defective color vision and was not included in
the sample.

E. Bifocal Displacement. Physical displace-
ment of the spectacle frame by the test item was
quantitatively determined. The subjects wore
zylonite frames selected to fit their facial fea-
tures. A strip of paper tape (1.0 x 35.0 mm)
was placed on each spectacle lens 4.0 mm below
the center of the pupil. After the subject donned
the test item over the spectacles, his head was
positioned in the Frankfort Plane and a fullface
photograph was then taken with a Nikon 35-mm
camera at a distance of 1.0m. Each photograph
was analyzed by measuring the distance from the
center of the pupil to the edge of the tape with
an. optical reticle. The displacement, either up
(+) or down (—) was multiplied by a mag-
nification factor of 7.71 to represent real displace-
ment values.

II. Results.

Mean values of the visual field showed that
the superior field remained normal or only
slightly reduced for all 26 test items. The tem-
poral or Jateral field was also normal when the
subjects wore the one-piece masks or goggles with
transparent side shields. Reduction in the tem-
poral and inferior field with two-piece test items
was caused primarily by the opaque material
surrounding the facepieces of some of the goggles
or by the upper portions of the oxygen masks.
The inferior field was further decreased by those
oxygen masks with prominent nasal cups that
elevated the goggles on the face. The graph of
the mean visual field of test item 08, shown in
Figure 3, is an example of the impairment of
both the temporal and inferior field. One-piece
test items generally provided a larger inferior
field of vision than did the goggles/oxygen mask
combinations. Compensatory head movements
when wearing the test items would tend to en-
large the useful field of vision but may be time
consuming and disruptive to flight-deck duties.

The data of Table 2 indicate that 8 of the 26
test items (30.8 percent) degraded visual acuity
below 20/20 at the 0.4-m distance. Acuity was
somewhat less impaired at 0.76 m (4 of 26 test
items, or 15.4 percent) and at 6.0 m (2 of 26
test items, or 7.6 percent). In all other cases,

TI - 08

Figure 3. Mean values of the visual field for test item

08 (N=5). Broken lines are values with the test

item. Solid lines are values without the test item

(control).

TABLE 2, Visual Acuity
Test Distance
Test tem 6.0 0 0.76 m 0.40 »

OL * - -
02 - LSet 3/5
03 us - Us
04 . Ws 1/5
05 - - 2/5
06 : : .
o7 - - us
08 - - -
09 - -
10 : 2
i - -
12 - - -
re) : 7
4 : : Z
15 .
16 :
ru : : :
18 - 2s
19 : : .
20 : :
a1 : 2
22 : : :
23 SIS S/S 5/5
26 . . .
25 - : -
26 - us 2/5

* ALL test subjects (N= 5) had 20/20 visual acuity,
* Numerator of fraction indicates number of subjects with
less than 20/20 visual acuity.

‘





Ficure 1, Test subject with head positioned in the

Frankfort Plane.

The wear angle of each test item is the angle
between the frontal plane of the head and the
transparent facepiece. This plane was recorded
by marking two points along a plumbline—one
on the upper part and the other on the lower
part of a card attached to the test item, as shown
in Figure 2. The head could then be repositioned
in the Frankfort Plane by realigning the two
points on the card with the plumbline.

Ficure 2, Subject wearing goggles/oxygen mask com-
bination; wear angle is marked by two points on a
card attached to the side of the goggles.

A. Peripheral Field of Vision. Measurements

- were taken on a Ferree-Rand arc perimeter de-

signed to measure the peripheral field 95.0' are
degrees on each side of a central fixation point.
Luminance across the are of the perimeter was
6.45 mL (6.0 fL). The test subject was instructed
to keep his gaze on the central fixation point
while the observer slowly moved a circular white
test target (12 mm in diameter) from the pe-
riphery toward the fixation point and to signal
when he became aware of the moving target.
The peripheral field was measured both with and
without the test items along 12 equally spaced
meridians around the subject’s visual field.

B. Visual Acuity. Tests were conducted at
distances of 6.0 m, 0.76 m, and 0.4 m. The test
symbols were Landolt “C” figures that varied in
size to equate visual acuity levels of 20/40, 20/30,
20/25, and 20/20 at the three distances. The
subject was asked to indicate the position of the
break in the Landolt “C” (either left, right, up,
or down) beginning with the top row of figures
(20/40) and to read from left to right toward
the bottom row (20/20). Measurements were
made at an ambient luminance level of 53.8 mL
(50.0 fl). Incorrect responses were recorded at
each of the three distances. Subjects wearing
bifocal lenses were allowed to look through the
distant portion of the lenses if the bifocal portion
interfered with distant vision.

