Download Effects of Alcohol on Visual Accommodation and Eye Movement

Effects of Alcohol on Visual
Accommodation and
Eye Movement Latency
J. Levett1, L. Karras, and G. Hoeft
It is generally agreed that the ingestion of ethyl alcohol dulls the physiological and
mental responses of the human body, that is, alcohol affects the central nervous
system and the peripheral nervous system of the body (2). This diminution of
responses is caused by alcohol’s capacity to impair the impulse conduction and trans­
mission in excitable cells of the nervous system (13). Based on the above evidence, two
components of the visual system, accommodation and horizontal saccadic eye move­
ment, were examined, using several subjects with various blood alcohol concentrations.
In order for vision to be clear, a sharp image must fall upon the retina. This is
accomplished by a feedback control system in the accommodation process. In driving,
as in reading, the predominant eye movement is the horizontal saccade (10). If the
response time of both the eye movement and accommodation is affected by alcohol
then it may be postulated that serious consequences can result while driving under the
influence of alcohol. The intention of this study was to examine the effects of alcohol
on these visual tasks and to discuss what influence this alcohol-impaired vision has in
the driving situation.
METHODS AND PROCEDURE
The apparatus used to measure the monocular accommodation response time was the
triple-function ocular monitor described in (9) which uses infrared techniques. Visual
cues instructed the subject to accommodate two diopters from a far target to a near
target and conversely, from a near target to a far target. The far target was 20 feet
from the eye and the near target was 18 inches from the eye. The visual cue was
recorded on a time reference axis, thus providing a time reference of applied
accommodation stimulus in which to measure the accommodation response time of
the lens. The subsequent lens accommodation from the far target to the near target
will be referred to as positive accommodation, and conversely the lens accommodation
from the near target to the far target will be referred to as negative accommodation.
The accommodation parameters that were specifically measured are the latency
response time and the total accommodation time. The latency response time is the
time necessary for the lens of the eye to start to accommodate after the accommoda1Department of Biomedical Engineering, Rush-Presbyterian-St. Luke’s Medical Centre, 1753 West
Congress Parkway, Chicago, Illinois, 60612, U.S.A.
305
306
J. Levett, L. Karras, et al.
tion stimulus had been applied. Total accommodation time is the time needed for the
lens to accommodate fully after the application of the accommodation stimulus.
Accommodation parameters with and without alcohol influence were measured in a
darkened environment. No food was taken three hours prior to the experiment and no
food was allowed during the experiment. The subject was then given an alcoholic
beverage to drink at his own rate for one hour. A rest period of one hour followed the
drinking hour. The rest period was necessary to insure collection of data during the
body’s alcohol elimination phase. In this phase, subjects would maintain a level of
blood alcohol long enough to collect data, since the alcohol elimination rate is 15
mg/100 ml/hour (13). The absorption phase has an alcohol uptake rate of approxi­
mately 15 mg/100 ml/5 minutes (8) under the fasting conditions of this experiment.
This absorption rate would make collection of accommodation data for a blood
alcohol level during the absorption phase impossible. All data for each subject were
collected in one session. After the rest period the blood level was obtained by analyz­
ing a sample of the subject’s alveolar air with an instrument that correlated breath
alcohol level with the actual blood alcohol concentration. The instrument used to
make this correlation was an Intoxilyzer (6, 7). Twenty-five positive accommodations
and 25 negative accommodations were obtained from each of three subjects prior to
ingestion of alcohol. The average of these negative and positive accommodation
response times was used as a control. Twenty-five negative and positive accommoda­
tion response times were subsequently measured for each determined blood alcohol
concentration of the subject. The range of blood alcohol concentrations for the
accommodation experiments was from 50 to 100 mg/100 ml. The average of these
negative and positive responses was determined for each measured blood alcohol con­
centration and compared with the controls.
