TABLE 2.
In vivo confocal microscopy of corneal nerves: a comparison of imaging modalities
| Type of Imaging | Principal of Image Capture | Aperture (μm) | Depth of field (μm) | Anterior stroma and subbasal nerve resolution* | Measurement of subbasal nerve density (mm/mm2) | Epithelial nerve imaging |
|---|---|---|---|---|---|---|
| In vivo confocal microscopy | Tandem scanning | 30.065 | 7.0 –11.065,210 | Poor resolution (nerves) High quality (stroma) 102,174 |
5.5 – 8.4 ± 2.064,65 | No 65,156 |
| Slit-scan (e.g., Confo-Scan) | Variable: e.g., 300.065 | 10.0 – 26.065,102 | High quality (nerves) 13 Poor resolution (stroma) 101,102 |
11.1 – 14.765,183 | Possible, but unreliable 156 | |
| Laser (e.g., HRT-RCM) | Variable | 4.0 – 7.065,210 | High quality (nerves) 180 | 21.7181 | No 65,201 |
HRT-RCM = Heidelberg Retina Tomograph with Rostock Cornea Module.
Statements regarding resolution have been extrapolated from several articles. Oliveira-Soto et al. 174 observed 57.1% of subbasal plexus nerve images obtained with a tandem scanning microscope were blurred with heterogenous reflectivity. Simultaneously, 50% of nerves in the subepithelial plexus of the anterior stroma exhibited beads, suggesting higher quality resolution in the stroma. Tandem scanning also offers good repeatability when measuring thickness of corneal layers. 102 Slit-scanning confocal microscopy demonstrates subbasal plexus resolution at values greater than or equal to histologic analysis. 102 However, poor repeatability of corneal layer thickness measurements suggest inadequate stromal resolution. 101,102 Laser scanning confocal microscopy exhibits high quality resolution with increased visibility of finer subbasal nerve branches. 180 Differences in nerve resolution may also be supported by the variable measurements of subbasal nerve density.