United States Army School of Aviation Medicine

Fort Rucker, Alabama

MARCH 1999

STUDENT HANDOUT

TITLE: NIGHT VISION ORIENTATION

FILE NUMBER: 2/9/9E/UEA/UEB/UEE/5/31/4501-1

PROPONENT FOR THIS LESSON IS:

United States Army School of Aviation Medicine

ATTN.: MCCS-HAF

Fort Rucker, Alabama 36362-5000

FOREIGN DISCLOSURE RESTRICTIONS: The materials contained in this lesson plan (LP) have been reviewed by the instructor/training developer and determined to be public domain materials. This product is releasable to military students from all requesting foreign countries without restrictions.
 
 

MARCH 99

At the completion of this lesson the student will:

A. ENABLING LEARNING OBJECTIVE (ELO) #1:

a. The cornea is the transparent protective tissue located over the front of the eye. It is almost circular in shape and projects forward. The degree of curvature varies with different individuals.

b. The iris is the round pigmented (colored) membrane surrounding the pupil, having ciliary muscles that adjust the size of the pupil to regulate the amount of light entering the eye.

c. The pupil is the opening in the center of the iris (black centerportion). It allows light to enter the eye. During daylight conditions the pupil constricts, during dark conditions the pupil dilates.

d. The lens is a transparent, biconvex membrane located behind the pupil. The lens directs light rays entering the pupil upon the retina. The retina is a thin multi-layered membrane which covers most of theposterior compartment of the eye. The retina contains the rod and cone cells of the eye. These cells permit us to see. The retina also contains a coloring tint called rhodopsin or visual purple which aids in the effectiveness of the rods during low light conditions. When exposed to sunlight, the retina cells become bleached resulting in a temporary decrease in night vision.

B. ENABLING LEARNING OBJECTIVE (ELO) #2:

a. Astigmatism is caused by an unequal curvature of the cornea resulting in the inability of the eye to focus on multiple meridians simultaneously such as vertical and horizontal objects.

EXAMPLE: Being able to focus on telephone poles and towers (vertical) but not the telephone wires (horizontal) or vice versa.

b. Myopia (nearsightedness) is a condition caused by a refractive error in the lens which focuses distant objects in front of the retinal plane.

c. Hyperopia (farsightedness) is a condition caused by a refractive error in the lens which focuses near objects behind the retinal plane.

d. Presbyopia occurs when the natural aging process affects the human eye causing the lens to harden and lose its elasticity resulting in the inability of the eye to focus on near objects.

C. ENABLING LEARNING OBJECTIVE (ELO) #3:

a. Radial keratotomy is a operation in which a series of incisions are made upon the cornea from its outer edge towards its center in a spoke like fashion. Performed to flatten the cornea and thus to correct myopia.

b. Photocoagulation is a procedure to stop continuos fluid (ocular or blood) from oozing outwardly and for the removal of masses (protein or clots) from the iris. Performed by the controlled use of a laser (.e.g. xenon arc light of argon laser) by burning and creating scar formations.

c. Laser iridotomy is a surgical procedure for the treatment of glaucoma. It is performed by an incision creating holes upon the iris to allow fluid to move (flow) to the back of the eye. This procedure creates an artificial pupil.

D. ENABLING LEARNING OBJECTIVE (ELO) #4:

a. Photopic vision.

b. Mesopic vision.

c. Scotopic vision.

E. ENABLING LEARNING OBJECTIVE (ELO) #5:

a. Photosensitivity of the eye is one contributing factor that affects dark adaptation.

(1). Cones contain a chemical called iodosin. Cone cells pick up certain colors depending on their pigmentation sensitivity. These colors  are red, blue, yellow, or green.

(2).Rod cells are activated by a chemical known as rhodopsin (visual purple). Rhodopsin increases the rods effectiveness during dark  viewing periods. On an average it takes 30 to 45 minutes to achieve full effectiveness for your rods to be dark adapted for your night vision

b. Bleaching affect of the photoreceptor cells is another factor that affects dark adaptation.

