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Optical Sensor to Monitor Pupillary Light Reex 559
contraction interval (2/3CI), which is the time for which
the amplitude reaches 1/3 of the contraction phase value,
1/3 redilatation interval (1/3RI), which represents the
time for which the amplitude reaches 1/3 of the redilatation
phase value, and nally amplitude (A), which represents
the dierence between the maximum and minimum
values of the diameter.
2. Description of the experimental model
and the test stand
Design of the sensor for measuring PLR and PST as
well parameters of the eyelid covering the eyeball were
preceded by laboratory tests. The purpose of the research
was to verify the possibility of identication of
time-varying PLR behavior in relation to the PUI factor
described in the literature. At the same time, the requirements
for the designed optical sensor were collected. The
resolution of the converter, frequency of image acquisition
and required speed of the pupil detection algorithm
were taken into account.
The study was conducted in two stages. The rst step
was research where assumptions were veried. The second
stage consisted of a study of the designed PLR sensor.
The rst phase of the study was preceded with a
series of experimental research of the commercially available
F 2 D Fit-For-Duty device by AMTech. The experimental
model assumed verication of PLR parameter
usability in correlation with results of the pupillography
sleepiness test PST. Research was performed on a group
of 10 volunteers in a laboratory environment during at
night. The average age of participants was 34.8 ± 6.5
years. Each participant was familiarized with the description
of the experiment and agreed to participate in
the study. The PLR measurements were taken on both
eyeballs, which were exposed to a series of ve ashes
with the interval of 30 s. The second phase of the experiment
involved testing the constructed PLR sensor.
Functional tests were also carried out on a group of 10
volunteers. The study took place in an ophthalmology
darkroom, which provided necessary conditions for testing.
Measurements were performed in the identical measurement
workow, as in the case of pilot studies [13].
3. Test results
Initial results showed high usability of the dedicated
parameters characteristic for the PLR in estimating the
level of fatigue and lowered concentration, as well as
high correlation with the PUI index (Table I). Statistical
analysis was performed using conventional statistical
methods based on variance analysis. They were multi-
-dimensional, multi-factor analyses of identiable variables
from the pupillary reex signal, categorized by Person,
Task, Eye variables and the light excitation sequence
(Prole). In the subsequent measurement times, parameters
were estimated that described the relative amplitude
and contraction velocity of the pupillary reex (Table II).
Measurements for each person were made four times with
the average interval of 2 h between hours 11.00 PM and
6.30 AM. These changes proved to be statistically significant.
Investigations shown that the dierence between the
rst and last measurement point is 3.07%. With the average
value of the observed changes in pupil width of
1.77 mm, the required measurement accuracy could not
be less than 0.09 mm. This value is necessary to design
the sensor in order to observe the changes in the work
of the ANS for the experimental model adopted. It was
necessary to analyze the behavior of the contraction velocity
parameter in order to determine the required speed
of the optical system. The scope of averaged parameter
values for the rst and last measurement was 0.5 mm/s.
It means that the measurement resolution cannot be less
than 0.25 mm/s. These assumptions were adopted in the
design of the PLR optical sensor.
TABLE I
Table showing the values of the rPUI and rPUI rel parameters
in successive measurement points.
rPUI
rPUI rel
task N mean st.d. mean st.d.
All 398 0.83 0.42 0.20 0.29
0 99 0.62 0.25 0.00 0.00
1 102 0.76 0.35 0.13 0.15
2 98 0.91 0.40 0.28 0.17
3 99 1.02 0.55 0.39 0.45
TABLE II
Table showing the values of the relative amplitude
and contraction velocity indicators in successive
measurement points.
Rel. amplitude Contr. velocity
Task N mean st.d. mean st.d.
0 79 24.21 5.11 3.98 0.82
1 76 25.53 5.28 4.21 0.89
2 80 26.22 5.36 4.29 0.83
3 79 27.28 5.47 4.49 0.87
4. Optical sensor to monitor pupillary
light reex
In pupillary light reex testing, it is most important
to determine the parameters of pupil response to light
stimulation with a specic duration (t = 250 ms). The
measurement method for PLR determines the design of
the illuminator control system, image acquisition system
and software. In the adopted implementation the change
of pupil size in time is determined by analyzing the motion
camera image. The acquired image is recorded in the
near-infrared band (λ = 850 nm) by the Optitrack V120
camera. The red KPTD-3216SURC LED with the wavelength
of λ = 640 nm was used as an excitation source.