Ophthalmic Optics and Dispensing

A paraoptometric fields the same three questions from nearly every patient choosing new lenses: what is this lens made of, what shape does it come in, and what extra coatings are worth paying for? Answering well means matching the material, design, and treatment to the patient's prescription, occupation, and budget — in plain language, not manufacturer jargon.

Lens materials trade weight, impact resistance, and optical clarity against each other; no single material wins on every axis. CR-39 plastic is the long-standing baseline: excellent clarity, moderate weight, but it needs an added UV coating and is not impact-rated, so it is a poor choice for children, sports, or safety wear. Polycarbonate largely solves the impact problem — it is roughly ten times tougher than CR-39, lighter, and absorbs UV inherently in the resin itself, which is why it is the default recommendation for kids, monocular patients, and drill-mount (rimless) frames where the lens material must tolerate stress at the mounting holes. Its trade-off is a lower Abbe value, meaning more chromatic aberration (color fringing at the lens edges), especially in stronger prescriptions. Trivex keeps polycarbonate's impact resistance and inherent UV block while improving on its optics, at a similar or slightly lighter weight. High-index materials (1.60, 1.67, 1.74) flatten and thin a lens for strong prescriptions — the higher the index, the thinner the lens for the same power — but Abbe value drops as index rises, so very high-index lenses show the most color fringing of all. Glass is the exception that still occasionally comes up: it offers the best scratch resistance and optical clarity of any option, but it is heavy and, unlike plastic, does not flex under impact — it must be tempered before dispensing so it breaks into small, less hazardous pieces rather than large shards.