Asymmetrical Add to achieve balanced reading experience? Help.

Can one of the experts here please tell me if there is a condition that results in the requirement of an asymmetrical add for reading in an over 50 patient? Once the correct script is determined with the eyes relaxed at optical infinity is it possible that some can require a greater add on one eye to achieve balanced sharpness / focus at reading distance? In this case the script is:

OD +1.50 Cyl 0.00 Add +2.00
OS +1.25 Cyl -0.25 Axis 90 Add +2.00

At optical infinity this script works perfectly. But in the reading portion of the bifocal the patient is claiming that the right eye is blurry. Using trial lenses over the glasses that were made with the prescription (yes it was remeasures to ensure accuracy) the patient requires +.50 over the right to get both eyes to appear balanced with the same sharpness. Can one eye have a stiffer lens? Or is there some other phenomenon that may be at play. Thank you for your time and expertise.

 

Several factors could contribute to the need for an asymmetrical add or different power between the eyes for reading, even when the distance correction appears balanced.

1. Presbyopia, the age-related loss of near-focusing ability, can affect individuals differently in each eye.
2. Astigmatism can affect the clarity of vision at various distances. The presence of astigmatism, especially if it differs between the eyes, can contribute to variations in the perceived sharpness at near distances.
3. Differences in how the eyes work together (binocular vision) can influence the perceived clarity of vision. This includes factors such as eye dominance and the coordination of the eye muscles.