Hi,
The common diagram showing why tilt needs to be compensated does make some sense but could anyone answer a few questions I have regarding this.
1. The line of gaze doesn't change so by decentering the lens there will be induced oblique astigmatism so does this induced oblique astigmatism counteract the OA due to the tilt?
2.If not then it seems to me that the eye would have to rotate downwards in order to obtain the best vision which would seem impossible to view something properly directly in front of them!
3. Decentering the lens will induce prism. Assuming the eye rotates towards the apex then this would seem acceptable for a minus lens for question/statement (2), but worse for a plus lens.
4. At what point should Anisometropia be taken in to account? Taking a fairly common RX and frame combo... RE +7.00 LE +5.50, tilt of 12 deg. vertical decentration would be 6mm which would induce prism (using approx. prentices rule) of RE 4.2D LE 3.3D. Which would be beyond the theoretical limit of tolerated vertical prism (my books say between .5 to 0.75 D).
5. Jalie remarks that in Aspheric lenses it is even more important that the pole of the aspheric lens coincides with centre of rotation again if the axis of gaze doesn't change then how can this be so with a vertically decentred lens?
Thanks
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