Tonometry 1 Flashcards
Circulation of aqueous delivers ___ to and removes ____ from ____.
Delivers oxygen and nutrients and removes waste from posterior cornea, lens and anterior vitreous (avascular structures)
Hypotony
Very low IOP <5mmHg
Very low IOP could be due to
Post surgery wound leaks
CB disease
Low IOP can lead to (hypotony)
Corneal decompensation, macular edema, choroidal effusions, etc
Acute elevation of IOP can be due to
Acute decline in aqueous outflow
Angle closure, inflammation, neovascularization
Acute elevation of IOP can lead to
Insufficient perfusion of ONH and subsequent optic atrophy (ischemic optic neuropathy)
Chronic elevation of IOP is
Slow gradual rise of IOP, compensatory mechanisms have time to operate avoiding the symptoms of acute IOP elevation
Chronic IOP elevation is almost always a consequence of
Decreased aqueous outflow facility
Chronic elevation of IOP is usually idiopathic but may also occur secondary to
Pigment deposition, exfoliation syndrome, etc
During chronic elevation of IOP ___ arises in susceptible individuals
Optic neuropathy
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
Any attempt of measuring IOP will often change it by
causing an artificial rise in pressure
Gold standard of measuring IOP due to historical reasons
Goldman
Not because its less subjected to influences
Measured IOP is influence by
Biochemical properties like corneal rigidity, thickness and hysteresis
IOP is highly variable and its measurement is subject to
Considerable error
IOP is dynamic meaning
It’s constantly changing and each reading is at best a snapshot of the IOP in that moment
A change in about 3mmHg is considered
Clinically significant, smaller changes are likely to be noise or measurement error
Time of day, cardiac cycle and body position can
Change IOP
IOP is highest at what time of the day?
Early morning
IOP is increased during what part of the cardiac cycle?
Systole
IOP increases during what body position
When position is changed from upright to recumbent
head down position
IOP changing during changing body positions is believed to be due to
Episcleral venous pressure
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
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
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
No
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
No
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
No
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
