n 

Vision is a pilot’s most important sense to 

flight. Most pilots are familiar with the o

start flying, we know whether we have normal farsighted or nearsighted, or have other visual scription lenses—contacts or eyeglasses—have lwith us when we fly, just as a backup. But, visiin optics. Seeing involves the transmission of ligsurface of the cornea to the interior surface otransference of these signals to the brain. 

The Anatomy of 

Light from an object enters the eye through th

the pupil. 

The opening (dilation) and closing (constrict

iris, which is the colored part of the eye. The fuof the diaphragm of a photographic camera: to 

The lens is located behind the pupil and its fu

of the retina. 

The retina is the inner layer of the eyeball tha

rods and cones. The function of the retina is sigraphic camera: to record an image. 

The cones are located in higher concentration

retina known as the macula, that measures abcenter of the macula has a very small depression only. The cones are used for day or high-intenwith central vision to detect detail, perceive col

The rods are located mainly in the periphery 

10,000 times more sensitive to light than the intensity or night vision and are involved with references including objects (fixed and moving) to detect detail or to perceive color. 

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p 

Light energy (an image) enters the eyes and is transformed by the cones and rods 

into electrical signals that are carried by the optic nerve to the posterior area of the brain (occipital lobes). This part of the brain interprets the electrical signals and creates a mental image of the actual object that was seen by the person. 

The Anatomical Blind Spot 

The area where the optic nerve connects to the retina in the back of each eye is 

known as the optic disk. There is a total absence of cones and rods in this area, and, consequently, each eye is completely blind in this spot. Under normal binocular vision conditions this is not a problem, because an object cannot be in the blind spot of both eyes at the same time. On the other hand, where the field of vision of one eye is obstructed by an object (windshield post), a visual target (another aircraft) could fall in the blind spot of the other eye and remain undetected. 

The Night Blind Spot 

The “Night Blind Spot” appears under conditions of low ambient illumination 

due to the absence of rods in the fovea, and involves an area 5 to 10 degrees wide in the center of the visual field. Therefore, if an object is viewed directly at night, it may go undetected or it may fade away after initial detection due to the night blind spot. 

• The Fovea 

The fovea is the small depression located in 

contains a high concentration of cones but no how small a one-degree field is, and to demonsyour pocket and tape it to a flat piece of glass1⁄2 feet from the mounted quarter and close oncovered by the quarter is a one-degree field, sim

Now we know that you can see a lot more 

do you know how little detail you see outsidoutside of a ten-degree cone, concentric to the about one-tenth of what you can see within thing aircraft, if you are capable of seeing an aircfeet away, with peripheral vision you would deusing foveal vision we can clearly identify an aihowever, using peripheral vision (outside the fodistance of .7 of a mile to recognize the same learning to fly, your instructor always told you keep your eyes scanning the wide expanse of sp
r 

Types of Vision

Photopic Vision. During daytime or high intensity artificial illumination conditions, the eyes rely on central vision (foveal cones) to perceive and interpret sharp 

images and color of objects. 

Mesopic Vision. Occurs at dawn, dusk, or under full moonlight levels, and is 

characterized by decreasing visual acuity and color vision. Under these conditions, a combination of central (foveal cones) and peripheral (rods) vision is required to maintain appropriate visual performance. 

Scotopic Vision. During nighttime, partial moonlight, or low intensity artificial 

illumination conditions, central vision (foveal cones) becomes ineffective to maintain visual acuity and color perception. Under these conditions, if you look directly at an object for more than a few seconds, the image of the object fades away completely (night blind spot). Peripheral vision (off-center scanning) provides the only means of seeing very dim objects in the dark. 

Factors Affecting Vision 

The greater the object size, ambient illumination, contrast, viewing time, and atmospheric clarity, the better the visibility of such an object. During the day, objects can be identified easier at a great distance with good detail 

resolution. At night, the identification range of dim objects is limited and the detail resolution is poor. 

