Redfree

Redfree, or red-free, is a term used in ophthalmology and optometry to describe imaging and examination techniques that employ a green filter or green-spectrum illumination to suppress red tones in retinal images and viewing. The goal is to increase contrast and highlight superficial retinal structures, particularly the retinal vasculature and nerve fiber layer, as well as certain lesions.

Mechanism and method: Red-free imaging typically uses green light around 500–570 nm or a green filter during fundus photography or direct/indirect ophthalmoscopy. Because hemoglobin absorbs green light, blood vessels and hemorrhages appear darker against a lighter background, while choroidal and deeper tissues are relatively subdued. This monochrome view reduces color variability and can reveal pathology that may be less conspicuous on color images.

Clinical uses and usefulness: Red-free imaging is commonly used to assess retinal vessels, microhemorrhages, cotton-wool spots, and nerve fiber layer defects, and to aid in glaucoma surveillance, diabetic retinopathy evaluation, and hypertensive retinopathy. It is often acquired alongside color fundus photographs to provide complementary information, but is not a substitute for other imaging modalities such as OCT or fluorescein angiography.

Availability and interpretation: Most modern fundus cameras and ophthalmoscopes offer a red-free mode as a standard feature. The technique is simple, inexpensive, and noninvasive, but its findings should be interpreted within the broader clinical context.