Welch Allyn 11720 Guide D'utilisation page 4

Red-free filter: When the switch is positioned to the left (while
facing the instrument front) it will be beneath a green dot and the
red-free filter will be in place. This can be used in conjunction with
any aperture. The red-free filter excludes red rays from the
examination field; this is superior to ordinary light in viewing slight
alterations in vessels, minute retinal hemorrhages, ill-defined
exudates and obscure changes in the macula. The nerve fibers
become visible and the observer may note the disappearance of
such fibers, as in optic nerve atrophy. The background appears gray,
the disc appears white, the macula appears yellow, the fundus reflex
is intense and the vessels appear almost black. This filter is also
used to help distinguish veins from arteries...veins stay relatively
blue, but oxygenated arterial blood makes arteries appear blacker.
This makes differentiation easier for the examiner.
Crossed linear polarizing filter: When the switch is positioned to
the right (while facing the instrument front) it will be beneath a while
circle with crosshairs inside. The crossed linear polarizing filter will
be in place. This filter is used to eliminate corneal glare and
reflection and can be used with any aperture. For more information
on this filter turn to page 9.
Additional uses for the ophthalmoscope
In addition to examination of the fundus, the
ophthalmoscope is a useful diagnostic aid in studying other
ocular structures. The light beam can be used to illuminate
the cornea and the iris for detecting foreign bodies in the
cornea and irregularities of
the pupil. By placing the +15.00 lens in the scope and
looking at the pupil as in fundus examination
[2 inches (5cm) distance from patient], the
physician may verify doubtful pupillary action.
The practitioner can also easily detect lens opacities by
looking at the pupil through the +6 lens setting at a distance
of 6 inches (15cm) from the patient. In the same manner,
vitreous opacities can be detected by having the patient look
up and down, to the right and to the left. Any vitreous
opacities will be seen moving across the pupillary area as
the eye changes position or comes back to the primary
position.
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