Surface references or the horizon may become obscured by smoke, fog, smog, 

haze, dust, ice particles, or other phenomena, although visibility may be above Visual Flight Rule (VFR) minimums. This is especially true at airports located adjacent 

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to large bodies of water or sparsely populated aences are available. Lack of horizon or surface flights, at night, and in low-visibility condition

Excessive ambient illumination, especially fro

faces inside the aircraft, clouds, water, snow, and may cause uncomfortable squinting, eye tearing

Presence of uncorrected refractive eye disord

— impaired focusing of distant objects), hypercusing of near objects), astigmatism (impaired fians), or presbyopia (age-related impaired focus

Self-imposed stresses such as self-medicatio

hangover effects), tobacco use (including withdprivation/fatigue can seriously impair your visio

Inflight exposure to low barometric pressure w

gen (above 10,000 ft during the day and abovpoxia, which impairs visual performance. 

Other factors that may have an adverse eff

windscreen haze, improper illumination of the cockpit and/or instruments, scratched and/or dirty instrumentation, use of cockpit red lighting, inadequate cockpit environmental control (temperature and humidity), inappropriate sunglasses and/or prescription glasses/contact lenses, and sustained visual workload during flight. 

Focusing 

The natural ability to focus your eyes is criti

know that normal eyes may require several secobetween near (reading charts), intermediate (mobjects (looking for traffic or external visual ref

Fatigue can lead to impaired visual focusing

or undershoot the target, and can also affect a pbetween near, intermediate, and distant vision. sual fatigue include blurred vision, excessive teaor orbital headaches, and burning, scratchy, or 

Distance focus, without a specific object t

quickly. If you fly over water or under hazy conbetween cloud layers at night, your distance foc

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If there is nothing specific on which to focus, your eyes revert to a relaxed intermediate focal distance (10 to 30 ft). This means that you are looking without actually seeing anything, which is dangerous. The answer to this phenomenon is to condition your eyes for distant vision. Focus on the most distant object that you can see, even if it’s just a wing tip. Do this before you begin scanning the sky in front of you. As you scan, make sure you repeat this re-focusing exercise often. 

Dark Adaptation or Night Vision Adaptation 

Dark adaptation is the process by which the eyes adapt 

for optimal night visual acuity under conditions of low ambient illumination. The eyes require about 30 to 45 minutes to fully adapt to minimal lighting conditions. The lower the starting level of illumination, the more rapidly complete dark adaptation is achieved. To minimize the time necessary to achieve complete dark adaptation and to maintain it, you should: 

avoid inhaling carbon monoxide from smoking or exhaust fumes get enough Vitamin A in your diet adjust instrument and cockpit lighting to the lowest 

level possible 

avoid prolonged exposure to bright lights use supplemental oxygen when flying at night above 5,000 ft (MSL) 

If dark-adapted eyes are exposed to a bright light source (searchlights, landing 

lights, flares, etc.) for a period in excess of 1 second, night vision is temporarily impaired. Exposure to aircraft anti-collision lights does not impair night vision adaptation because the intermittent flashes have a very short duration (less than 1 second). 

Visual Scanning 

Scanning the sky for 

other aircraft is a very important factor in avoiding midair collisions, and it should cover all areas of the sky visible from the cockpit. Most of us are instinctively alert for potential head-on encounters with another aircraft. Actually, a study of 50 midair collisions revealed that only 8% were head-on. However, 42% were collisions between aircraft heading in the same direction. So, compared with opposite-direction traffic, your chances of having a midair are over 5 times greater with an aircraft you are overtaking or one 

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that is overtaking you. It is necessary for you that allows the efficient scanning of the surrouncockpit instrumentation as well. You can accomshort, regularly spaced eye movements that brincentral (foveal) visual field. To scan effectively, sBegin scanning at the top of the visual field in finward toward the bottom. Use a stop-turn-stoeach stop should be at least 1 second but not lo

To see and identify objects under condition

looking directly at an object for more than 2 to 3 Instead, use the off-center viewing that consists (10 degrees above, below, or to either side) to lments to keep the object in sight. By switching to another every 2 to 3 seconds, you will continue to detect the object in the peripheral field of vision. The reason for using off-center viewing has to do with the location of rods in the periphery of the retina for night or low-intensity night vision (peripheral), and their absence in the center of the retina (fovea). Pilots should practice this off-center scanning technique to improve safety during night flights. 

