Withanoside VI from Ashwagandha (Withania somnifera) acts as an HSP90 co-chaperone modulator, stabilizing misfolded opsin proteins in blue cone monochromats. By enhancing the folding capacity of the endoplasmic reticulum through HSP90β upregulation, this withanolide prevents ER stress-induced cone cell death and potentially restores partial opsin function.