When it comes to determining where the bifocal line should be placed on your glasses, there isn’t a definitive answer. The ideal position of the bifocal line is highly dependent on your personal preferences and the specific activities you engage in while wearing your glasses. This discussion specifically applies to lined bifocals, such as Flat Top (FT-28) bifocals or Executive Bifocals, which have distinct visible lines separating the different lens powers.
A standard guideline for placing a lined bifocal is to set the line approximately 3mm below the center of the frame. To calculate this, start by measuring the total height of your frame from top to bottom. For instance, if your frame is 40mm tall, you would find the center at 20mm. Subtracting 3mm from that center point would place your bifocal line at 17mm from the bottom of the frame. This serves as a rough estimate for a standard segment height, which is often a good starting point for most people.
However, this guideline is just that—a starting point. Depending on your lifestyle and specific needs, you may find that adjusting the bifocal line up or down is necessary. For example, if you’re making sunglasses and don’t plan on using the bifocal portion frequently, you might prefer to position the line lower so it stays out of your primary field of view. Conversely, if you spend a lot of time reading or working on tasks that require close-up focus, you may want the bifocal line positioned higher for easier access.
Step-by-step
1. Measure the total height of your glasses frame from top to bottom.
2. Find the center of the frame. (For example, if the frame is 40mm tall, the center is 20mm.)
3. Subtract 3mm from the center point.
4. Place the bifocal line at this new measurement. (In the example, the line would be at 17mm from the bottom.)
This is a general guideline for setting the bifocal height that works well for most people.
Ultimately, the placement of your bifocal line should be tailored to what feels most comfortable and functional for you. Some people like to experiment with different heights until they find the perfect balance that suits their daily activities. There’s no universally correct placement—just what works best for your vision and lifestyle. Whether you’re using Flat Top (FT-28) bifocals or Executive Bifocals, the key is to find the setting that allows you to see clearly and comfortably in all the scenarios you encounter daily.
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