red-free filter

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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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 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