(1). Bleaching of the cones and rods occurs when eyes are unprotected and exposed to direct bright light or solar glare.

(2). Cumulative unprotected exposure to bright light or solar glare may increase your dark adaptation time up to 3 to 5 hours to include negative  affects upon your night vision acuity.

(3). Duration of exposure of strobe light vs flare may have adverse affects to your night vision acuity and dark adaptation.

c. Poor nutrition and dietary habits is one more contributing factor that affects dark adaptation.

(1). Vitamin A deficiency hinders production of rhodopsin which is required for the effectiveness of the rods during dark viewing periods or  conditions.

(2). Consuming a well balanced diet that includes such foods as milk, cheese, carrots, green leafy vegetables, and organ meats (liver, heart  ect.) will provide sufficient percentages of Vitamin A that is required for  the production of rhodopsin.

WARNING: Do not supplement Vitamin A in its pure form, it may have a  toxic affect upon you physiologically. If supplementing for  vitamin A is necessary a one a day multi-vitamin is sufficient  for the production of rhodopsin. Consult your Flight Surgeon prior to supplementing for Vitamin A.

F. ENABLING LEARNING OBJECTIVE (ELO) #6:

a. Protective methods used to protect night vision include wearing of issued sun glasses and lowering of your tinted visor when exposed to high  ambient light or in combination of light reflecting off snow, sand, or water.

b. Adjust cockpit lighting to lowest readable level.

c. Dim down, lower the intensity of your aircraft’s interior and exterior lighting if mission permits.

d. Close or cover one eye briefly when unexpectedly exposed to a bright light when flying night unaided.

e. Use supplemental oxygen if available when flying above 4,000 feet.

f. Avoid brightly lit areas.

g. Use short ordinance burst.

h. Nutrition: consume a balanced diet.

i. Hydration: avoid dehydration by consuming water.

G. ENABLING LEARNING OBJECTIVE (ELO) #7:

ACTION: Identify limitations of night vision.

CONDITION: Given a list.

STANDARD: IAW FM 1-301 and TC 1-204.

NOTE: Limitations of night vision includes depth perception.

a. Depth perception.

(1). Perception maybe that you believe or assume that you are higher in altitude than you actually are (false interpretation or judgement of actual altitude related to poor depth perception).

(2) Use proper crew coordination to assist in determining your actual altitude.

(3) If mission permits use your search light or landing light and  if needed have your crewchief activate a chemical light and let it fall to the ground. Utilizing these methods will greatly assist you in obtaining clarity in relation to your aircraft’s position and altitude in regard to the ground or terrain below it.

b. Visual acuity.

(1) Visual acuity during the photopic period is at best 20/20 but during scotopic periods degrades to a possible 20/200 or greater.

(2) Loss or degraded image sharpness and clarity.

c. Blind spots (retinal).

(1). The day or physiological blind spot.

(2). The night blind spot.

d. Dark adaptation period.

(1). On an average it takes 30 to 45 minutes to dark adapt.

(2). The use of red lens goggles while remaining in a artificially lighted area, will assist in decreasing the average amount of time necessary to properly dark adapt.

(3).Cumulative and spontaneous exposure to bright lights or solar glare can increase your dark adaptation to 3 to 5 hours.

e. Loss of or degraded color vision.

(1). Loss of or degraded color perception due to decreased availability of natural ambient light. Use of cone cells is decreased or non-existent. Obstacles may not be seen or identified as rapidly as they would be during the day.

(2). Cone cells are bleached out so you may only see colors to include shades of gray, black, and white. This can only intensify your visual limitations during night unaided flying.

(3). Rod cells are used primarily at night to identify the outline of obstacles (silhouette recognition) which will assist you in determining their shapes and sizes. This may be performed subconsciously by memory, which may result in a aircraft mishap such as blade strikes, mid-air collisions, crashes and near misses.

