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Pre-regs should, if using a keratometer, ensure they find the principal meridians, but also ensure that they know the theory on both one and two-step design keratometers.
Some practitioners believe that steepening the Back Optic Zone Radius (BOZR), to a new value a third, or halfway, between the principal meridians, will create a more stable fitting lens, however, research tends to suggest that this is not a creditable method.
Patients who have difference in principal meridians from keratometer readings greater than 0.
Stabilisation is not necessary with this design of lens, since the lens radii should align with the principal meridians of the cornea.
Providing the ocular astigmatism is greater than the corneal astigmatism, it is possible to reduce the difference between the two principal meridians, and this will reduce the effect of the induced astigmatism.

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