During the last few months I have had two antimetropic Rx’s that were originally unsuccessfully fitted with progressive lenses. The complaints were both centered on discomfort at near. One had been wearing progressives before, and the other was unknown if a new progressive wearer or not. Both cases had seen moderate Rx changes that had increased the amount of antimetropia.
The Rx for the first case:
R) -0.75 -1.00 X036 PD 31.9 seg hgt 22 2.50 add
L) +1.75 -1.25 X095 PD 32.5 seg hgt 22 2.50 add
After a review with the optician my first recommendation was to redo with a slab off. There was more than 3 diopters of power difference between the lenses and we would expect to see more than 3.75 diopters of prism imbalance at near. However the optician wanted me to come back with another option first before reverting to the slab. The pt. had not needed a slab before (about 0.75 less power difference in the 90) and it was felt the pt. would be put off by the cosmetic detraction of the slab.
With the slab option removed I was not certain that I could offer anything that would improve the pt.’s discomfort. We reviewed the pt.‘s previous pair which had the BC’s balanced and a split seg hgt, the R fit 1mm lower than the left. We agreed to balance the BC’s in the redo pair, however I did not think the 1 diopter change in front curve was going to help much with the issues at near. After a day or so for review I reached out to consult with the optician and suggested we run the R eye in a short corridor and the L eye to remain in a normal corridor length. This was done, dispensed and somewhat to my surprise relieved the pt. of their discomfort.
The Rx for the second case:
R) -1.25 -1.25 X094 PD 30.0 seg hgt 22 2.00 add
L) +1.25 -1.25 X077 PD 30.0 seg hgt 22 2.00 add
This came out of a separate office somewhat later and originally came to me to address the magnification differences between the two lenses. This was thought to be the primary driver for the non-adapt to the original progressives. However after some discussion with the optician it suggested that the pt.’s issues were more problematic at near vs. distance. I offered the same solution (along with aniso of the BC’s), a short corridor on the R and normal corridor on the L. This also was a successful dispense.
Both orders were re-run with full back side progressives but without any nod to POW.
The question then:
Without relieving the prismatic imbalance at near why is this working?
- Is binocularity still possible in this configuration?
- Is suppression and some form of monovision taking effect?
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