Measuring the Refractive Index of Bovine Corneal Stromal Cells Using Quantitative Phase Imaging.
The cornea is the primary refractive lens in the eye and transmits >90% of incident visible light. It has been suggested that the development of postoperative corneal haze could be due to an increase in light scattering from activated corneal stromal cells. Quiescent keratocytes are thought to produce crystallins that match the refractive index of their cytoplasm to the surrounding extracellular material, reducing the amount of light scattering. To test this, we measured the refractive index (RI) of bovine corneal stromal cells, using quantitative phase imaging of live cells in vitro, together with confocal microscopy. The RI of quiescent keratocytes (RI = 1.381 ± 0.004) matched the surrounding matrix, thus supporting the hypothesis that keratocyte cytoplasm does not scatter light in the normal cornea. We also observed that the RI drops after keratocyte activation (RI = 1.365 ± 0.003), leading to a mismatch with the surrounding intercellular matrix. Theoretical scattering models showed that this mismatch would reduce light transmission in the cornea. We conclude that corneal transparency depends on the matching of refractive indices between quiescent keratocytes and the surrounding tissue, and that after surgery or wounding, the resulting RI mismatch between the activated cells and their surrounds significantly contributes to light scattering.
Optometry and Vision Sciences, Cardiff University, Cardiff, UK.
Steven J
SJ
Gardner
Optometry and Vision Sciences, Cardiff University, Cardiff, UK.
Nick
N
White
Optometry and Vision Sciences, Cardiff University, Cardiff, UK.
Julie
J
Albon
Optometry and Vision Sciences, Cardiff University, Cardiff, UK.
Carlo
C
Knupp
Optometry and Vision Sciences, Cardiff University, Cardiff, UK.
Christina S
CS
Kamma-Lorger
Optometry and Vision Sciences, Cardiff University, Cardiff, UK. Electronic address: meekkm@cf.ac.uk.
Keith M
KM
Meek
D000818:Animals; D002417:Cattle; D048429:Cell Size; D002478:Cells, Cultured; D060527:Corneal Keratocytes / Q000502:physiology / Q000528:radiation effects; D003319:Corneal Stroma / Q000166:cytology / Q000502:physiology* / Q000528:radiation effects*; D003593:Cytoplasm / Q000502:physiology / Q000528:radiation effects; D018613:Microscopy, Confocal; D008954:Models, Biological; D061848:Optical Imaging / Q000379:methods*; D012542:Scattering, Radiation; D017154:Stromal Cells / Q000502:physiology