The SpecialEyes 54 Toric Multifocal contact lens, near center design, is unique in that the practitioner has the ability to control the rate at which the power progresses from full near power in the middle of the contact lens to full distance power at a set diameter value in the periphery. By controlling the rate at which the power progresses or transitions, you can impact the patient’s intermediate vision. By controlling the point at which full distance power is reached in the periphery of the toric multifocal contact lens, you can impact the patient's distance vision.
Within this custom aspheric toric multifocal contact lens, there are two customizable parameters that will impact the rate at which the power progresses, the near center zone and peripheral zone. As the prior blog post discussed, changing the near center zone not only impacts the area of near optics present over the patient’s pupil, but also slightly changes the rate at which the power progresses within the progressive zone. On the other hand, changing the peripheral zone directly impacts the rate at which the power progresses within the progressive zone and also alters the point at which we reach full distance power in the periphery of the contact lens.
Let’s delve into what happens to the powers when we customize or alter the peripheral zone diameter value.
By increasing the peripheral zone diameter value, the rate at which the power progresses will decrease causing the powers to become more spread out. This effect will improve intermediate vision for the patient. It will have an impact on distance vision as well, but we would need to reference pupil size to see if it would have a positive or negative effect. If the pupil size was 4.5mm and the peripheral zone was changed from 4.0mm to 4.5mm you should expect a slight decline in distance vision but an increase in intermediate vision. The slight decline in distance vision is due to a decrease in the amount of full distance optics being placed over the patient's pupil diameter area.
On the contrary, decreasing the peripheral zone diameter value will increase the rate at which the power progresses, causing the powers to be closer together. It will also cause the contact lens to get to full distance power quicker. Consider this scenario, a patient has a 4.0mm pupil and the peripheral zone is set to 4.0mm. The patient voices a desire for better distance vision. The patient's visual acuity is 20/40 OU and 20/40 OD and 20/50 OS. It is in this example where you would want to decrease the peripheral zone to 3.5mm to improve distance vision. This change would enable the lens to get to full distance power quicker and thus more distance optics would be placed over the patient's pupil diameter area.
Deciding to make a change to the peripheral zone diameter value, or any zone for that matter, is relative to the patient’s pupil size in regular room light, as well as other factors such as visual acuity results, prescription, and the patient’s chief visual complaint. Changing a zone to impact the rate at which the power progresses within the progressive zone or the point at which full distance power is reached in the periphery of the lens must be made after assessing these multiple factors, especially pupil size. Please feel free to reach out to the SpecialEyes consultation team for troubleshooting assistance or any questions you may have in regard to multifocal zone changes as it relates to pupil size.
You will learn more about the impact pupil size has on our decision to make a zone change in an upcoming blog post, so stay tuned! For further information and learning about our custom toric multifocal contact lens we highly encourage you to visit The Learning Center on our website and sign up for our multifocal email course!
Thanks for tuning in,
Staci Blackwell is an account manager at SpecialEyes. She has been with the company since 2007 and carries with her a vast knowledge of the company’s products and the features of those products that can benefit your most discriminating contact lens patient.