A Word about Mono

A pilot with one eye (monocular), or with 

monocular (i.e. best corrected distant visual acu20/200), may be considered for medical certifiissuance procedures of Part 67 (14CFR67.401) 

A 6-month period has elapsed to allow for 

the adaptation period to monovision, an indivioccasional loss of balance. 

A complete evaluation by an eye specialist, 

Report of Eye Evaluation, reveals no pathologstability of the findings. 

Uncorrected distant visual acuity in the bette

rected to 20/20 or better by lenses of no greateequivalent. 

The applicant passes an FAA medical flight t

••••
Medical Facts f

Publication: AM-400-98

Written by: Melchor J. A

Prepared by

Federal Aviation Adm

Civil Aerospace Medic

Aerospace Medical Educa

To request copies of this brochure and 

FAA Civil Aerospace Me

Shipping Clerk, AA

P.O. Box 250

Oklahoma City, OK 

(405) 954-48

Other Pilot Safety Broch

Number TitleAM-400-94/2 Alcohol and Flying: A Deadly ComAM-400-95/2 Altitude Decompression SicknessOK05-0270 Carbon Monoxide: A Deadly ThrAM-400-03/2 Deep Vein Thrombosis and TravelAM-400-98/3 Hearing and Noise in AviationAM-400-91/1 Hypoxia: The Higher You Fly, the AM-400-97/1 Introduction to Human Factors in OK05-0005 Medications and FlyingAM-400-01/1 Physiological Training Courses for AM-400-91/2 Seat Belts and Shoulder HarnessesAM-400-95/1 Smoke!AM-400-00/1 Spatial Disorientation: Visual IllusAM-400-03/1 Spatial Disorientation: Why You SAM-400-05/1 Sunglasses for Pilots: Beyond the I

To view these pilot and passen

visit the Federal Aviation Admi

www.faa.gov/pilots/safety/p

Physiological Training C

If you are interested in taking a one-day av

with altitude chamber and vertigo demonstratioabout how to sign up for these courses that are oby visiting this FAA Web site:

www.faa.gov/pilots/training/airman_educatio

v

A Word about Contact Lenses 

Use of contact lenses has been permitted to satisfy the distant visual acuity requirements for a civil airman medical certificate since 1976. However, monovision 

contact lenses, a technique of fitting older patients who require reading glasses with one contact lens for distant vision and the other lens for near vision, ARE NOT ACCEPTABLE for piloting an aircraft. 

The use of a contact lens in one eye for distant visual acuity and a lens in the other 

eye for near visual acuity is not acceptable because this procedure makes the pilot alternate his/her vision; that is, a person uses one eye at a time, suppressing the other, and consequently impairs binocular vision and depth perception. Since this is not a permanent condition for either eye in such persons, there is no adaptation, such as occurs with permanent monocularity. Monovision lenses, therefore, should NOT be used by pilots while flying an aircraft. 

The Eyes Have It 

As a pilot, you are responsible to make sure your vision is equal to the task of flying—that you have good near, intermediate, and distant visual acuity because: 

Distant vision is required for VFR operations including take-off, attitude control, 

navigation, and landing 

Distant vision is especially important in avoiding midair collisions Near vision is required for checking charts, maps, frequency settings, etc. Near and intermediate vision are required for checking aircraft instruments 

Learn about your own visual strengths and weaknesses. Changes in vision may 

occur imperceptibly or very rapidly. Periodically self-check your range of visual acuity by trying to see details at near, intermediate, and distant points. If you notice any change in your visual capabilities, bring it to the attention of your Aviation Medical Examiner (AME). And, if you use corrective glasses or contacts, carry an extra pair with you when you fly. Always remember: Vision is a pilot’s most important sense. 

KEY POINTS 

The sharpest distant focus is only within a one-degree cone. Outside of a 10° cone, visual acuity drops 90%. Scan the entire horizon, not just the sky in front of your aircraft. You are 5 times more likely to have a midair collision with an aircraft flying in the 

same direction than with one flying in the opposite direction. 

Avoid self-imposed stresses such as self-medication, alcohol consumption, smoking, hypoglycemia, sleep deprivation, and fatigue. Do not use monovision contact lenses while you are flying an aircraft. Use supplemental oxygen during night flights above 5,000 ft MSL. Any pilot can experience visual illusions. Always rely on your instruments to confirm your visual perceptions during flight. 

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