81
EW RETINA
retinal pigment epithelium to get
nutrients, such as vitamin A.
"That's what we're measuring—
cholesterol impedes the transport
of vitamin A into the eye. Dark
adaptation speed is knocked down
before visual acuity because it's
directly dependent upon the speed
of the vitamin A cycle. In AMD, that
cycle is impaired very early on," Dr.
Jackson said.
Upward of 70% of patients are
unaware they had AMD until they
already had functional vision loss.
Analyzing the ability of dark adap-
tion may help clinicians identify
these patients before visual loss
occurs.
"By the time clinicians can see
drusen, the macula is fi lled with
cholesterol deposits that are invisi-
ble to today's clinical imaging
methods. Dark adaptation allows
clinicians to detect the pathology
more easily," Dr. Jackson said, liken-
ing the dark adaptation to a cardiac
stress test. In both cases, clinicians
are intentionally stressing the sys-
tem to reveal early stage disease.
"People with early AMD are
the ones primary eyecare providers
want to monitor because you want
to catch them as soon as they con-
vert to late AMD so you can provide
prompt anti-VEGF therapy, which
leads to better patient outcomes,"
Dr. Jackson said.
How it works
The AdaptDx dark adaptometer is
"completely non-invasive" and is
"very similar in form and operation"
to visual fi eld perimeter tests,
MacuLogix notes. Routine tests
take about 5 minutes per eye
(compared to 60 minutes or
more for other devices).
During the test, the retina is
exposed to a bleaching light and the
device then captures how quickly
the retina adapts to darkness.
In a validation study, the
sample consisted of 127 confi rmed
cases of early to advanced AMD
and 21 confi rmed normal cases. The
diagnostic test sensitivity was 90.6%
(P<0.001) and specifi city was 90.5%
(P=0.0271). Agreement between
the fi rst visit and second visit diag-
nosis was high at 94.7%, Dr. Jackson
noted.
"For those with AMD, on
average it took 8 minutes longer to
recover," he said.
For every 1-minute increase
in rod intercept, there was an 11%
increase in odds of having interme-
diate AMD. EW
Editors' note: Dr. Jackson has fi nancial
interests with MacuLogix.
Contact information
Jackson: gjackson@maculogix.com
September 2014
