One of my cornea attendings explained this to me. If you are working with corneal transplant patients and using interrupted sutures, working in plus cylinder makes the most sense. The reason is that if the astigmatism is all corneal, you take out the suture in the meridian of the plus cylinder axis. (Remember, sutures flatten the cornea locally and steepen the cornea centrally.) This makes sense because if your refraction gives you Plano + 2.00 axis 180 you take out the suture at 9 and/or 3. (i.e. steeper K is in the 180 meridian, flatter K in the 90 meridian). Taking out a suture will flatten that meridian. I don't think this is the original reason why Ophthalmologists used plus cyl, but it does make sense. Also, it makes more sense for optometrists to use minus cylinder, especially when using rigid contact lenses (i.e. minus tear lens created to correct astigmatism). Just my take.
One other thing I will add for discussion. For pure corneal astigmatism, plus cylinder is adding power to the flatter K, and minus cylinder is subtracting power from the steeper K. But remember, power is 90 degrees away from cylindrical axis. This is important when trying to correlate K's with expected axis during refractions.
So... if you have K's of 40 D in the 180 degree meridian (horizontal) and 44 D in the 90 degree meridian (vertical) you would need to have a 4 D plus powerd cylindrical lens held in the 90 degree axis so that the power will be placed at the 180 degree meridian, thus neutralizing the astigmatism.
Oh, and IndianaOD, what is more crazy...the little optics training we get or the little pathology training you get? Just food for thought.
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