  We give some remarks on exact quantization conditions associated with
quantized mirror curves of local Calabi-Yau threefolds, conjectured in
arXiv:1410.3382. It is shown that they characterize a non-perturbative
completion of the refined topological strings in the Nekrasov-Shatashvili
limit. We find that the quantization conditions enjoy an exact S-dual
invariance. We also discuss Borel summability of the semi-classical spectrum.
