A new video pachometer

Many studies of the cornea would benefit from a simple, objective method to measure corneal thickness. In this study, a new optical pachometer based on video and computer technology was designed and tested.

The slit beam of a photographic slit lamp was monitored with a video camera through one half of the biomicroscope. When the slit was properly aligned with the cornea, the operator triggered a flash, and one video frame that included the flash was captured. A custom software package detected epithelial and endothelial edges. Corneal thickness was calculated from the median corneal image width and image widths from similar measurements of contact lenses with known thicknesses. Corneal thickness was measured in 25 subjects by using this new instrument and was compared to thickness measured by using a conventional Haag-Streit pachometer.

Corneal thickness in the 25 subjects measured on the new instrument was 512+/-20 microm and 515-/+21 microm in the right and left eyes, respectively (mean+/-SD). Thickness of the same corneas measured on the Haag-Streit pachometer was 530+/-22 microm and 534+/-20 microm in right and left eyes, respectively. The average SD of 10 consecutive measurements was 6.6 microm and 6.7 microm on the video and Haag-Streit pachometers, respectively (n = 50 corneas).

The video pachometer provides a fast, objective means of measuring corneal thickness. It is simple to use and provides precision equal to that of the Haag-Streit pachometer.