C. Stereoscopic Depth Perception. Stereopsis
was measured at 6.0 m with the standard
Howard-Dolman apparatus. After donning a
test item, each subject made five rod alignments
by pulling a looped cord attached to a movable
rod to align the rod with a stationary rod. The
final separation between the two rods was read
on a millimeter scale. Each subject, as his own
control, made two series of five alignments with-
out the test items. Ambient luminance was con-
trolled at 53.8 mL (50.0 fL).

D. Color Vision. For test items with tinted
facepieces, Dvorine Pseudo-Isochromatic Plates
were used to detect changes in normal color vi-
sion. A Macbeth easel lamp produced a lumi-
nance of 23.7 mL (22 £L) on the plates. Four
of the subjects read numbers on the 14 test plates
presented in a random sequence, and errors were
recorded. One test subject was found to have


visual acuity was 20/20 (denoted by dashes in
Table 2). The most likely reason for degraded
acuity at the near position (0.4 m) and to some
extent at the intermediate distance (0.76 m) was
the distortion created when the goggles were
pushed upward by the oxygen mask. This dis-
placement caused the subject’s line of sight to
pass through the peripheral, rather than through
the central, portion of the facepiece.

Results of the Howard-Dolham test for depth
perception, shown in Table 3, were calculated in
terms of the percentage of change from control.
Mean values ranged from 2.4 percent for test
item 17 (a goggles/oxygen mask combination) to
404.4 percent for test item 23 (a polyurethane
hood). A close relationship was noted between
test items that created high alignment disparities
and those that degraded visual acuity (compare
test items 02, 03, 04, 05, and 23).

TABLE 3. Depth Perception

Test Mean Alignment Change fron Test —tean Alfgnnent Change Fron
Hees Disparity (om) Gontrol Gees © Disparity (on) Cone¥ol_ (2)
oO 36 6.8 16 21.6 93
oz 428 195.6 1s 19.2 56
os 49.8 268.8 16 19.2 a6
04 20.8 100.6 w 176 26
os 48.5 a9 18 mt 16.7
06 20.2 20.7 9 18.8 22
o ae m6 » a0 48
os a4 95.3 a 2.2 18
0 20.3 19.6 2 18.8 wee
0 23.6 38.7 ry on8 bobs
4 20.9 17.0 » 20.9 86

2 aur 23.8 25 2k 30.5
B 7.2 9.2 2% 36.8 19.2

Results of the color vision evaluation indicated
that the three goggles with tinted facepieces (test
items 06, 09-18) and the tinted fullface hood
(test item 26) caused no alteration in color per-

* ception for the four test subjects with normal
color vision.

Bifocal displacement for the 26 test items is
shown in Table 4. The examples in Figures 4a
and 4b illustrate the finding that bifocal displace-
ment was upward (Figure 4a) with the 21 gog-
gles/oxygen mask combinations (mean +6.62
mm, range +2.20 to +10.38mm) but was con-

TABLE 4, Bifocal Displacement

Mean Displacement Standard Deviation

Test Item cD) (vom)
o1 45.86% 3.63
02 +8.79 3.80
03 49.17 1.60
0% 43.16 6.73
05 42,78 3.29
06 48.40 1.82
07 #2.20 3.18
08 45.94 5.73
09 +10,33 3.64
10 43.16 4.13
i +8.02 4156
12 47,86 5.02
13 48.94 4.32
iu 48.56 3.08
15 43,08 4.85
16 47.40 1,20
7 47,09 5.48
18 48.79 3.38
19 47.25 3.24
20 4,52
aL 5.28
22 1.17
23 3.00
24 5.62
25 8.51
26 212

‘With reference to the center of the pupil (+) indicates
an upward displacement and (-) indicates a dovnvard
displacement,

sistently downward (Figure 4b) when the five
fullface devices were worn (mean —7.66 mm,
range —5.09 to —12.18 mm).

