Theory Exam 2 Flashcards
Thick cornea ____estimates IOP
Thick overestimates IOP
Which tonometer can cause apprehension?
NCT
What is the area of the Goldmann probe?
3.06mm^2
Which pressure range can Perkin’s measure?
0-80 mmHg (similar to Goldmann)
What are corneal pulsations?
The IOP fluctuates because of the cardiac cycle
Overnight Goldmann sanitation is done with…
Hydrogen Peroxide
Which tonometer is dynamic contour tonometry?
Pascal
What can cause IOP lower than 7?
Retinal detachment, uveitis, wound leak, corneal penetration
How does environment change IOP?
IOP decreases with cold air
IOP increases with sudden gravity reduction
Which tonometers are good for supine patients?
Tonopen, Perkins, Transpalpebral tonometry requires supine.
Which tonometer uses disposable tip and measures impedance?
Icare
5-80 mm Hg is the pressure range for which tonometer?
Tonopen
What is pressure range for Icare?
7-50 mmHG
What fixation angle is required for transpalpebral tonometry?
45 degrees downward. You put the device on the upper eye through the eyelid.
What drops are used in Goldmann?
Sodium fluorescein and benoxinate combo
Which accuracy method is for tonopen? Tonopen avia?
Tonopen uses statistical coefficient (5% is good)
Tonopen avia uses confidence percepts? (95% is great)
Which tonometer has the highest pressure range?
Pascal with 1 to 200 mm Hg
How does Anterior Uveitis influence IOP?
It decreases IOP because of prostaglandins from inflammation , but then inflammation causes increased IOP (clogging TM)
What is the measurement range of the tonopen? The tonopen avia?
5 - 80 mmHg. Avia is 5-55 mmHg
How does a retinal detachment influence IOP?
It decreases IOP because RPE drains aqueous fluid
What are the 3 parts of the Goldmann tonometer?
Applanting probe, probe arm, measuring drum
What are the Goldmann assumptions?
Sphere should be dry, thin, perfectly elastic and flexible.
Displaced volume during process of applanation from within the sphere should be small in relation to total volume of sphere
Which tonometer takes 8-12 seconds for a measurement?
Pascal
How does systemic conditions affect IOP?
IOP increases
-As systolic level increases in hypertensive patients
-With systemic hyperthermia
-Obesity
-Increased pulse rate, and hemoglobin concentration
In response to hormones and steroids such as ACTH,
glucocorticoids and growth hormones
What is the pressure range for NCT?
0-60 mmHg
Goldmann ton is based on ____ principle
Imbert Fick
Which technique appears to measure IOP independent of Central Corneal Thickness?
Pascal
Which tonometer has auto-mode?
NCT
What kind of damage can happen from Goldmann reading?
Probe toe mark, lasts for only a couple of hours
Thick mires ___estimates IOP
Overestimates, subtract 1 or 2 from your reading
Thin mires ___estimates IOP
Underestimates, add 1 or 2 from your reading
What is Pressure Phosphene Tonometry?
You need patient input to report the phosphene. Good for glaucoma patients that don’t make sense. It has a limited scale. It touches the eyelid.
How does applanation tonometry differ from indentation tonometry?
Indentation records the force needed to indent the cornea (includes Air puff and obsolete Schiotz)
Applanation measures force to flatten cornea (coldmann, Perkins, Tonopen)
How does Pascal measure quality of pressure reading?
Q of 1-4
How can IOP change with eye movement?
IOP increases with blinking, lid squeezing, holding your eyes open, gazing upward
Functions of the aqueous:
Transport nutrients
Provide internal pressure
Refractive media
Which tonometer doesn’t need anesthetic?
Icare, NCT
Name tonometry method: components:
Micro strain gauge
Uses a 1.5mm transducer tip and microprocessor to calculate IOP
Self contained battery powered device
Tonopen
Name tonometry method: Advantages Very light, small, & portable Patient positioning Less apprehension Less affected by corneal thickness Can be used on peripheral corneas
Tonopen
Corneas thinner than ___um increase/decrease Goldmann reading?
Thinner than 540 decreases Goldmann reading.
Name tonometer: Diasadvantages Less stable Fixed magnification Cannot examine cornea before and after Easier to be off axis More difficult to get accurate readings Uses anesthetic
Perkins Tonometer
What is normal IOP? Normal difference between eyes
7-21. 4 between
How does Genetics, age, gender, refractive error, and race affect IOP?
Enlarged C/D and familial OAG. As age increases iop increases, women over 40 might have higher iop, myopes -10 or worse have higher IOPs (with axial length), and AA, asian, and latinos tend to have higher IOP.
At what age is corneal at adult thickness?
5-9 years
IOP influence: alcohol
Decreases
Which tonometer is second best gold standard?
Perkins tonometer
IOP influence: Marijuana
Decreases
IOP influence: LSD
Increases
What is serial tonometry?
Multiple measurement over the same day
IOP influence: tobacco
Increases
IOP influence: heroin
Decreases
Which part of the eye has the most resistance to aqueous outflow?
Juxtacanalicular portion of the trabecular meshwork. The aqueous ultimately goes to the episcleral venous area.
When is the tonopen ready to measure?
When it says ===
IOP influence: caffeine
Increases
What can cause IOP higher than 21?
Ocular HTN, Glaucoma
When is IOP the highest during the day? What short term IOP changes can happen?
It’s the highest at 3 am!
IOP increases in the supine position
IOP decreases with prolonged and brief exercise
IOP increases with physical straining (Valsalva’s maneuver)
IOP influence: Corticosteroids
Increases
IOP influence: fat free diet
Decreases
What is the mean IOP?
16 mm Hg
Which tonometer tends to overestimate IOP?
iCare, pascal, NCT in high range
Which tonometer will struggle with flat corneas?
Pascal
Name tonometry method: Disadvantages. Needs corneal anesthetic Expensive latex covers (and allergy potential) Require calibration (not a big deal) Less accurate at higher IOPs
Tonopen