In the measurement of eye movement latency, a projector constructed from a
low-power helium-neon laser was used to display a stimulus. The laser projected a spot
of red light of about 1/4-inch diameter on a white wall from a distance of three feet.
This projected spot served as the initial fixation point of the step stimulus. In order to
produce a step input to the subject the laser beam was interrupted by a mirror
attached to a relay and reflected to a second mirror attached to a modified meter
movement which was used as a mirror galvanometer. The reflection of the laser beam
from the mirror galvanometer served as the second fixation point of the step input.
The amplitude of the step stimulus target movement was controlled by the mirror
galvanometer. The horizontal movement of the target was one foot in this experiment.
An eye movement detector was constructed from a pair of eyeglass frames and
photo transistors (11). A small infrared light source also mounted on the eyeglass
frame was used to illuminate the iris. Eye movement would then be detected when the
differential voltage between the photo transistors varied.
Subjects were seated on an ophthalmic examination chair ten feet from a white
wall where the stimulus target was located. The one-foot movement of the stimulus
dot induced a horizontal-tracking saccadic eye movement of about six degrees. The
saccade was then detected by the eye movement detector and processed on-line by a
Model 7100 Nuclear-Chicago data retrieval computer which had been triggered by the
onset of the stimulus. The computer was operated in the time histogram mode. In this
mode of operation a time base record of the occurrence of a saccadic eye movement
was made in the form of a histogram for each blood alcohol level. Several eye move­
ment histograms consisting of 25 responses each were completed and used as controls.
All eye movement latency measurements were made in a darkened environment.
After the controls were obtained, the subject, who had been fasting for at least
Eye Movement and Accommodation
307
three hours, was then asked to drink a quantity of 190-proof ethyl alcohol mixed with
an equal volume of lime juice. The amount of alcohol given to the subject was usually
enough to obtain a blood alcohol concentration of 100 mg/100 ml. The subject was
asked to drink the grain alcohol mixture in as short a time as possible (less than ten
minutes). The time at which the drink was finished was defined as the elapsed time T =
0. At T = 15 minutes, a breath test was taken on the Intoxilyzer (6, 7) to determine
the blood alcohol level. Within two minutes after the breath test an eye movement
histogram of 25 responses was made. Breath tests and eye movement histograms were
made every 15 minutes for a period of three to four hours. Blood alcohol concentra­
tions for the eye movement latency ranged from 30 to 140 mg/100 ml. The histograms
of eye movement latency consisted of responses elicited from 25 stimuli. Average
control (no blood alcohol level) eye movement latency was then compared with
average eye movement latency at different levels of blood alcohol concentration.
It should be noted that visual accommodation and eye movement latency experi­
ments were not conducted concurrently and in each experiment subjects were allowed
to dark-adapt for 30 minutes.
RESULTS AND DISCUSSION
The results of the monocular accommodation experiments for two diopters of
accommodation for each subject at various blood alcohol levels are given in Table I
and Figure I.
TABLE I
Tabulated Results o f Accommodation
Parameters Affected by Alcohol
Subject MPM
Subject FKP
Subject PF
30_______
Age 21
Age
33______________________ Age
BAC
Negative
Positive
Negative
Positive
Negative
Positive
(m g/100m l) A ccom m odate A ccom m odate A ccom m odate A ccom m odate A ccom m odate A ccom m odate
A
B
B
A
B
A
B
A
B
B
A
A
.41 1.02
.89
.40 1.00
.39
.38
.93
.90
CONTROL .38
.38
.91
.50 1.18
.44 1.12
.53 1.15
.45 1.10
.45
1.00
50
.46 1.04
.53 1.14
.51 1.16
.42 1.08
.45 1.15
.49 1.01
60
.50 1.03
.52 1.20
.55 1.13
.50 1.20
.45 1.10
.49 1.00
.49 1.05
70
.47 1.22
.44 1.15
.50 1.03
.52 1.12
80
—
.47
1.06
.53 1.16
90
—
—
.49 1.13
1.30
.51
100
-
A = L atency R esponse Tim e (SEC)
B = T otal A ccom m odation Tim e (SEC)
The numerical results in Table I are averages of 25 samples for the particular
blood alcohol level and mode of accommodation listed. The deviation around these
averages was ± 1 0 per cent. The average value of the latencies obtained in this experi­
ment for both the negative and positive accommodation controls corresponds closely
to the results obtained by Campbell and Westheimer (3). They found that for a step
function stimulus, latency for positive and negative accommodation was .38 seconds
and .36 seconds respectively.
