When you look through a red dot sight, do you see a clearly reticle, or something completely different? If you see a blurred dot that looks more like a star or a comma, or if you see multiple dots, you may have a defective optic or a red dot astigmatism.
In principle, each sight mounted on a firearm is an optical device, since its action is based on more or less complex optical phenomena. But it never even occurred to anyone to call an optical sight, consisting of a traditional fly and a whole. Fortunately, we will not talk about them and we will have to rack our brains only over the difference between “tubes with glasses,” whose action is based on a few more complex optical effects.