Welch Allyn 118 Series PanOptic Ophthalmoscope - User Manual - Manual (Page 17)

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used to help distinguish veins from arteries; veins stay relatively
blue, but oxygenated arterial blood makes arteries appear blacker.
This greater contrast makes differentiation easier for the
examiner.
6. Cobalt Blue Filter (Model 11820 only): In conjunction
with fluorescein dye applied topically to the cornea and an
add-on magnifying lens (included), this filter is helpful in
detecting corneal abrasions and foreign bodies. In this
way, it can be used as a surrogate to a Woods Light.
7. Half-Moon Aperture (11810 Only): Provides a
combination of depth perception and field-of view.