AOPA Pilot Magazine - April 2020 - 28

FLY WELL

BY DR. JONATHAN M. SACKIER

Green eggs, ham, and Isaac Newton
Color vision plays an important role in flying
THEODOR "TED" SEUSS GEISEL, better known as Dr.
Seuss, wrote Green Eggs and Ham, a book about refusal
that was banned in Maoist China for its political tone.
Eggs and ham are not usually green and eating such discolored, potentially spoiled food might induce physical
harm. Blue is not the correct color for runway lights; the
ability to spot that might prevent physical harm-and an
embarrassing conversation with the FAA.
In addition to defining the laws of gravity that
pilots joyously flout, Sir Isaac Newton maintained that
objects reflect a certain wavelength of light, absorbing
all others; it is the reflected beams we experience as
color. So Newton's apple is not inherently red, it just
reflects that particular part of the spectrum. Objects
like a runway can appear black because all wavelengths
are absorbed, and runway lights are white because all

Although one can adapt to driving a car if
color blind, for instance by knowing what
order traffic lights change, pilots have other
issues to contend with.

DR. JONATHAN
SACKIER is a private

pilot and surgeon.
He is a resource
for AOPA Pilot
Protection Services.

28 | AOPA PILOT April 2020

wavelengths are reflected. Red lights tell us to hold, a
green light from the tower invites us to land our nonradio aircraft, and blue marks a taxiway; combining
these three can produce all the colors of the spectrum,
and knowing which is which is important to pilots.
Light strikes the cornea, a membrane covering the eye;
this and an underlying lens focus the image, upside down,
projecting it onto the retina. Here, millions of specialized
cells, rods and cones, convert light into nerve signals that
are transmitted to the brain via the optic nerve, and with
a nod to aerobatics, the brain flips images right side up.
About 120 million rods are gathered around the periphery
of each eye and are best suited to interpreting dim light,
which also seems less colorful to us.
Centrally, 5 million to 6 million cones are mission critical for color and sharp vision; they are divided into three
types, some handling long (red), some medium (green),
and some short (blue) wavelengths. As roughly 60 percent
of cones are configured to respond to warm tones (yellow
to red), we can interpret more nuanced colors at that end

of the spectrum. The combined signals allow our brain to
dictate that a chosen tie definitely clashes with that shirt.
Color vision impairment is much more common
in males. Roughly one in 12 men, usually of northern
European stock, and one in 200 women are so affected:
inability to recognize differences between red and green,
the most common defect; or, less often, problems discerning blue from yellow. Gray days are common flying
in the northeast winter, but zero color differentiation-
achromatopsia, only seeing shades of gray-is rare and
accompanies poor general vision; lazy eye; preference
for dim light; and nystagmus, eyes that flicker incessantly.
As one might conclude, missing or malfunctioning
cones might lead to some degree or severity of color
"blindness" in either all lighting conditions or dim light.
The condition usually afflicts both eyes, is congenital
(present at birth), is of genetic origin, and does not
change much with age. Other causes are glaucoma or
macular degeneration, head or eye trauma, various diseases (e.g., diabetes, Parkinson's, leukemia, Alzheimer's,
sickle cell anemia), medications (hydroxychloroquine to
treat rheumatoid arthritis), and alcoholism.
Color blindness may not be diagnosed unless a color
test is conducted, coming to light (pun intended) when a
parent endeavors to teach a child color names. Developed
more than 100 years ago by Japanese ophthalmologist
Ishihara Shinobu, the eponymous color charts display
embedded numbers or shapes seen-or not-in colorful circles. Congenital color vision deficiency cannot
be treated, but if there is an underlying cause as above,
addressing that may improve the situation.
Although one can adapt to driving a car if color
blind, for instance by knowing what order traffic lights
change, pilots have other issues to contend with, such
as not landing on taxiways. You can read about requirements for flight and color vision in the FAA's Guide for
Aviation Medical Examiners (faa.gov).
As pilots, we see many great sights, but the privilege to fly depends partially on color vision. If you
already have your certificate, you must have passed
the color vision test, so any change would suggest a
causative disease or condition as above-another good
reason to see an eye doctor annually.
AOPA
EMAIL DrJonathanSackier@gmail.com

http://www.faa.gov

AOPA Pilot Magazine - April 2020

Table of Contents for the Digital Edition of AOPA Pilot Magazine - April 2020