red-free filter

Gynecology A green or blue filter used in colposcopy, which ↑ contrast between blood vessels and background, improving evaluation of superficial vessels. See Colposcopy.

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References in periodicals archive ?

This machine has an ultra-widefield lens, alongside a red-free filter, which means that more of the peripheral part of the fundus can be seen.

The Oculus Pentacam and the Daytona: newly qualified optometrist, Krupa Mistry, reveals the two data-collecting tools that she couldn't be without in hospital practice

* The red-free filter (green light) can be used to visually enhance lost nerve fibre bundles in glaucoma, or to give greater contrast to haemorrhages and the retinal vasculature

Volk lenses: optometrist Alan Hawrami discusses the importance of Volk lenses in everyday practice

Choroidal naevus: Mildly elevated lesion with a feathery margin and consistent pigmentation, which disappears with a red-free filter