Effect of CHIR 99021 on the viability of orbital fibroblasts. Orbital fibroblasts of GO and non-GO patients were seeded in 24-well culture plates, 1 × 105 cells per well. Various concentrations (0–20 µM) of CHIR 99021 were applied to wells for 18, 24, 48, and 72 hours, and an MTT assay was conducted to test cell viability. Results are expressed as a percentage of untreated control and are presented as mean ± SD. Assays were performed at least three times in triplicate. Differences between treated and untreated cells are indicated (*P < 0.05).