It can be demonstrated by retinoscopy or keratometry that the principal meridians
of the cornea, as a whole, are not perpendicular to one another.
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.
Dorsher concluded that, The marked degree of correspondence noted in this qualitative study between the distributions of the anatomically derived myofascial meridians to those of acupuncture Principal Meridians is unlikely to be coincidental'.
Peter Dorsher's study of Myers' nine myofascial meridians revealed that, 'In 8 of 9 comparisons, there was substantial overlap in the distributions of the anatomically derived myofascial meridians with those of the acupuncture Principal Meridian distributions'.
Corneal factors include the difference in the radii of curvature of the principal meridians.
Astigmatism is also classified on the relationship between the two principal meridians as regular (when two principal meridians are perpendicular to each other) and irregular (when the two principal meridians are not perpendicular to each other).
Astigmatism was classified on the basis of relationship between the two principal meridians as regular (when two principal meridians are perpendicular to each other) and irregular (when the two principal meridians are not perpendicular to each other).
The township numbers east or west of the Principal Meridians are designated as ranges, whereas the numbers north and south of the Base Line are tiers.
The translation is "the northwest quarter of the southeast quarter of section 14 in township 6 north and range 11 west of the 6th Principal Meridian.
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.