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Technical Data
| 1.56 Semi Finished Flat Top Bifocal Lens Blanks | |
Material: 1.56 Index NK55 Resin(Ne=1.549, Abbe=38, Specific Gravity=1.28) Segment Placement: 5mm down -5mm in Add Power: +1.00 to +3.50 in 0.25D steps Segment Size: 28mm |
| CONVEX SURFACE | CONCAVE SURFACE | ||||||||
| Mominal Curve | True Curve | Sag(sagitta: 40mm) | Sag(sagitta: 50mm) | Radius | Radius | CT(mm) | ET(mm) | Dia(mm) | |
| 1.549 | 1.530 | ||||||||
| 4.25 | 4.18 | 4.04 | 1.51 | 2.37 | 131.29 | 132.50 | 8.7 | 11.7 | 70 |
| 6.25 | 6.25 | 6.03 | 2.27 | 3.57 | 87.87 | 88.80 | 11.3 | 8.8 | |
Product Features
----Segment Widths
Bifocal lenses are available with one segment widths: 28 mm. The number after the "CT" in the product name indicates the segment width in millimeters. The diameter 28 mm provides correspondingly wider fields of view.
----Flat Top 28 Bifocal Lenses
A flat top 28 bifocal lens is offers correction for both near and far distances. It is a multifocal lens commonly prescribed for those suffering from both presbyopia and hypermetropia, a condition whereby, with age, the eye exhibits a progressively diminished ability to focus on near and far objects. The flat top lens includes a segment at the lower half of the lens with a prescription for reading (near distance). The width of the flat top 28 bifocal is 28mm wide at the top of the bifocal and looks like the Letter D turned 90 degrees.
Because the flat top bifocal is one of the easiest multifocal lenses to adapt to, it is one of the most popular bifocal lenses in the world. It's distinct "jump" from distance to near vision gives wearers two well-demarcated areas of their glasses to use, depending upon the task at hand. The line is obvious because the change in powers is immediate with the advantage being it gives you the widest reading area without having to look too far down the lens. It is also easy to teach someone how to utilize the bifocal in that you simply use the top for distance and the bottom for reading.
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