A big trend right now is putting honey in your eyes
in order to change the color of your iris.
Putting honey in your eyes will make you go blind.
Honey cannot even penetrate the cornea deep enough
to get to the iris, but if it did, you would be blinded instantly.
Or at least get glaucoma.
Melanin is the pigment found in nearly all organisms (except arachnids). This is the
pigment that dyes our hair, skin, and eyes. Naturally, melanin is black or brown. So technically
everyones eye color is the same; all of our irises are dark brown or even black.
Obviously, this isn't the case because I have green eyes and many people have other colored
eyes besides brown. The reason we see different colors of eyes is due to the same reason the
sky is blue: Rayleigh scattering. Named after the British physicist, Lord Rayleigh, Rayleigh
scattering is the elastic spreading of light due to particles much smaller than the wavelength
of the light that passes through them. Things like molocules, or atoms. In the case of the
iris in our eye, it is small particles of melanin.
Brown eyes have a large concentration of melanin and thus appear the actual color of melanin
itself. The concentration of melenin is so high that Rayleigh scattering cannot be seen.
Since blue eyes have much less melanin, Rayleigh scattering can be seen more prominently. Green
and hazel eyes have a bit more melanin than blue eyes but still less than brown eyes.
They are a mixture of the actual pigment and the light scattering of melanin particles.
In extreme cases of albinism, the amount of melanin in the eye is close to none; the iris
is actually transparent and will appear red due to the blood vessels in the eye.
But genetically speaking, what decides what colors our eyes will be? Well, scientists
are not completely sure. It is possible that sixteen different genes could be responsible
for determining the eye color of people. However, the main genes found to determine eye color
are OCA2 and HERC2. Both of these genes are localized in Chromosome 15. It is impossible
to predict with 100% confidence the eye color of a baby only knowing the genes of the parents,
however, we can get close. A great program that I found interesting is the TheTech.org's
Eye Color Calculator. It takes into consideration your parents eye color and calculates your
future child's eye color using genotypes. A good rule of thumb for eye color genetics
is that darker colors tend to dominate lighter colors. So brown-blue parent's are more likely
to have brown eyed children. As babies age into children and then into
adults, their eye colors can change due the the increase or decrease of melanin in the
iris. Many babies are born with light colored eyes that can darken over the first few years
of their life. Many people say that their eye pigment changes
with emotion, however this notion is completely innaccurate. Ivan Schwab, a professor of ophthalmology
at University of California, explains the perceived eye color change due to emotion
is only due to the surrounding colors; [change shirts] such as a colored shirt. Red blood
vessels in your eyes from anger will cause eyes to appear lighter from the contrast.
Dialated pupils from sadness or greif can cause the iris to appear darker.
Since the "color" of our eyes is only perceived due to light scattering, I would not be completely
out of line to say that emotions cause the perceived color to change. However the actual
pigment and wavelength of light do not change; merely the contrast between colors. If your
eyes were to actually change pigments, this can be extremely dangerous and may be a sign
of a ocular disease. If you wake up one morning with different eye colors, I would recommend
you go to the optomitrist immediately. A very interesting ocular condition is that
of heterochromia. Very occationally, people and animals are born or develop two different
colored eyes. It is caused by having relatively different amount of melanin in each eye. This
condition can actually happen in the same eye causing half or sections of the iris to
be vastly different colors. Most of the time heterochromia is a genetic mutation, but can
also be caused by disease or injury.