Tonometry (IOP)

• What does indentation measure in relation to the eyeball?

  Intraocular pressure (IOP) by direct pressure on the eyeball

  
• Who developed the Schiøtz tonometer and in what year?

  Schiøtz developed it in 1905
• How does applanation measure IOP?

  By determining the force necessary to flatten a corneal surface of constant size

  
• What is the Imbert-Fick Law in relation to applanation tonometry?

  • Pressure in a sphere filled with fluid is measured by the force that flattens the membrane.
  • Pressure = $\frac{W (g)}{A (mm^2)}$
  • W is the applanation force and A is the area.
• Why does the eye not truly meet the criteria of Fick's Law?

  Due to the presence of tissue tension forces and decreased internal volume during applanation
• What are the four forces acting when a tonometer probe contacts the cornea?

  Capillary attraction, force of the probe, fluid pressure behind the cornea, and corneal resistance
• What did Goldmann & Schmidt find regarding the circle of corneal applanation?

  If the circle equals a diameter of 3.06 mm, the tissue tension forces tend to cancel out
• What is tonometry used for?

  To measure the intraocular pressure (IOP) of a patient

  
• What are the two broad categories of tonometry techniques?

  • Contact tonometry (e.g., Goldmann, Perkins)
  • Non-contact tonometry (e.g., air-puff)
• What is the typical range for IOP in mmHg?

  Between 10 – 21 mmHg
• What are some long-term factors that affect IOP?

  Age, systemic blood pressure, race, body weight, ethnic origin, and seasonal variations
• What is diurnal variation in IOP?

  It refers to the fluctuation of IOP throughout the day, being highest in the morning and lowest in the evening
• How does corneal thickness affect IOP measurements?

  Thin corneas can underestimate IOP by up to 5.9 mmHg, while thick corneas can overestimate by up to 6.8 mmHg

  
• What short-term factors can influence IOP measurements?

  Body posture, exercise, state of the patient, cardiac and respiratory pulses, repeated measurements, medications, and lifestyle habits
• Who should have their IOP measured?

  All first-time patients, especially those over 40 years old, and those with risk factors for glaucoma
• What is the role of tonometry in glaucoma management?

  It is used to diagnose, manage, and assess the effectiveness of treatment for glaucoma
• What are some contraindications for tonometry?

  Corneal or conjunctival infections, significant corneal defects, known sensitivity to anesthetics, and severe ocular trauma
• What are the steps in the Goldmann tonometry procedure?

  1. Alcohol swab the probe and let it air dry.
  2. Explain the technique to the patient.
  3. Instill anesthetic and fluorescein drops.
  4. Position the Goldmann tonometer and adjust settings.
  5. Center the probe over the cornea and adjust the semicircles.
  6. Record the IOP measurement.
• What are the steps in the Perkins tonometry procedure?

  1. Follow similar steps as Goldmann but use a handheld tonometer.
  2. Hold the patient's eyelids without pressing on the eye.
  3. Adjust the illumination and measure IOP.
  4. Record the measurement as per Goldmann.
• What are the advantages and disadvantages of Goldmann versus Perkins tonometry?

  Goldmann is more stable, while Perkins is portable but may be less accurate
• What are some other types of tonometers mentioned?

  • Reichert TONO-PEN AVIA
  • i care tonometer
  • Air puff non-contact tonometer