With astigmatism, you will see the same effect focusing on a reticule as for an RDS, except it is less obvious. Basically, you see double, and may still find precision shooting difficult without corrective lenses.

An RDS is focused between 80 yards and infinity, so there will be no parallax at that distance or beyond. Parallax is where the POA changes when you move your eye point from side to side. A stronger diopter lens will make the subject appear closer, but this will have no affect on the accuracy. You can shoot with one or both eyes open (both gives you better acquisition and situation awareness). You can even shoot accurately with the lens caps on the RDS closed with your weak eye open.

In a regular scope, you should have separate focusing for the reticule (i.e., the eyepiece) and the target, especially if you have vision problems. This is sometimes called "side focusing" because the knob is on the center turret.

Another option is first plane v second plane focusing. In first plane, the reticule is magnified along with the zoom level. In second plane, the reticule is constant, but may be hard to use with distant targets because thicker lines are needed. Second plane reticules are needed if you use mil markings to compensate for wind or range.