IV. Discussion.

The near-vision portion of an opthalmic lens
should correct visual acuity in the 40.6- to 50.8-cm
(16- to 20-in) range. Bifocal elevations greater
than 2 to 3 mm above the centers of the pupils
(about half the diameter of the normal pupil)
would create a loss of visual acuity in the distant
range (6.0 m) and perhaps also in the inter-
mediate range (0.5 to 1.0 m). To avoid bifocal
interference, the individual must drop his chin
or lean forward and look upward to retain vision
in the distant portion of the lens. However,
this maneuver may not be effective because the
supraorbital ridges limit the superior field of
vision when the head is depressed. The sup-
portive structure surrounding the facepiece of
the test item may limit vision in the same way.
When the tops of the bifocals are elevated about.
6 to 8 mm above the center of the pupils, any
head manuever to see at a distance would be
difficult, if not impossible to perform successfully.


Technical Report Documentation Page

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.
FAA-AM-76- 5
4. Title and Subtitle 5. Report Date

May 1976
VISUAL EVALUATION OF SMOKE-PROTECTIVE DEVICES 6. Performing Organization Code

[8. Performing Organization Report No.

7. Author! s)
John A, Vaughan and Kenneth W, Welsh
9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)
FAA Civil Aeromedical Institute
P.O. Box 25082 11. Contract or Grant No.

Oklahoma City, Oklahoma 73125

13. Type of Report and Period Covered

12. Sponsoring Agency Name and Address
Office of Aviation Medicine

Federal Aviation Administration
800 Independence Avenue, S.W. 14, Sponsoring Agency Code
Washington, D.C. 20591

OAM Report

15. Supplementary Notes

Work was performed under Task AM-B-76-PRS-13.

16. Abstract

This study was designed to determine the visual characteristics of smoke-protective
devices for flight deck crews.

Visual measurements were made on five male subjects, who ranged in age from 35 to
54, while they were wearing each of the 26 devices tested. These measurements
included (1) visual field, (2) visual acuity, (3) stereoscopic depth perception,
(4) color vision, and (5) bifocal displacement,

Reduction in the temporal and inferior fields was found with some of the goggles-
mask combinations, The data indicate that 30.8 percent of the test items degraded
visual acuity below 20/20 at the 0.4-m distance, 15.4 percent at 0.76 m, and 7,6
percent at 6.0 m,. Mean values of depth perception ranged from 2.4 percent to
404.4 percent over control. The three tinted goggles created no alterations in
color perception. Bifocals worn with the oxygen mask were displaced upward; those
worn with the one-piece test items were displaced downward.

Criteria for an a¢ceptable smoke-protective device are discussed.

17. Key Words 18, Distribution Statement
Vision, Smoke protection, Goggles, Document is available to the public through
Oxygen mask the National Technical Information Service,

Springfield, Virginia 22151

19. Security Classif. (of this report) 20. Security Classif. (of this page) TI. No. of Pages | 22, Price
«es $3.00 PC
Unclassified Unclassified “05 MF

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized



Ficure 4a. Photograph of test subject wearing goggles/
oxygen mask combination with spectacles displaced
upward.

Ficure 4b, Photograph of test subject wearing fullface
device with spectacles displaced downward.

Experiments with pilots have demonstrated
that binocular vision is not necessary for pro-
ficient landing performance. Lewis e¢ al.? re-
ported .that monocular occlusion of low-time
pilots during the approach phase has no effect
on landing performance. Landing performance
was measured by the proximity of the touch-
down point to a fixed target on the runway. The
authors confirmed similar results compiled by
Lewis and Krier,’ who studied NASA pilots and
reported no impairment of landing performance
following the sudden loss of binocular vision.
Whether monocular occlusion can be equated to
the alteration in stereopsis caused by the char-
acteristics of the facepiece of a smoke-protective
device is not known.

The data from this evaluation suggest that an
acceptable smoke-protective device should:

1, Create no impairment in distant or near
visual acuity when worn by a normal-sighted
presbyopic individual wearing bifocal lenses.

2, Allow minimal reduction in the wearer’s
peripheral field of vision. The device should pro-
vide a peripheral vision envelope of at least 120°
(60° on each side of the central point) in the
horizontal meridian, and 80° (40° above and be-
low the central point) in the vertical meridian.

3. Create no significant stress and/or change
in the integrity of the binocular system. Sig-
nificant alterations include diplopia, suppression
of vision in one eye, or a marked degradation of
stereoscopic depth perception.

4, Cause no changes in color perception, in-
cluding the addition of color to a neutral surface
(white or gray) by a tinted facepiece or the re-
duction in normal color perception by selective
absorption.

