  Knowledge of optical properties, such as the refractive index (RI), of
biological tissues is important in optical imaging, as they influence the
distribution and propagation of light in tissue. To accurately study the
response of cancerous cells to drugs, optimised imaging protocols are required.
This study uses a simple custom-built spectral domain optical coherence
tomography (OCT) system to conduct RI measurements of multicellular spheroids,
three-dimensional \textit{in-vitro} culture systems, of the cell line HCT116.
The spheroid RIs are compared to study the effect of growth time. To improve
confocal microscopy imaging protocols, two immersion media (glycerol and
ScaleView-A2) matching the spheroid RIs were trialled, with the aim to reduce
the RI mismatch between the spheroid and the immersion medium and thus
improving imaging depth with confocal microscopy. ScaleView-A2 (n = 1.380)
aided in achieving greater depths of imaging of the multicellular spheroids
under confocal microscopy. This improvement in imaging depth confirmed the
utility of our RI measurements, proving the promising outlook of OCT as a
complementary tool to microscopy in cancer research.
