Contact Lens Pachymetry
The "Gold Standard" in Corneal Thickness Measurement


Figure 1-Corneal Waveform

Up until now the process of ultrasonic pachymetry has involved the following steps: 

  1. Place anesthetic eye drop in patient's eye and wait for the anesthetic to take effect.
  2. Start the pachymeter and gently bring the pachymeter transducer into contact with patient's cornea.
  3. Pachymeter takes corneal thickness measurements by sending ultrasonic pulses towards the cornea and it measures the time it takes for the posterior corneal spike to come back to the ultrasonic transducer. This time is then converted to thickness measurement by using the known value of speed of sound through human cornea.

Contact Lens Pachymetry is the process of measuring the corneal thickness through a contact lens placed on the patient's eye. Contact lens Pachymetry sets the "Gold Standard" in corneal thickness measurement by removing errors associated to identifying the location of anterior cornea as well as minimizing any indentation of cornea due to probe contact. Contact Lens Pachymetry improves upon the traditional pachymetry in the following ways: 

  1. Removing the need for anesthetizing the patient's eye.
  • Since the transducer is no longer coming into direct contact with the patient's eye it is no longer necessary to anesthetize the eye.
  1. Removing errors associated with uncertainty in the location of the initial corneal spike. Figure above shows the clipping that occurs in the ultrasonic reflection from the transducer/cornea interface. This clipping is a possible source for error since it creates an uncertainty in the actual location of the anterior cornea.
  2. Figure above shows the ultrasonic reflections from the anterior corneal interface are no longer saturated due to the presence of the contact lens and the actual location of the anterior cornea can be resolved accurately by the location of the highest peak.
  3. Minimizing any errors associated to corneal indentation. A soft contact lens material may under go some compression but this compression is not transferred to the cornea and it does not effect the corneal thickness measurements.
  4. Minimizing the risk associated with corneal abrasions and infections.
  • Since the transducer is no longer coming into direct contact with the patient's eye risks associated to scaring, abrasions and possible infections are minimized.

For those of you familiar with immersion biometry these advantages should be self evident.