Tonometry 1 Flashcards by m f

Circulation of aqueous delivers ___ to and removes ____ from ____.

Delivers oxygen and nutrients and removes waste from posterior cornea, lens and anterior vitreous (avascular structures)

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Hypotony

Very low IOP <5mmHg

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Very low IOP could be due to

Post surgery wound leaks

CB disease

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Low IOP can lead to (hypotony)

Corneal decompensation, macular edema, choroidal effusions, etc

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Acute elevation of IOP can be due to

Acute decline in aqueous outflow

Angle closure, inflammation, neovascularization

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Acute elevation of IOP can lead to

Insufficient perfusion of ONH and subsequent optic atrophy (ischemic optic neuropathy)

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Chronic elevation of IOP is

Slow gradual rise of IOP, compensatory mechanisms have time to operate avoiding the symptoms of acute IOP elevation

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Chronic IOP elevation is almost always a consequence of

Decreased aqueous outflow facility

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Chronic elevation of IOP is usually idiopathic but may also occur secondary to

Pigment deposition, exfoliation syndrome, etc

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During chronic elevation of IOP ___ arises in susceptible individuals

Optic neuropathy

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IOP is important in an eye exam because of

Screen for glaucoma 
Future comparison in glaucoma pts 
Detect wound leak in post op/trauma 
Rule out acute glaucoma 
Detect drug reactions for corticosteroids 
Monitor glaucoma therapy

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Any attempt of measuring IOP will often change it by

causing an artificial rise in pressure

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Gold standard of measuring IOP due to historical reasons

Goldman

Not because its less subjected to influences

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Measured IOP is influence by

Biochemical properties like corneal rigidity, thickness and hysteresis

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IOP is highly variable and its measurement is subject to

Considerable error

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IOP is dynamic meaning

It’s constantly changing and each reading is at best a snapshot of the IOP in that moment

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A change in about 3mmHg is considered

Clinically significant, smaller changes are likely to be noise or measurement error

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Time of day, cardiac cycle and body position can

Change IOP

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IOP is highest at what time of the day?

Early morning

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IOP is increased during what part of the cardiac cycle?

Systole

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IOP increases during what body position

When position is changed from upright to recumbent

head down position

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IOP changing during changing body positions is believed to be due to

Episcleral venous pressure

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The variability (difference) between IOPs in the same eye during different visits is ____ than the variability of IOP of R & L eyes in one visit

Greater

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What is monocular treatment trial

Since the correlations of IOP between eyes is so strong. One eyes may serve as a control when starting glaucoma medication

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What is a safe IOP

There is no IOP considered safe or unsafe

Target pressure is

A presumed safe IOP that is a certain amount less than IOP at glaucoma damage has occurred

A difference of more than 3mmH is considered ___ and is a risk factor for ___

Asymmetric | Glaucoma

Prevalence of asymmetry of IOPs between eyes _____ with age.

Increases

Each additional 1mmHg increase of IPA asymmetry between eyes is associated with _% increase of ____

21% of risk for development of glaucoma

Ocular pulse amplitude means _____. Which results from ___.

IOP increase during systole and decreases during diastole. Results from volume change in the blood entering the eye that occurs during systole

Normal ocular pulse amplitude is

3mmHg with <0.5 mmHg difference between eyes

Because of OPA, ____ is required to record and compensate for the pulse

Continuous Tonometry over several pulse cycles

During higher IOP, OPA usually

Increases

IOP will increase in __ position, largely due to elevation of ____

Supine | Elevation of episcleral venous pressure

IOP will increase ___ when changing from standing/ sitting straigh to supine position

2-4 mmHg

IOP will _____ when the body is upside down

Increase (2-3X)

Even though aqueous production decreases during night time, there is decreased outflow and increased episcleral venous pressure counteracting and causing

Overall increase in nocturnal IOP

Pressure is usually highest during __ and lowest in ___.

3-5 am | Lowest at 7-9 PM evening

The observed nocturnal rise in IOP is part of the reason why IOP is elevated during

IOP elevation while laying down

Diurnal IOP variation can still occur even in absence of

Postural effect

Diurnal IOP variation is due to various physiological reasons including

Ocular perfusion pressures, hormones, outflow facility during sleep

Large diurnal variation is suggestive of

Glaucoma

Normal diurnal amplitudes is

<5mm Hg

IOP measure in supine position will more closely approximate the nocturnal peak than

IOP measured in sitting position

Medication that ___ diurnal variation may be more effective in slowing down glaucoma

Dampen (decrease)

When measuring IOPs in glaucoma patients/ glaucoma treatment try to measure at the same time of the day

To minimize inter day variation

What is serial Tonometry

When IOPs are measured every 2hrs over a single 24hr period | Requires sleep lab or hospitalization

