Progressives: One Lens Change or Redo.February 1, 2016
This is an area where a light bulb should go off in everyone’s head when it presents itself. We should all know that progressives have some amount of prism thinning. The problem is that sometimes we order a one lens RX change but when the lens comes back the patient is still having problems. We may have solved the original problem (Rx change, PD adjustment, fitting height adjustment, etc.) but caused a new one (the prism thinning does not match in the pair of lenses).
Let’s review how prism thinning is calculated.
-The Optimal Prism Thinning computer program looks at both lenses and calculates a single amount of prism thinning that will work in both lens.
-When the program only has the information of one lens, it calculates the best prism thinning for just that one lens. Depending on the other lens, it may or may not match. If the difference of prism between the pair of lenses is off too much, the patient could have some discomfort especially in the distance gaze.
How do we prevent this? There are a couple of different ways.
- When you are ordering a one lens Redo/Change, check in a lensometer the amount of prism thinning in the present pair of lenses and request that specific amount of prism thinning in the new lens. Make sure you give the direction of the prism too.
- When you are ordering a one lens Redo/Change, write the prescription of the other lens down on the Rx and note that it is for “Information Only” for prism thinning. This way the computer program will look at both lenses and calculate the correct amount of prism thinning for your lens.
Robert Hughbanks ABOC, HOAA- Manager of Training and Development