Podcast
Questions and Answers
What should be used to avoid disrupting the epithelium of the cornea during the procedure?
What should be used to avoid disrupting the epithelium of the cornea during the procedure?
- Excessive illumination
- Cotton tip applicator against the globe
- Ghost mires (correct)
- Direct pressure with the probe
What is the ideal thickness of the mires during the procedure?
What is the ideal thickness of the mires during the procedure?
- 0.25-0.30 mm (correct)
- 0.10-0.15 mm
- 0.30-0.35 mm
- 0.20-0.25 mm
What should be done if the mires appear unequal during the procedure?
What should be done if the mires appear unequal during the procedure?
- Change the light source
- Proceed with the measurement regardless
- Adjust the slit lamp until they are equal and centered (correct)
- Stop and restart the entire procedure
According to Imbert-Fick Law, how is the pressure inside an ideal sphere expressed?
According to Imbert-Fick Law, how is the pressure inside an ideal sphere expressed?
What position should the patient's head be in during the procedure?
What position should the patient's head be in during the procedure?
What is the primary disadvantage of using the Rebound Tonometer for IOP measurement?
What is the primary disadvantage of using the Rebound Tonometer for IOP measurement?
Which factor is not a limitation of the Transpalpebral Tonometer?
Which factor is not a limitation of the Transpalpebral Tonometer?
How does the Rebound Tonometer determine the IOP based on the probe's movement?
How does the Rebound Tonometer determine the IOP based on the probe's movement?
Which of the following methods can record IOP?
Which of the following methods can record IOP?
What is the role of the pneumatic system in NCT systems?
What is the role of the pneumatic system in NCT systems?
What principle does the MacKay-Marg tonometer utilize?
What principle does the MacKay-Marg tonometer utilize?
Which device is particularly useful in non-cooperative patients or children?
Which device is particularly useful in non-cooperative patients or children?
In which situation is the Transpalpebral Tonometer particularly useful?
In which situation is the Transpalpebral Tonometer particularly useful?
What advantage does the Pascal-Dynamic Tonometer (DCT) provide over traditional applanation methods?
What advantage does the Pascal-Dynamic Tonometer (DCT) provide over traditional applanation methods?
What is the primary use of disposable latex covers in the Tonopen?
What is the primary use of disposable latex covers in the Tonopen?
How does the IOP estimation change after LASIK and PRK?
How does the IOP estimation change after LASIK and PRK?
Which characteristic of the MacKay-Marg tonometer helps identify the force of application?
Which characteristic of the MacKay-Marg tonometer helps identify the force of application?
What is the function of the piezoresistive pressure sensor in the Pascal tonometer?
What is the function of the piezoresistive pressure sensor in the Pascal tonometer?
How many readings does the Tonopen typically take to provide an average?
How many readings does the Tonopen typically take to provide an average?
What should be done first for contact lens wearers before a procedure involving NaFl?
What should be done first for contact lens wearers before a procedure involving NaFl?
How is intraocular pressure (IOP) affected by WTR astigmatism?
How is intraocular pressure (IOP) affected by WTR astigmatism?
What is the primary cause of inaccurate readings when using the probe to measure IOP?
What is the primary cause of inaccurate readings when using the probe to measure IOP?
What is a recommended treatment for superficial punctate keratitis (SPK)?
What is a recommended treatment for superficial punctate keratitis (SPK)?
When is it preferable to use Non-Contact Tonometry (NCT) instead of Goldmann Applanation Tonometry (GAT)?
When is it preferable to use Non-Contact Tonometry (NCT) instead of Goldmann Applanation Tonometry (GAT)?
What time of day do IOP readings tend to be highest?
What time of day do IOP readings tend to be highest?
How much can IOP fluctuate over 24 hours?
How much can IOP fluctuate over 24 hours?
What does a diurnal curve measure in glaucoma patients?
What does a diurnal curve measure in glaucoma patients?
What IOP difference between eyes should raise concern?
What IOP difference between eyes should raise concern?
What can be a result of poorly rinsing the probe after measurement?
What can be a result of poorly rinsing the probe after measurement?
How can pressure (P) be determined in the context of the cornea?
