Flat-Top (D-Seg) Bifocal Lenses

Product Introduction

Classic Precision: The Engineering of Flat-Top Bifocal Geometry

Flat-top bifocals, often referred to as D-Seg lenses due to the "D" shaped near-vision segment, remain one of the most reliable solutions for presbyopic patients who require distinct, non-overlapping visual zones. The optical architecture of a flat-top lens is designed to provide a wide, stable area for reading while maintaining a clear, expansive upper zone for distance vision. The defining characteristic is the straight horizontal line at the top of the segment, which is strategically positioned to minimize the "image jump" effect—a common phenomenon in older bifocal designs where objects seem to shift position as the eye moves across the segment boundary. Our D-Seg lenses are produced using high-precision liquid casting technology, ensuring that the transition between the distance carrier and the reading add is structurally seamless and optically stable. Available in various segment widths, most notably the 28mm standard, these lenses offer an optimized field of view that caters to the natural scanning motion of the human eye. By utilizing high-purity resins, we ensure that the chromatic aberration within the reading segment is kept to an absolute minimum, allowing for crisp, high-contrast text rendering. This design is particularly favored by experienced bifocal wearers and individuals whose occupations involve frequent switching between distant objects and close-up documents, providing a level of categorical clarity that progressive lenses sometimes lack.