A computer-assisted morphometric analysis of the organ of Corti

This paper describes a method for a computer-assisted morphometric analysis of the organ of Corti and presents normal morphometric data on the chinchilla cochlea. The computer-assisted light microscope system that we developed consists of commercially available equipment: an Olympus light microscope, Boeckler X, Y motorized stage micrometers, an IBM PC computer and a computer program written by the second author. The system was developed for the analysis of whole-mount, surface preparations of the organ of Corti. The procedure for producing suitable surface preparations for a computer-assisted analysis of hair cells was described in a previous paper (Santi, 1986). The analysis procedure requires 2 passes along the length of the basilar membrane. During the first pass, the system establishes an X, Y slide coordinate system and maps basilar membrane distance onto the coordinate system. This procedure was performed in approximately 10 min using an efficient, 3-point arc approximation method. During the second pass, the user scans along the length of the basilar membrane and measures organ of Corti structures (e.g., hair cell dimensions) or records abnormal or missing hair cells. In addition to providing distance along the length of the basilar membrane, the system could also determine which hair cell row the user was examining. Thus, recording damaged and missing hair cells consisted of merely pressing the appropriate footpedal to indicate the type and degree of hair cell damage. After assessing hair cell damage, a cytocochleogram with an accompanying table of descriptive statistics was produced. Since the X, Y coordinate system for each slide was stored on a disk along with its corresponding basilar membrane distance map, slides could be removed and later reevaluated without the loss of previously obtained data. Normal morphometric data on the chinchilla organ of Corti consisted of cell dimensions within the reticular lamina and a two-dimensional graphical reconstruction of the curvature of the basilar membrane.