Let's consider this scenario. You have a SpecialEyes 54 Multifocal Toric contact lens patient return for his or her follow-up visit and the patient voices a desire for better near vision. You initially fit the patient in two near center lenses OU. You are confident that the refraction and contact lens Rx is accurate and the fit is optimal. It is in this scenario you may find it helpful to make a change in the near center zone size to address your patient’s chief visual complaint.
There are 2 parameters available to change in the 54 Multifocal Toric contact lens that will impact the custom multifocal zones- the near center zone and peripheral distance zone. Changing the peripheral zone impacts the progressive zone and the point at which full distance power is reached, leaving the near center zone unchanged. Changing the near center zone impacts the size of that zone and simultaneously impacts the progressive zone as well.
A change in the size of the near center zone will either improve your patient’s distance or near vision, depending on whether the zone size increases or decreases. If we take the example from above, noting the patient’s desire for better near vision, we would increase the near center zone by at least 0.20mm to create a better near visual result for the patient.
An increase in the near center zone from 2.0mm to 2.2mm will increase the area of near optics presented over the patient’s pupil while simultaneously increasing the rate at which the power progresses within the progressive zone. This change should improve your patient's near vision.
On the contrary, if your patient communicates a desire for better distance vision, this can be obtained by decreasing the size of the near center zone. This change will decrease the area of near optics presented over the patient’s pupil while simultaneously decreasing the rate at which the power progresses within the progressive zone. This change should improve your patient's distance vision and potentially their intermediate vision.
An improvement in intermediate and distance vision can also be obtained by changing the peripheral zone parameter. Factors such as pupil size and prescription must be taken into consideration when attempting to make a change to this zone. The next blog post will discuss the peripheral zone and rate of power progression in detail.
Conclusion:
To Improve Near Vision: Increase the near center zone by at least 0.20mm. The greater improvement needed in near vision, the larger the change you would make to create a positive outcome for your patient.
To Improve Distance Vision: Decrease the near center zone by at least 0.20mm. In certain situations, distance vision can and should be improved by altering the peripheral zone. It is important to note that a change in the peripheral zone must be made in conjunction with pupil size assessment and current peripheral zone size. There is more to come on the peripheral zone in the next blog post, which will explain this option in detail.
If you find that you are fitting a custom multifocal toric contact lens and have questions or would like assistance in making the multifocal toric contact lens zone change, please reach out to SpecialEyes’ consultation department.
Allison Salerno
Allison is a valuable member of the SpecialEyes team and brings with her dedication not only to SpecialEyes' customers, but her colleagues and the company's vision as well.