Aesthesiometer offers different way to measure functional recovery

Paris—Claes Feinbaum, OD, of Alicante, Spain, outlined the results of an ongoing study comparing a new type of aesthesiometer with a unit that has been the standard for 45 years to determine the accuracy and efficiency if the newer aesthesiometer.

Aesthesiometry is used to measure the functional recovery following refractive surgery. Dr. Feinbaum presented his data at a free paper session on refractive surgery at the European Society of Cataract and Refractive Surgeons meeting.

Until recently, the Cochet-Bonnet aesthesiometer was used among surgeons to measure functional recovery. In the study, a new aesthesiometer, the Non-Contact Corneal Aesthesiometer (NCCA), is used. The differences are that the NCCA measures the C-fibers of the cornea, because of their physical approximation to the stimulus, while the Cochet-Bonnet unit measures the A-delta fibers.

Dr. Feinbaum explained how the NCCA stimulates the cornea by releasing a controlled pulse of air toward the corneal surface. An air-jet is positioned 1 cm away from the corneal surface and a stimulus air-pulse is aimed at the eye. The subjects respond verbally whether they feel the stimulus. Depending on their responses, the pressure of the pulse is modified, and/or a new stimulus is presented.

In the study, 22 eyes were re-treated with LASIK. Measurements of corneal sensitivity were taken prior to re-treatment and postoperatively on days 1, 30, and 90. Twenty eyes were measured with the NCCA with a mean measurement of corneal sensitivity at 0.55 millibars, referred to as baseline measurement. Measurements were taken on 4 locations and no statistical difference was found between these.

The 22 re-treated eyes were followed for 90 days. No great threshold values were found pre- and postoperatively. The possible explanation is that the A-delta fibers are arranged parallel to the anterior corneal surface at the basal cell layer and responds to mechanical pressure. The C-fibers reach up to within one cell of the epithelial surface and since the NCCA sends out a thermal element, it responded to the temperature change.

The NCCA's ability to measure functional recovery was able to determine successfully a healthy cornea, with no previous disease. In tests, previous contact lens-wearing eyes have shown to reduce corneal sensitivity. Post-LASIK patients also have a reduced corneal sensitivity, with a similar pattern as the contact lens-wearing patient. Re-treatment corneas do not loose as much corneal sensitivity as suspected.