Last week I came across this question in a forum, which I have always wondered why, and leave it to the Optical Yoda, Van Rue to answer and allowed me to share:
Ages ago, Cylinder was ground on the front of all lenses beginning around 1835, with sphere on the back… so Cyl was noted in plus form by Ophthalmology, since is was being formalized around this same time.
However, in the early 1900’s Dr. A. Estelle Glancy and Dr. Edgar Tillyer proved this is was optically a poor choice, and that cylinder should be on the back with the sphere. Optometry was being formalized around this time, and decided a backside cyl notation in minus was more appropriate. (Although we have known for over 100 years that nothing should be on the front of lens, it took 50 years for plus cyl to disappear from lenses, and will take another 50 for OMD’s to stop using it. (side note, progressive are cylinder and its the same reason the add should also be on the back, NOT the front of a lens).
Although an Optician named Foster was the first to fabricate cyl on the front of a lens around 1835 in Ipswitch, England, its not known how that info was shared and how fast the idea spread.
We shouldn’t be too hard on the OMDs, it took about 5 years and 11 volumes of blank books to Tillyer and Glancy to prove the mathematically the inferiority of front side cyl, but it boils down to keeping the visual axis of the cyl and sphere as close as possible together.
Even though the industry started shifting away from plus cyl in the early 1900s, it took forever. There were still plus cyl stock lenses up until the early 1970s, and stock lenses to date are still marked in plus and minus cyl.
What are your thoughts? Which cyl does your OD or OMD use?
February of 2020 and anonymous Ophthalmologist submitted this:
Ophthalmologists prefer plus cylinder for a number of non-historical reasons.
When planning surgery, incisions placed at the plus cylinder axis will reduce astigmatism. Plus cylinder notation is the simpler choice.
Also, sutures removed along the plus cylinder axis will reduce astigmatism.
For refractive surgery, negative cylinder is actually more helpful and you will find most refractive ‘OMD’s’ use negative cylinder.
In summary, for prescribing glasses, negative cylinder is the more helpful notation. For surgical planning, plus cylinder is typically more helpful. They can be quickly interchanged so really any preference is more for convenience’s sake.