glaucoma
c) finding patients with low-tension glaucoma
d) screening situations

Answer 52

d) The noncontact tonometer is adequate for screening, but will miss some elevated pres-
sures. Thus, it is not sensitive enough for monitoring or diagnosing glaucoma.

Question 53

The aqueous humor is produced by the:
a) ciliary muscle
b) ciliary body
c) trabecular meshwork
d) iris

Answer 53

b) The ciliary body, at the base of the iris (but not the iris itself), is responsible for aqueous
production.

Question 54

The composition of the aqueous is most like:
a) blood plasma
b) tears
c) saliva
d) mucus

Answer 54

a) Blood plasma is most like aqueous in composition, with some difference in trace elements.

Question 55

The flow of aqueous in the eye follows this pattern:
a) angle, posterior chamber, pupil, anterior chamber
b) angle, anterior chamber, pupil, posterior chamber
c) pupil, posterior chamber, anterior chamber, angle
d) posterior chamber, pupil, anterior chamber, angle

Answer 55

d) The aqueous flows out of the posterior chamber, through the pupil, into the anterior
chamber, and then through the angle.

Question 56

As it exits the eye, aqueous humor flows in this pattern:
a) canal of Schlemm, trabecular meshwork, episcleral arteries
b) trabecular meshwork, canal of Schlemm, episcleral veins
c) trabecular meshwork, nasolacrimal duct, episcleral arteries
d) canal of Schlemm, episcleral veins, trabecular meshwork

Answer 56

b) The flow of aqueous humor exiting the angle goes through the trabecular meshwork, into the canal of Schlemm, and from there into the episcleral veins. (Remember that veins carry blood to the heart. Arteries bring blood to an organ.)

Question 57

IOP is determined by:
a) systolic and diastolic blood pressure
b) rate of aqueous production and resistance to outflow
c) pressure in the ophthalmic artery and vein
d) cranial pressure transferred to the eye through the optic nerve

Answer 57

b) IOP results from the combination of the amount of aqueous produced over time and its ability to drain out of the eye.

Question 58

Reduction and control of elevated IOP is based on:
a) lowering the diastolic and systolic blood pressure
b) lowering cranial pressure
c) increasing aqueous production and/or decreasing outflow
d) decreasing aqueous production and/or increasing outflow

Answer 58

d) In order to lower the IOP (theoretically, at least), decrease the amount of aqueous being
produced and/or increase the draining of it.

Question 59

Which of the following regarding aqueous and IOP is not true?
a) IOP is generally higher in the morning than in the evening.
b) IOP is slightly higher in the posterior chamber than in the anterior chamber.
c) Aqueous has no effect on the optical system of the eye.
d) Aqueous provides nutrition and waste removal for internal ocular structures.

Answer 59

c) While slight, the aqueous does exert a refractive influence on light entering the eye. The IOP is slightly higher in the posterior chamber because the aqueous meets some resistance as it encounters the margin of the pupil. The circulating aqueous also acts to bring nutrients to and remove wastes from the eye’s internal structures. Regarding answer a, see answer 61.

ANSWER 61: IOP varies during the day (“diurnal”). It is usually higher early in the morning and lower during the afternoon. (In monitoring glaucoma, many physicians will vary the time of day that a patient comes in for IOP checks, to get a clearer idea of how treatment is affecting the pressure.)

Question 60

Regarding the normal diurnal variation of IOP:
a) IOP is higher early in the morning
b) IOP is lower early in the morning
c) IOP reaches a peak around noon
d) IOP is lowest around noon

Answer 60

a) IOP varies during the day (“diurnal”). It is usually higher early in the morning and lower
during the afternoon. (In monitoring glaucoma, many physicians will vary the time of day that a patient comes in for IOP checks, to get a clearer idea of how treatment is affecting the pressure.)

Question 61

The diurnal curve of IOP in a glaucoma patient:
a) may vary by 4 mm Hg
b) may vary up to 10 mm Hg
c) is less than in an eye without glaucoma
d) shows no variation in morning versus evening

Answer 61

b) The diurnal curve of the IOP in a patient with glaucoma may vary up to 10 mm Hg, being higher in the morning. The average (nonglaucomatous) eye varies only by about 4 mm Hg. Thus, this larger fluctuation is a factor in both diagnosis and treatment of glaucoma.

Question 62

Elevated IOP as seen in chronic open-angle glaucoma is believed to be the result of:
a) decreased function of cells in the trabecular meshwork
b) obstruction of the trabecular meshwork by particles
c) overproduction of aqueous
d) optic nerve damage

Answer 62

a) The degeneration of the trabecular meshwork (in function and/or cell density) as seen in open-angle glaucoma is not a product of the normal aging process. It seems to be disease-specific. Obstruction by particulate matter would be a secondary glaucoma. While over-production of aqueous does exist, it is not the primary entity in open-angle glaucoma.

Question 63

Patients who experience an increase in IOP while using corticosteroids are called:
a) ocular hypertensives
b) glaucoma suspects
c) steroid regulators
d) steroid responders

Answer 63

d) Steroids do not cause a rise in IOP in every patient, but those patients who do experience an IOP increase while on steroids are known as steroid responders.

Question 64

If the cornea is extremely thick or scarred:
a) the IOP measurements will always be underestimated
b) the IOP measurements will always be overestimated
c) the IOP measurements can be accepted with reservations
d) no tonometric measurement will be accurate enough to satisfy clinical needs

Answer 64

d) This opinion comes from Brubaker in his excellent article entitled Tonometry.
10 Other sources agree.

Question 65

You are about to do applanation tonometry on a patient, and she asks, “Will this tell
you if I have glaucoma?” You answer:
a) “Yes, but Dr. Jackson will give you the results.”
b) “Only if the reading is abnormal.”
c) “No, this is just a screening.”
d) “Eye pressure is just one part of diagnosing glaucoma.”

Answer 65

d) Although often called “the glaucoma test,” tonometry by itself is not adequate to diagnose glaucoma.