Diopter/Iris blocker?

In my posting regarding the shot process the term "iris blocker" came up. I'm curious as to what the purpose/ advantage is to wearing these diopter type eyepieces. Are they strictly for use with red dots or are they used for irons as well?

A blocker, blocks vision from the non sighting eye, that way you keep both eyes open and dont have the muscle strain from trying to keep that eye closed. It also sharpens the dot and target. A adjustable iris goes in front of the aiming eye and as you close the iris down it can sharpen the sight picture with iron sights.

A right hand shooter usually has a right dominant eye. In this situation the shooter can shoot with both eyes open and the sights/dots will always be seen with the dominant eye. A left hand shooter usually has a left dominant eye.
 Some of the people of which I am one are right handed with a left dominant eye. In this situation you must block the dominant eye and use the non dominate eye, or hold the gun with the right hand and use the left dominate eye or switch hands and shoot left handed with the left eye. The blocker or diopter eliminates you from closing the dominant eye. The eye lid will fatigue during the match if you squint the dominant eye. The diopter should be translucent so that both eyes receive the same amount of light or you can not achieve optimal focus. 
 The iris is usually an adjustable aperture. Looking through a correct size aperture increases your depth of field of focus. ( making the front sight in focus). The aperture also gives a sight magnification. Try making a small hole with the pointing finger. Look through the hole at your computer screen. The letters should be in better focus and slightly larger especially if you need bifocals. The problem I have found with an aperture is that it is difficult to regain your sights and find your target when looking through the small hole.( in timed and rapid)
 I hope that explains it some.

People use blinders for the eye they are not aiming with and are used for both shooting dots and irons.

Irises and apertures are used to improve depth of field when shooting IRONS and are not needed for shooting with a red dot as those optics create the illusion that the dot and the target are on the same plane.

See www.eyepalusa.com for the aperture that I use.

I recently picked up and tried out a new pair of shooting glasses that I had made after reading on here about how to get a proper script for pistol shooting. I was fortunate to find an optometrist who is a shooter and had no issue with me bringing mine in to test. Long story short, it's so nice to be able to have the front sight in focus and I've already seen improvement in my scores. The best part is, my vision insurance covered everything!