308
J. Levett, L. Karras, et al.
O
W
TOTAL
ACCOMMODATION
w 1.4
CO
* I3
UJ
IUJ
1.2<
tt:
^ !• . I'
Q_
1.0
c o n t r o l A = 0.95 s e c
c ontrol A =0.9 4 s e c
o< •9 0
O
5 ,8 0 -
positive a c c o m m o d a t io n
negative a c c o m m o d a tio n
oo
S .70
Ll.
°
,6 0 -
LATENCY
UJ
? .50-
»-
contro l #=0,39 s e c
c ontrol o = o . 3 9 s e c
,40
~ r~
50
60
~!— ~~T~ ~T~
70
80
90
l
100
BLOOD ALCOHOL L E V E L
^mg/100 ml)
Figure 1
Average latency and total accommodation response times o f all subjects indicated in
Table 1 as a function o f blood alcohol levels.
It has been suggested that the time required for positive accommodation may be
increased by 0.10 to 0.20 seconds for blood alcohol concentrations of 60 mg/100 ml
(2). The data in Table I show that both positive and negative total accommodations of
two diopters are retarded for ranges of blood alcohol levels of 50 mg of ethanol/100
ml of blood to 100 mg/100 ml by 0.10 to 0.39 seconds. Latency response time in this
range was retarded by .04 to .15 seconds. In general, the accommodation responses
under the influence of alcohol are slower than the controls by a factor of 10-40 per
cent. Figure 1 indicates that the degree of retardation of the accommodation process
increases as a function of the blood alcohol concentration.
In a neurological sense, accommodation is controlled by both the parasympa­
thetic and sympathetic divisions of the autonomic nervous system (4,12). Stimulation
of the sympathetic division and inhibition of the parasympathetic will induce negative
Eye Movement and Accommodation
309
accommodation; and likewise, stimulation of the parasympathetic division and inhibi­
tion of the sympathetic division will induce positive accommodation. Table I shows
that two of the subjects’ negative accommodation was more affected by alcohol than
positive accommodation. The converse is true for the third subject. One could only
conclude from this the need for further study to determine what (if any) differential
effects alcohol has on the neurological control division of the accommodation process.
A limiting factor in the accommodation experiments has been the observance of
alcohol gaze nystagmus (AGN). Aschan (1) observed that the average blood alcohol
level of individuals developing AGN was 60 mg/100 ml and that the threshold range
for developing AGN was 30 mg/100 ml to 90 mg/100 ml. He also found AGN to be
intensified in a monocular situation. It has been observed in our experiments that two
of our subjects developed AGN when their blood alcohol reached levels of 100 mg/100
ml. The data then contained an amplitude of AGN which swamped the accommoda­
tion signal completely and further measurement was not attempted. Thus, it appears
that a blood alcohol level sufficient to trigger AGN constitutes a threshold beyond
which successful experimentation is no longer possible.
Figure 2 shows the elapsed-time-based plot of the mean saccadic eye movement
latency values (of five subjects) with the associated ± 95 per cent confidence limits of
the plotted mean value. Also indicated on the plots are the corresponding blood
alcohol levels determined by breath analysis. The latency data point at N (indicated on
the time axis) is the normal non-alcohol mean latency of the subject. The first few
data points on the plots have no associated blood alcohol values because a minimum of
15 minutes must pass after ingesting alcohol before a breath sample can be taken,
otherwise high blood alcohol readings will result due to residual alcohol in the mouth.