H. ENABLING LEARNING OBJECTIVE (ELO) #8:

ACTION: Identify the cues of depth perception.

CONDITION: Given a list.

STANDARD: IAW FM 1-301 and TC 1-204.

a. Binocular cues depend on the slightly different view each eye has of an object. Binocular perception is of value only when the object is close enough to make a perceptible difference in the viewing angle of both eyes. Distances are usually so great in the flight environment that these cues are of little value. These cues operate on more of a subconscious level than does monocular cues. Study and training will not greatly improve them.

b. Monocular cues are derived from experience and are subject to interpretation.

(1). Geometric perspective occurs when objects appear to have different shapes when viewed at varying distances and from different angles.

(a) Linear perspective occurs when parallel lines tend to converge as distance from observer increases.

(b) Apparent foreshortening occurs when viewing from a distance, the shape of an object appears elliptical (narrow), but as distance is decreased the true shape is revealed.

(c) Vertical position in the field occurs when objects or terrain features that are farther away appear higher on the horizon than those that are closer to the observer.

(2). Retinal image size occurs when an image is focused upon the retina and is perceived by the brain to be of a given size.

(a). Known size of objects occurs when the closer an object is to an observer, the larger its retinal image. Through experience, the brain learns to estimate the distance of familiar objects by the size of its retinal image.

(b). The increasing or decreasing size of objects is used to judge whether an object is moving towards or away from an observer by its increasing or decreasing retinal image size.

(c). Terrestrial association is the comparison of one object with another object of known size to help determine the relative size and apparent distance of the object from the observer.

(d). Overlapping contours or interposition of objects is when objects overlap and the overlapped object is farther away.

(3). Aerial perspective is when distant information can be gained by the clarity of an object or by the shadow that is cast by an object.

(a). Fading colors or shades occurs when objects viewed through haze, smoke, or fog are seen less distinctly and appear to be at greater distance than they actually are. If atmospheric transmission of light is unrestricted, an object is seen more distinctly and appears to be closer than it actually is.

(b). Discrete details or texture is lost or is less apparent with distance.

(c). All objects will cast a shadow if there is a light source. The direction the shadow is cast depends upon the position of the light source. If the shadow is cast towards an observer then the object is closer than the light source.

(4). Motion parallax (one of the most important cues to depth perception) is the apparent, relative motion of stationary objects as viewed by a moving observer. Near objects appear to move past or opposite the landscape. Far objects seem to move in the direction of motion or remain fixed. The rate of apparent movement depends on the distance the observer is from the object. Rapidly moving objects are judged to be near while slow moving objects are judged to be distant.

I. ENABLING LEARNING OBJECTIVE (ELO) #9:

ACTION: Identify the methods to protect vision acuity from flight hazards.

CONDITION: Given a list.

STANDARD: IAW FM 1-301 AND TC 1-204.

a. Glare from direct, reflected, or scattered sunlight causes discomfort, reduction in visual acuity, and cumulative effects on dark adaptation for night flying. To reduce or eliminate the discomfort, every aviator should wear their issued sunglasses and lower their tinted visor as necessary during day flight. Day blindness can occur in areas of extreme solar glare (snow, desert, and water environments).

b. Bird strike hazards may always be present both day or night at lower levels of flight. Cockpit windshields should be able to withstand a bird strike, but the potential exists for shattering of the windshield. Further protection is necessary by lowering your clear or tinted visors at the beginning of the flight that way if this hazard should occur, your eyes will be protected from the objects penetrating the windshield to include glass fragments.

c. Lasers produce light that is amplified by a stimulated emission of radiation through one or a series of multiple prisms. The beam of light produced is usually less than one inch in diameter.

(1). Some laser sources produce the beam of light in the visible portion of the radiation spectrum and can be seen. Others produce the light outside the visible spectrum (infrared or ultraviolet) and are invisible.

