How do positive and negative astigmatism differ?
January 6, 2012 6:36 AM Subscribe
Why are there two different methods (positive and negative) for recording astigmatism?
posted by dmd to health & fitness (3 answers total) 1 user marked this as a favorite
I'm led to understand that surgeons typically write positive cylinder numbers, while optometrists typically write negative cylinder numbers, and that negative values can be converted to positive ones by adding sphere+cyl to get the new sphere, and inverting the sign of the cyl to get the new cyl.
(1) What, historically, led to this situation?
(2) There seems to be some sort of difference in Lasik between "positive cylinder programs" and "negative cylinder programs", which seems to suggest that there's some actual difference. E.g., What is this talking about?