F-BAM is primarily a
glare tester, however, due to the lighting parameters,
macular photostress
and the
entoptic phenomenon of flying corpuscles can be tested.
The diffuse lighting
for the Flood BAM is similar in principle to the
hand-held Brightness Acuity Test (BAT)1
manufactured by
MARCO Ophthalmic, Inc..
Flood lighting mimics bright outdoors lighting
and light diffusion through a picture window.
The F-BAM provides an
alternative to the BAT for those clinicians
accustomed to diffuse background glare testing.
Like the BAT, the F-BAM has three levels of
background illumination in a hemispheric bowl that is
held close to the eye.
As a result, one possible source of error is
pupil constriction by the illuminator; certain patients
with cataract perform better with pupil constriction,
thereby giving a false-negative test2.
Conversely, the third level (brightest) is
dazzling, inducing false-positive results2
.
1.
Holliday, Trujillo, & Ruiz. Brightness Acuity
Meter (BAT) and outdoor visual acuity in cataract
patients. J Cataract and Refractive Surgery, Jan 1987,
67-69.
2.
Atlas of Cataract Surgery, Chap. 1, p2 by Samuel
Masket.
MACULAR
PHOTOSTRESS TESTS (F-BAM)
The
brightness of the F-BAM provides for macular
photostress testing when brightness is set on
high and
the bowl port is occluded. The BAM™ serves as
saturating light source.
After light exposure of the macula there
is a normal delay period for visual recovery.
In certain diseases2 of
the macula the refractory period is prolonged.
Blocking the optical portal of the glare
bowl changes the glare bowl into a photostress
enclosure.
With the plug in place, viewing
brightness is ~600 Ft. Lamberts.
Entoptic Flying Corpuscles Phenomenon (F-BAM)
.
The blue-field entoptic phenomenon can be seen best by having the subject
look into light with a narrow optical
spectrum centered at a wavelength of 430
nm. Under such conditions, bright
corpuscles are observed flying around
the subject’s fovea. Most likely, this
phenomenon is caused by the fact that
red, but not white, blood cells absorb
short-wavelength
light.
Leukocyte movement underlies the
blue-field entoptic phenomenon3.
This entoptic phenomenon has been
shown to predict macular function in
eyes with vitreous hemorrhage4 and
cataract5.
The LED bulb of the BAM™ has a peak near 440 nm and
explains the prominence of this
phenomenon
while
viewing the BAM™.