(a). Over long distances, the beam progressively becomes wider reducing its energy (strength or intensity).

(b). Some laser devices have sufficient energy to severely injure and burn the eyes or skin.

1. Range finders.

2. Target designators.

(c). Some military lasers produce a beam that is 1 meter in diameter at 1 kilometer and 2 meters in diameter at 2 kilometers.

1. At these distances lasers can irradiate the whole body.

2. If the energy, intensity of the laser is high enough, it can burn clothing, skin, or any part of the body exposed to it. However, most lasers are not powerful enough to generate burns.

(2). Sensitivity of the eyes related to lasers.

(a) The lens focuses and concentrates (refracts) light that enters the eye upon the retina. Because of this the lens its self is very sensitive to injury from any type of laser.

(b) The concentration of energy which is focused (refracted) from the lens to the back of the eye (the retina) can be increased 100,000 times greater then the energy entering the eye.

(c) The amount of injury or damage to the eye depends on the type of laser your eye was exposed to, the energy output of the laser, duration of time exposed, and the distance of your exposure between yourself and the source of the laser.

(3) Types of possible burn injuries associated with lasers.

(a) Tiny lesions on the back of the eye (retinal layers).

(b) Severe burns effecting vast body portions.

(c) Flash blindness.

(d) Impaired night vision.

(4) Protective measures used to prevent laser injuries.

(a) Passive measures consist of taking cover, getting out of  the laser beam, and use any protective gear that is available associated towards lasers.

1. Use of protective goggles B-LPS (Ballistic and Laser Protective Eyewear).

2. Use of night vision imaging systems (Night vision image devices/NVDs) with mounted filters decrease the light amplification of the laser as it enters the NVD through the systems filters first than optics.

3. Squinting can limit a small amount of laser energy that enters the eye.

(b) Active protective measures consist of the following.

1. Countermeasures taught or directed by your commander or leader.

2. Maneuvers.

a. Applying evasive action.

b. Scanning the battlefield with one eye or monocular optics.

d. Nerve agent hazards are always a possibility and can be present during night operations.

(1) How timely you identify the physiological effects of nerve agents during night operations may determined the success and survivability of your crew and its mission.

(a) When direct contact occurs, minute amounts may cause miosis, constriction of the pupils. Pupils will not dilate (enlarge) in low ambient light as they would normally. Chemical alarms may not detect presence of nerve agents.

(b) Exposure time required to cause miosis depends on the agent concentration and the cumulative effects of repeated exposure.

(c) Symptoms range from minimal to severe depending on agent’s concentration and duration of exposure.

 1. Severe miosis may persist for 48 hours or longer after onset of exposure.

2. Complete recovery may take up to 20 days or longer.

(2) Insidious onset occurs usually but not always painful. There will be some loss of night vision among personnel exposed. Refer all exposed personnel to the flight surgeon immediately before performing flight duties or aircraft maintenance.

J. ENABLING LEARNING OBJECTIVE (ELO) #10:

ACTION: Identify the effects of the self-imposed stresses.

CONDITION: Given a list of self-imposed stresses and their functions.

STANDARD: IAW FM 1-301, TC 1-204, and AR 40-8.

a. Drugs.

(1). Illness, degradation in motor skills, awareness level, and reaction time are all possible contributing side effects related to drugs.

(2). Refer to AR 40-8 for restrictions for drug use while on flying status. Self-medicating is not authorized consult Flight Surgeon for approval of drug use (medications).

b. Exhaustion.

(1). Poor physical condition and exercise, lack of rest, and inadequate sleeping patterns or habits are all contributing factors leading to exhaustion.

(2) Common side effects related to exhaustion are altered concentration, awareness, attentiveness, increased drowsiness, and ineffective night vision viewing techniques (related to staring not scanning).

c. Alcohol.

(1) Long lasting physiological effects related to the consumption of alcohol.

