Nystagmus:
"The Eye Test"
Information
courtesy of Lawrence Taylor - DUIblog
You
may have heard of the "eye test" in DUI investigations.
This is the nystagmus field sobriety test or, more accurately (there
are 47 different kinds of nystagmus), the horizontal gaze nystagmus
test. It is one of the most commonly used field sobriety tests,
as it is one of three which make up the federally-approved "standardized
battery" of tests, or SFSTs.
The
test is essentially a measurement of the movement of the eye. Simply
stated, "nystagmus" refers to a distinctive involuntary
jerking of the eyes; horizontal gaze nystagmus is a pendular (back
and forth) movement. This type of nystagmus is commonly measured
by the officer in three three different ways, each time using an
object such as a pencil, penlight or finger placed a foot or so
in front of the suspect's nose and moving it slowly to the left
and then to the right.
The
first part of the test is to determine the angle of onset of nystagmus
-- that is, the angle at which the moving eye begins the jerking
motion. The suspect looks straight ahead and, without moving his
head, moves his eyes slowly to the right or left. The officer is
supposedly able to detect when the nystagmus begins and is supposedly
able to estimate the angle from straight ahead at the point where
it begins. If the onset is prior to 45 degrees, in theory, the blood
alcohol level will be over .05%.
The
second part of the test is to note whether the jerking becomes more
"distinct" when the eye is moved to the lateral extreme
-- that is, when there is no longer any white of the eye visible
at the outside of the eye.
The
third part is to determine whether there is a lack of smooth pursuit:
rather than following a moving object smoothly from the beginning,
the eye jumps or "tugs".
Under
federal standards, the officer is supposed to use an objective scoring
criteria for each of the three tests, and the total score determines
whether the supect passed or failed.
In
reality, few officers understand the test, administer it
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