Semi Rimless (Eyeglass Frames)

Half of the rim is missing on purpose. The top of each lens sits in a conventional groove. Meanwhile, the bottom is held by a nylon cord roughly 0.5mm thick, strung under tension into a groove ground around the lower edge of the lens. Labs call the whole construction nylor after that cord, and its tension is the only thing keeping the lens from dropping out.

Losing the lower rim loses weight and loses a line. Look down and your eye meets a bare lens edge instead of a bar, which people who read or work at a screen notice inside the first day. Tension is also the failure mode. Nylon stretches with heat and time, so the cord wants replacing every one to two years, before it slackens far enough to release a lens into your bag. Any optical counter stocks the cord and restrings a frame in minutes for very little money. Because a groove cut around the lens edge weakens brittle materials, labs push you toward polycarbonate or Trivex here.

A closed rim holds the entire edge and takes far more abuse in return for grams. Drill mounts remove the top as well and bolt straight through the lens, lighter still and easier to break. Browline frames also load the top of the lens only, but they do it with a thick brow piece over a thin metal lower rim. Browline reads as a deliberate shape while this reads as an absence.

Anyone in progressives does particularly well, since the frame keeps a top rim to align the lens against while leaving the reading zone at the bottom unobstructed. Modest corrections suit it best, since a thick exposed lower edge looks unfinished.

Press gently upward on the lower edge of a lens in the shop. Any movement means that cord has already stretched and the frame is being sold tired. Check that the groove around the lens is centered rather than wandering toward one face of the lens, because an off center groove is where cracks start. Never rest these lens down on a table, since the unprotected lower edge chips before anything else on the frame does.