Water drinking test is used for

Evaluating diurnal variation in IOPs

Whats a positive/negative Water drinking test

An increase of 8-10 mmHg after rapid ingestion of a quart of water strongly suggests glaucoma. A negative test does not rule it out

Rapid ingestion of water causes fluid to move into the intraocular space, an abnormal outflow facility impairs its egress

Resulting in an increase in IOP

IOP undergoes rhythmic oscillations

Arterial pulse and respiratory cycle

BP effect on IOP

IOP is usually immune to small changes in BP Large swings in BP will cause transient shift in IOP in same direction

Elevation of EVP will

Raise IOP at a 1:1 ratio

Valsalva maneuver

Forced expiration against a closed glottis like coughing, chicking, vomiting, wind instruments, weightlifting

Valsalva maneuver can raise venous pressure and decreases arterial blood pressure which causes

Acute distinction of choroidal and orbital veins and increase in IOP of 10-20 mmHg

External pressure on eye effect on IOP

Initially it will raise IOP | After releasing, the pressure will be even lower than before the pressure was initially applied

Tomography effect

External pressure accelerates rate of aqueous outflow

What will happen if you repeat Tonometry a lot

Lower IOP

Forced eyelid closure affect on IOP

Increase iop 50 mmHg or more

Eyelid closure is a form of

External pressure

Normal blink

5-10mmHg transient rise in IOP

Voluntary fissure widening is a type of

External pressure About 2mmHg rise in IOP Can be avoided w careful lid retraction

In western countries IOP has a

Gradual upward trend with increasing age

In eastern countries

There will be a gradual downward trend of IOP with age

Regular excessive can affect IOP

Longer term lowering of IOP (about 4 mm Hg )

Hyper osmolarity affect on IOP

Rapidly draws fluid out of eye, lowering IOP (treatment of acute glaucoma)

Hypoosmolariy

Fluid enters the eye, raising IOP (water drinking test)

Systemic acidosis

Inhibit production of aqueous humor Carbonic a hydrate inhibitors

IOP does not define glaucoma but it is the only risk factor

Amenable to treatment

What IOP pressure should be considered suspect

>22mm Hg

Direct, intracameral pressure measurement of IOP

Manometry

Only method capable of recording the true intraocular pressure

Manometry

Simplest, least expensive, and least accurate method of measuring IOP

Digital palpitation

May be the only feasible method in patients unwilling or unable to undergo other forms of Tonometry

Digital palpitation

Transcorneal tonometry can be influenced can be influenced by

CCT and other corneal biochemical factors

Corneal biochemical factors may be affected by

Age, lasik and corneal disease ( keratoconus, Fuchs)

Greater CCT may lead to

Over estimation of IOP, degree of effect is variable (not a linear relationship)

General precautions of Tonometry

Poor patient cooperation, disinfect reusable probes, warn patients regarding air puff, irregular cornea and high astigmatism, caution with epithelial lesions and CL

gravity provides a known force on a weighted metal plunger. The lower the iop the farther into the cornea the plunger sinks and the higher scale reading

Schiotz Tonometry

The relative resistance an eye offers to expansion for a given rise in IOP is known as

Scleral rigidity

Does schiotz tonometry require anesthetia

Yes

Patient is supine, anesthetized, the Tono meter is lowered onto the core an until the full weight of the instrument is resting on the eye. Conversion chart is used to derive IOP

Schiotz Tonometry

The onset of the pressure of phosphene is

Correlated to IOP

Increasing pressure externally on the eye, a point of visual sensations is induced described as an eclipse of dark circle surrounded by a bright halo

Pressure phosphene Tonometry

Where is the phosphene Tonometer placed

Superonasal globe over the upper eyelid while the eye is looking inferno temporally

Does pressure phosphene tonometry require anesthetics

Provue(phosphene) tonometry is designed for

Home use

One of the newest forms of tonometry

Impact bound

Ballistic devices that measure the return bounce of an object after impacting the eye

Impact bound tonometry

Two types of impact rebound tonometry currently on the market

iCARE - transcorneal | Diatom- trans palpebral

iCARE can be used in

Upright and supine positions

Does iCARE require anesthetic

Sic reliable readings are obtained and the instrument will generate an average and discard unreliable readings

I care

Correlation between RBT and GAT

Good both equally affected by CCT

Tonometry that does not require a smooth regular cornea

I care

Can be performed over SCL

ICARE

Analyzes the declaration of a free falling metal rode after impacting the eyelid

Diaton Tonometry

Position used for diaton tonometry

Supine and eyes in downward gaze

Does diaton require anesthetics

Diaton is placed on

The upper lid margin

After 3 reliable reading the instrument calculates average

Diaton tonometry

Diaton relation with GAT

Poor agreement

Diaton relation with corneal biomechanics

Not affected because it is trans palpebral

Diaton has risks of false negatives because

It underestimates GAT at higher IOPs

Position for diaton

Supine or which fully extended neck

Tonometry 1 Flashcards

(105 cards)