Progressive lenses were an amazing step forward in lens technology; however, as we continue to innovate, there is more to learn, and more ways we can refine our lens designs.
For example, how often are your patients underwhelmed or uncomfortable with their new progressive lenses? It’s relatively common and yet sometimes difficult to pinpoint why– especially after what seemed a successful eye exam.
Here’s what could be going on and how to fix it with the right eye technology.
Handling binocular disparity in presbyopic patients
Currently, 7 in 10 presbyopes have different prescriptions between their left and right eyes1, and this leads to a frustrating amount of eye strain symptoms, especially when reading.
The smallest amount of binocular disparity (when there is a difference between your two eyes prescriptions) means that light passing through each lens will be refracted differently. Therefore, the prismatic effect of each lens will be different. The result is a visual imbalance that can cause asthenopic complaints such as unstable blurred vision, tired and burning eyes, and headaches.
In other words, presbyopic patients need their brains to work harder to even out the images processed by each eye– because their eyewear provides slightly different images.
Single vision lenses create less strain because the wearer can adjust objects for near vision (they simply use the central position of the lens). On the other hand, progressive wearers need to use different areas of the lens depending on the activity.
This creates discomfort, and a wearer’s vision is only clear when covering one eye or the other. Binocular balance in presbyopes is possible now with our patented Binocular Harmonization Technology™ (BHT).
Balancing presbyopia with Binocular Harmonization Technology
Binocular Harmonization Technology is the latest ophthalmic lens tech that takes into account binocular disparity. By adjusting the progressive corridor lengths, power distribution and lens thickness, maximum binocularity is achieved at near. It uses five new measurements in the Binocular Eye Model:
1. Binocular Clearness Index: how clearly the wearer sees an image through the spectacle lenses.
2. Convergence Difference between R/L:shows whether the two lens combinations force the wearer to apply either convergence or divergence as a function of the object distance, the power, the power difference and the prismatic difference (due to the power difference).
3. Accommodation Demand Difference between R/L: the amount of accommodation an eye requires to view an object at any distance.
4. Magnification Difference between R/L: the difference in spectacle lens magnification for the right and left eye.
5. Vertical Prismatic Difference between R/L: the different prismatic effects of the pair of lenses in vertical direction.
By taking into account the differences between the two eye prescriptions and the 5 types of measurements above, we can adjust each lens to equalize image size and image position. This creates harmony between the two eyes and stable binocular vision at near. The patient’s eyes no longer have to self-correct, reducing their eye strain symptoms.
Learn more about the five primary elements of BHT that lead to optimal distance vision and full reading support.