(2) Detrimental effects related to the consumption of alcohol include poor or altered abilities upon judgement, decision making, perception, reaction time, coordination, and scanning techniques (tendency to stare at objects).

(3) Histotoxic hypoxia is the poisoning of the blood stream causing interference with the use of oxygen by body tissues (decreased tissue perfusion).

(4) One once of alcohol will place you at 2,000 feet physiologically.

a. Tobacco causes hypemic hypoxia which is the greatest threat to night vision.

(1) Effects of tobacco (smoking of cigarettes) decreased night vision viewing capability by an average of 20 percent at sea level and increased chance of becoming a possible hypoxia casualty when flying at higher altitudes such as for example instrument training or mission flight at 6,000 to 7,000 feet.

(2) The effects of smoking (hypemic hypoxia) places you physiologically at 5,000 feet.

(3) Hypemic or anemic hypoxia is caused by the reduction of the oxygen carrying capacity of the blood (via the red blood cells- RBCs) in direct relation to the carbon monoxide binding with the hemoglobin not allowing or severely decreasing the amount of oxygen binding with the hemoglobin as it should normally (vascular perfusion exchange of gases).

(4) Carbon monoxide has an affinity for hemoglobin 200-300 times greater than oxygen.

Example: An individual smokes 3 cigarettes in rapid succession or 20 to 30 cigarettes within a 24 hour period, the carbon monoxide content of the blood is raised 8 to 10 percent. The physiological effect at ground level is the same as flying at 5,000 feet. Even more importantly, the smoker has lost approx. 20 percent of the night vision capability at sea level.

b. Hypoglycemia and nutritional deficiency.

(1). Effects of hypoglycemia and nutritional deficiency results in hunger pains, distractions, breakdown in habit patterns, and shortened attention span.

(2). Contributing factors leading to low blood sugar (Hypoglcemia) and nutritional deficiency occurs skipping, missing, or postponing meals.

(3). Vitamin A deficiency will hinder production of rhodopsin. A balanced diet of foods should include eggs, butter, cheese, liver, carrots, and most green leafy vegetables.

K. ENABLING LEARNING OBJECTIVE (ELO) #11:

ACTION: Identify the proper night vision viewing techniques.

CONDITION: Given a list.

STANDARD: IAW FM 1-301 and TC 1-204.

a. Scanning.

(1). Stop-turn-stop-turn technique that is initiated approximately 500 meters out, the scanning continues until just a few feet in front of you.

(2). Ten degree circular overlap with just 2-3 second stops in order to prevent the rhodopsin from bleaching out the image.

b. Off-center viewing can be used to compensate for the night blind spot.

(1). You view an object by looking focusing ten degrees above, below, or to either side of the object your viewing in order to maintain visual reference of the object so as not to bleach it out and lose sight of the object.

(2). Ten degree circular overlap and off-center viewing are used in combination as in one and the same when it comes to night unaided viewing.

L. ENABLING LEARNING OBJECTIVE (ELO) #12:

ACTION: Identify the physiological effects of Night Vision Devices (NVDs).

CONDITION: Given a list.

STANDARD: IAW TC 1-204.

a. The immediate effects after viewing through NVDs to unaided viewing is decreased ability to perceive accurate depth perception, distance estimation, degree of contrast, discoloration of objects (chromatic), and the possibility of induced spatial disorientation.

b. Chromatic adaptation is a discoloration of objects viewed with the unaided eye after viewing through NVDs (anvis) for an extended period of time. This is a normal physiological response. It causes no discomfort and will disappear or subside within three to five minutes on the average. It will take on the average this amount of time to regain your dark adaptation and night vision acuity to the thirty to forty minute level-degree of effectiveness.

c. Spatial disorientation maybe induced by the following:

(1) Aircraft bank greater than 30 degrees.

(2) A scanning technique that is too rapid.

(3) Unfamiliar perception related to lack of NVG experience.