5. Be designed and constructed to fit snugly
but also allow adequate space for corrective
lenses to be worn without being displaced up-
ward or downward when used in combination
with an oxygen mask.

REFERENCES

1, Harper, C. R.: Physical Defects of Civilian Pilots
Related to Aircraft Accidents, AEROSPACE MED.,
35 :851-856, 1964,

2. Lewis, C. E., Jr, W. R. Blakely, R. Swaroop, R. L.
Masters, and T. C. McMurty: Landing Performance
by Low-Time Private Pilots After the Sudden Loss of

Binocular Vision-Cyclops II, AEROSPACE MED.,
44 :1241-1245, 1973.

3. Lewis, C. E., Jr, and G. E. Krier: Flight Research
Program: XIV. Landing Performance in Jet Aircraft
After the Loss of Binocular Vision, AEROSPACE
MED., 40 :957-962, 1969.

23785





VISUAL EVALUATION OF SMOKE-PROTECTIVE DEVICES

I. Introduction.

Federal Aviation Regulations, Part 25.1439 b 4,
state that protective eye equipment may not cause
any appreciable adverse effect on vision and must
allow for corrective lenses to be worn. A report
by Harper indicates that pilots with defective
visual and oculomotor functions (excluding de-
fective distant visual acuity that has been cor-
rected by lenses) have a higher incidence of
accidents than those with unimpaired vision.
However, until aircraft accidents can be posi-
tively correlated with specific visual deficiencies,
all of the visual functions evaluated in this study
should be considered equally significant. The
possibility exists that smoke-protective face masks
might degrade vision to the point that safety is
compromised. This investigation was designed
to test the visual properties of such devices.

Il. Materials and Methods.

Visual performance was evaluated for the 26
test items shown in Table 1. These test items
were selected because they passed or indicated

TABLE 1, Test Leems

Test. Leon goggle Respirator
a Sierra 322-01 Puriean 114120-01
02 Sierra 322-01 Sierra 358-1030
03 Sierra 322-01 Skerea 358-1002
0% Sierra 322-01 Sierra 232-37
05 Sierra 322-20 Sierra 520-120
06 Puritan 118071 Puritan 116020-20
07 Robertshaw 595-900 Puritan 2401-36
08 Robertshaw 595-900 Puritan 114020-20
09 American Allsafe 6202-138 Sierra 358-1030
10 Aperican Allsafe 6202-13R Sierra 520,120

Bouton 1970 Puritan 114020-20
Purican 114120-01
Sterra 358-1030
Sierra 358-1002
Sterra 358-62
Sierra 20-120
Sterea 232-37

Eros scoct intertech

Puritan 114020-20
Sierra 520-120

. Sierra 520-120
2 Robertshaw 900-002-066

23 Robertshaw 900-700-062-01
2% Seott 10200c2A

25 Sierra 651-100-1

26 Robertshaw 900-700-062-02

the potential to pass minimum acceptable level
of gas protection as determined by investigators
in the Protection and Survival Laboratory at the
FAA Civil Aeromedical Institute. The 26 items
consisted of five fullface (one-piece) and eight
combination (goggles and oxygen mask) units.
Five of the eight goggles were tested with two
or more oxygen masks,

The five male test subjects who participated in
the study ranged in age from 35 to 54 years
(mean 43.2 years). Three had uncorrected visual
acuity of 20/20 or better at 6.0 m, 0.76 m, and
0.4 m, and the remaining two subjects wore cor-
rective lenses to attain these acuity levels. Either
nonprescription or corrective lenses were worn
with each test item by each subject throughout
the experiment with the exception of the visual
field measurements.

To minimize experimental variability, all the
tests were conducted with the subject’s head in
the Frankfort Plane, a standard reference plane
for head position. It is defined as the position
of the head when the upper border of the audi-
tory meatus is horizontally aligned with the
lowest point on the orbital margin of the maxil-
lary bone. The device for positioning the head
in the Frankfort Plane is shown by Figure 1.
It consists of a metal ear bar inserted about 1.5
cm into the auditory meatus and adjusted to ap-
ply slight pressure on the upper surface of the
ear canal. A curved bar in a horizontal plane
with the ear bar is swiveled forward to touch
the lower orbital margin of the maxillary bone.
The pitch of the head was pivoted around the
ear bar by an adjustable chinrest to align the
tip of the curved bar with the lower orbital
margin. The chinrest together with two cupped,
adjustable occipital supports, formed a rigid
3-point craniostat.