Eye color – Did you know?

1) How is eye color determined?

   Eye color is determined by two distinct factors.

  • The pigmentation of the eye’s iris – The iris is a muscle and the colored part of the eye. The amount of melanin present determines eye color.
  •  The scattering of light in the stroma of the iris – Rayleigh scattering is a similar phenomenon that accounts for the blueness of the sky. Blue and green pigments are not present in the iris of humans or ocular fluid.

2) Does eye color change with age?

Photo courtesy of Javier Manso on Flickr

Photo courtesy of Javier Manso on Flickr

  • Yes. Most babies with European ancestry have light-colored eyes before the age of one. As a child grows, melanocytes produce melanin. Melanocytes are cells found within the iris of human eyes. Most eye color changes occur when the child is around one year old, however it can happen up to three years of age.
  • Eye color (lightening or darkening) may change with age. This occurs in 10 to 15 percent of the population. However, if your eye color changes dramatically as an adult, it is important to schedule an examination with your eye doctor. Eye color changes may indicate certain diseases, such as Fuch’s heterochromic iridocyclitis, Horner’s syndrome or pigmentary glaucoma.

 3) Is it possible to see emotions such as anger or love in the eyes?

Yes. Certain emotions can change both the pupil size and the iris color. Pupil size gets larger in dimmer lighting and smaller in brighter lighting. When pupil size changes, pigment in the iris compress or spread apart, which can change the eye color.

4) What makes eyes green?

The color of green eyes is not a result of iris pigmentation. Green eyes are due to a combination of amber or light brown pigmentation of the stroma. There is a low or moderate concentration of melanin. The green appearance is due to the Rayleigh scattering of reflected light.

5) What can I do to change my eye color?

Color contact lenses are available if you want to change your eye color. There are even colored contact lenses with patterns for occasions such as Halloween. Since contact lenses are medical devices, visit your doctor of optometry for a contact lens fitting.

~Melissa Barnett, OD, FAAO
California Optometric Association
http://www.coavision.org

Advertisements

Anatomy of the Eye 101

Courtesy of DVIDSHUB on Flickr

Courtesy of DVIDSHUB on Flickr

As a teacher and a doctor, I talk about the eye on a daily basis to my optometry students and patients alike.  I often use examples that my optometry students and patients can relate to.  The eye is like a high definition video camera that captures images of the visual world in real time.  If any part of your eye, that is, your “human video camera,” is affected or broken you may experience varying degrees of blurry vision, discomfort, or other common symptoms.  If you seek professional evaluation by your optometrist at the first inkling that something is out of sync, he or she can “fix or repair” your eye and get you back on a healthy track.

So let’s talk about the eye from front to back.

To start, the eyelids and lashes are the first visible structures to the outside observer.  Not only are the eyelids and lashes beautiful, but they also serve to protect the eye.  The eyelids spread lubricating tears like that of a windshield wiper across the surface of the eye with just a single blink, and the lashes act like specialized antennae sensing the smallest incoming offending particles.

Next, the conjunctiva is known to us as the “white” part of the eye.  This too is visible to the outside observer.  There are times that the conjunctiva may get inflamed or infected which results in that unwanted “pink eye” or conjunctivitis.

Much respect and attention has been given to the 5-layer-thick cornea as the clear window of the eye.  This is the layer where contact lenses are applied to correct nearsightedness or farsightedness.  Many successful surgeries like LASIK and corneal transplants have been performed on this tissue.

The anterior chamber and the vitreous are two compartments that give form to the eye and serve as conduits for circulating important fluids from one part of the eye to another.

Courtesy of entirelysubjective on Flickr

Courtesy of entirelysubjective on Flickr

The color part of the eye is called the iris.  It comes in many different colors and hues including brown, hazel, green, blue, and even violet.  The purpose of the iris is to regulate the amount of light that enters the eye.  Like that of a camera shutter, the iris controls the size of the pupil thus preventing under or over exposure of the picture of the visual world that is being seen.

The crystalline lens sits right behind the iris.  And similar to a camera lens, the human lens helps focus the things we see.

The retina, optic nerve, and macula can all be found way back in the eye.  The retina is the nervous tissue of the eye and is made up of 10 important layers. It gathers nervous signals and funnels it to the optic nerve.  As the name implies, the optic nerve is the nervous cable that connects the eye to the sight center in the back of the brain.  The macula allows you to see the finest details in vision.

This sums up the crash course on the Anatomy of the Eye 101.  Next time you are at your friendly optometrist’s office, just imagine the different parts of your eye being systematically looked at.

~By Judy Tong, OD