How can pressure (P) be determined in the context of the cornea?
Which factor is NOT listed as a potential error in Goldmann tonometry?
Which factor is NOT listed as a potential error in Goldmann tonometry?
What is the effect of thinner corneas on Goldmann Applanation Tonometry (GAT)?
What is the effect of thinner corneas on Goldmann Applanation Tonometry (GAT)?
What is a characteristic of Goldmann tonometry concerning corneal thickness?
What is a characteristic of Goldmann tonometry concerning corneal thickness?
Which of the following statements about Goldmann tonometry is true?
Which of the following statements about Goldmann tonometry is true?
What influence does the Valsalva maneuver have on intraocular pressure?
What influence does the Valsalva maneuver have on intraocular pressure?
Which factor could contribute to a falsely high IOP during Goldmann tonometry?
Which factor could contribute to a falsely high IOP during Goldmann tonometry?
How does the presence of fluorescein affect the measurement in Goldmann tonometry?
How does the presence of fluorescein affect the measurement in Goldmann tonometry?
In which situation is it advised to finalize a patient's refraction prior to GAT?
In which situation is it advised to finalize a patient's refraction prior to GAT?
Which condition is described as ocular hypertension?
Which condition is described as ocular hypertension?
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Study Notes
Disinfecting Solutions
- Opticide: Disinfectant that does not damage the probe; requires 3 minutes of immersion.
- Isopropyl alcohol 70%: Potential to damage probes; not as effective against Hepatitis B and C; requires rinsing and tapping dry.
Tonometer Procedure
- Patient positioning: Must keep head against forehead and chin on chinrest for accurate measurements.
- Fixation targets: Different targets for each eye (OD and OS).
- Slit lamp adjustment: Set measuring drum to 1, light source at 60-65° temporal to the probe.
- Observe and position probe close to cornea without sudden movements.
Probe Alignment and Use
- Before touching the cornea, ensure probe is centralized.
- Use cotton tip applicator to hold eyelids if needed, avoiding pressure on the globe.
- Look for ghost mires (pale blue/gray semicircles) to ensure alignment and avoid epithelial disruption.
Mires Measurement
- Ideal mire measurements: 0.25-0.30 mm; thick mires lead to falsely high readings, thin mires yield falsely low readings.
- Align mires, if misaligned, follow the larger one for adjustment.
Imbert-Fick Law
- States pressure inside a fluid-filled sphere is determined by the force needed to flatten the sphere's surface divided by the area flattened.
- Variables like irregularity of the cornea may affect results.
Goldmann Tonometry Errors
- Various factors influence accuracy: fluorescein amount, eye movements, and corneal conditions.
- Patient anxiety or specific eye conditions can lead to inaccurate IOP measurements.
Corneal Thickness Impact
- GAT most accurate with average thickness (~550 μm).
- Thinner corneas may underestimate IOP; thicker corneas may overestimate.
- Conversion tables for corneal thickness not widely used due to lack of consensus.
GAT Application
- Performed prior to dilation; critical for glaucoma management.
- Recommended to finalize refraction before GAT due to anesthesia-induced blurry vision.
Measurement Considerations
- IOP varies throughout the day, highest readings in the early morning.
- Discrepancies larger than 4mmHg between eyes may indicate underlying conditions.
Perkins Tonometer
- A handheld version of Goldmann tonometry.
Advanced Tonometer Systems
- MacKay-Marg/Tonopen: Electronics convert transmitted pressure to mmHg; useful for non-cooperative patients.
- Pascal Tonometer: Uses contour matching and piezoresistive sensors; accounts for pulsatile IOP variations.
- NCT: Utilizes pneumatic air puff for measurements, includes optoelectronic mechanisms.
- Diaton (Transpalpebral Tonometer): Measures IOP through eyelid pressure; useful for special needs populations.
Rebound Tonometer (iCare)
- Utilizes a magnetized probe to measure deceleration speed on contact; least contact time required.
- Probes are disposable, allowing easy hygiene without disinfection.
Flatness and Astigmatism Considerations
- Astigmatism impacts IOP readings; adjustments based on K readings help minimize errors.
- Post-procedure examination for keratitis or abrasions is important to prevent complications.
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