Vertical prism fitting ?

[Jaka]

In horizontal prism i would centre the lens on "rotation centre of the eye" (not the centre of pupil) and increase/decrease pupil distance for 0,25mm*pD.


What should i do in vertical prism? I guess PD is not questionable. It is what it is. I also think i should still increase/decrease height for 0,25mm*pD.

But should i use pupil centre or centre of rotation as hight ???

[fjpod]

How do you clinically determine the center of rotation of the eye? And how do you apply this to a location on the surface of a lens?

[Jaka]

I can't explain it better so i will just quote.

The optical centres of all single vision lenses should be dropped below pupil centre by 1mm for very 2 degrees of pantoscopic tilt. This ensures that the principal axis of the lens passes through the centre of rotation of the eye. There is an easier way to do this (tilting the person's head back so that the frame is perpendicular to the floor and finding pupil centre). While it is critical for aspherics it also applies to best form lenses, designed according to Tscherning's ellipses.
By doing this oblique astigmatism is kept to a minimum. It also helps an little with transverse chromatic aberration.
David Wilson