TargetTalk

Why is my rear sight vertical edge look crooked when in reality they are straight? It bugs the hack out of me to see that crooked vertical edge of rear sight in my front/rear sight alignment. I look at the rear sight close up. Rear sight is a perfect square notch.

Can someone explain this to me?

Contact an Opthalmologist , there are many retinal and macular conditions that can cause such deviations in sight. Eliminate one thing at a time.

Astigmatism can cause the rear sight notch to appear trapezoidal in shape.

Dp you wear glasses?

I wear transitional lens for myopia/presbyopia.

Another possibility is diffraction. Very narrow sights bend the light beam, the same way the famous pencil bends in the water glass...

From Merriam Webster:

a modification which light undergoes in passing by the edges of opaque bodies or through narrow slits or in being reflected from ruled surfaces and in which the rays appear to be deflected and produce fringes of parallel light and dark or colored bands

Chears.

I also wear progressive lenses, but I CAN'T use them for shooting. Have you considered dedicated shooting glasses with single-vision Rx?

Yes, I do wear my old single vision lens for shooting.

But the vertical edge bend is still apparent.

I think Jacques may be close to the money on this one.
You may be getting light refaction because you are looking through your lens at an angle.
In a normal stance a right handed shooter has his head turned to the right and is looking through the lens at an angle. Shooting glasses enable the lens to be turned to get the optimum sight picture through the centre of the lens which should be at right angles to the line of sight.