Most of the new direct ophthalmoscopes and BIOs come equipped with a switch that makes the light green, or “red-free.” These filters are handy due to the fact that red-free light is absorbed by the RPE, creating increased contrast during your exam (see pic on right).
Here are a few times when the red-free filter can help you during your exam:
Increased vessel detail: red-free light gives a better contrast between retinal vessels and the underlying background. The retinal vessels, and other blood on the retina, will look black, so that subtle changes (e.g., small hemes, ill-defined exudates, etc.) will stand out more.
Assessing depth of pigmented lesions: retinal lesions will look black and choroidal lesions will either disappear or become dimmer/gray.
Detecting early losses of the NFL: handy for suspected glaucoma or optic nerve disease because the red-free light bounces off the NFL, making it easier to see; loss of the usual “stripey” look to the NFL with the red-free filter could indicate nerve fiber loss.
Good for light sensitive patients: decreases the intensity of the light while still enhancing retinal details.