It should be noted that AGN did not dominate the eye movement data when it occurred.
As shown in Table II, the overall mean value for the control responses was .248
seconds with an upper 95 per cent confidence limit of .262 seconds and a lower 95 per
cent confidence limit of .234 seconds. The mean value of eye movement latencies that
occurred at the maximum blood alcohol levels was .314 seconds. When compared with
the mean normal value (.248 seconds) a 26 per cent increase in latency is seen.
Summary of Experimental Data and Results Pertaining to Eye Movement
Latency.
TABLE II
Subject WHT
(Lbs)
DB
GG
TS
LK
MB
Average
Avg. w/
Normal
Study
115
140
170
170
160
—
-
Maximum BAC
AVG
MAX Latency Laten Elapsed
Quant
190 PF Normal BAC (Sec) INCR Time
Alcohol Latency (mg/
(%) (Min)
(Sec) 100ml)
(Oz)
20
60
100
.340
2
.283
42
120
.324
140
.228
2.5
.244
3
90
110
.236
3
30
30
.406
130
.313
3
.304
15
60
120
.265
3
21
.314
70
108
.259
-
.248
-
.314
26
-
Maximum Latency
Max BAC Laten Elapsed
Laten (mg / INCR Time
(Sec) 100ml) (%) (Min)
.379
.339
.285
.406
.321
.333
.333
90
130
60
130
110
95
-
34
48
20
30
21
28
34
90
105
15
30
45
57
-
310
J. Levett, L. Karras, et al.
MINUTES
Figure 2
Composite o f five recording sessions (Table II) showing the mean eye movement
latency values and blood alcohol levels by elapsed time.
The maximum latency increase occurred, in most cases, at elapsed times dif­
ferent from those associated with maximum blood alcohol levels. When the average
maximum latency (.333 seconds) is compared with the mean normal value (.248
seconds) a 34 per cent increase in the horizontal eye movement latency is seen.
Although the eye movement latency increased with the ingestion of alcohol, it
appears that eye movement latency does not increase proportionally with the blood
alcohol concentration except during the absorption phase of alcohol. Table II and
Figure 2 clearly indicate this and suggest that perhaps there is a saturation threshold of
blood alcohol concentration above which eye movement latency is the same. Further
studies are needed to determine if such a saturation threshold exists. Figure 2 indicates
that eye movement latency reaches a saturation level in the range of 80 to 100 mg/100
ml. Because the principle eye movement made in the operation of a motor vehicle is
the horizontal saccade (10) and because the system of accommodation is responsible
for a clear image on the retina, the ability to drive safely is seriously compromised by
the use of beverage alcohol, according to these data.
Studies have been conducted to determine how much time the visual task
components (eye movements and accommodation) require in order to shift one’s sight
from a far point such as the road to the dash board and back to the far point (5).
These studies showed that positive and negative accommodation required the greater
part (40%) of the driver’s time (.5 seconds to .8 seconds) when shifting sight from the
highway to the dashboard to the highway, whereas the eye movement task required
about 225 msec or about 15% of the sight-shifting task. Results from our experiments
showed an increased eye movement latency up to 100 msec and an increased
accommodation response time up to 400 msec at the 100 mg/100 ml blood alcohol
Eye Movement and Accommodation
311
concentration in a darkened environment. This would lengthen the round-trip time of
eye movement and accommodation when shifting vision from far to near to far by a
full second, meaning that the driver would travel (at 60 mph) an extra 88 feet, in
addition to the normal 176 feet, without a clear and concentrated view of the road.
Needless to say, effects of alcohol on the visual system, along with the effects of
alcohol on the muscular response time and personal psychology at high velocities of
travel become crucial to highway safety, especially when ambient highway and
weather conditions greatly reduce visibility. These results are of particular interest
when it is considered that 30,000 vehicular deaths per year are alcohol-related.
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