The "Gold Standard" in Corneal Thickness Measurement
Figure 1-Corneal Waveform
Up until now the process of ultrasonic pachymetry has involved the following steps:
- Place anesthetic eye drop in patient's eye and wait for the anesthetic to take effect.
- Start the pachymeter and gently bring the pachymeter transducer into contact with patient's cornea.
- 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:
- 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.
- 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.
- 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.
- 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.
- 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.
|
