I myself for example, have a visual acuity without correction of 20/20 in good lighting conditions, and drops to 20/30 in the dark, but I do have a small correction, mainly astigmatism. If I wear my glasses, my visual acuity goes up to 20/10 in good lighting conditions, and to about 20/15 in the dark.

Why does VA drops so much in the dark for people with refractive errors?

For example my Rx is: * OD: -0.25SPH * OS: -0.75CYL

It is very minor Rx and I barely notice it at daytime, I can see 20/20 comfortably even without my glasses. Difference with/without glasses is quite small.

At nighttime though (and most at the dusk), I subjectively feel I see much worse and I also notice a significant difference with/without my glasses.

Why this happens?