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

Dry Eye Disease

If you ever have stinging, burning, gritty or sandy sensation, excessive tearing or itchy eyes, you may have symptoms of dry eye disease.

Dry eye disease is a condition where you don’t have enough tears or have poor quality tears to lubricate and nourish the eye. Tears maintain the health of the front surface of the eye and provide good vision. Dry eye disease is a common and often chronic problem, particularly in older adults. Advanced dry eyes may damage the front surface of the eye and impair vision.

The front surface of the eye is called the cornea. With each blink of the eyelids, tears are spread across the front surface of the eye. Tears are produced by several glands in and around the eyes. The tear film is composed of nutrients, electrolytes, proteins and lubricants. Tears provide lubrication, reduce the risk of eye infection, clear the eye of foreign matter, and keep the surface of the eyes intact and clear. Tears drain from the eyes into small drainage ducts called puncta in the corners of the eyelids, which drain in the back of the nose.

Courtesy of Clearly Ambiguous on Flickr

Courtesy of Clearly Ambiguous on Flickr

If there are any irregularities in the tear film, symptoms of dry eye may manifest. Dry eye disease may limit daily activities including reading, driving, working on the computer or wearing contact lenses.

Many different factors cause dry eye. These are some of the most common:

1) Hormones: Dry eye disease is more common in people 50 years old or older. Hormonal changes that are common in women experiencing menopause can cause dry eye.

2) Systemic diseases: Other systemic diseases including diabetes, glaucoma, Sjogren’s syndrome, lupus and rheumatoid arthritis can exacerbate the symptoms of dry eye.

3) Medications: Medications including antihistamines, hormonal replacement therapy and androgen therapy may contribute to dry eyes.

4) The environment: Environmental factors such as pollen or allergies, working on the computer or contact lens wear can make dry eyes worse.

Dry eye disease is diagnosed by patient history. In diagnosing dry eye disease, your doctor of optometry will evaluate the symptoms, general health problems, medications or environmental factors that contribute to dry eye disease. Your doctor will perform an external examination of the eyes including the eyelid structure and blink dynamics. Your doctor will evaluate the eyelids, cornea and conjunctiva is performed using bright light and magnification. Measurement of the quantity and quality of tears is assessed for any abnormalities. From this information, your doctor of optometry can determine if you have dry eyes and advise you on treatment options.

Treatments for dry eyes include:

  • over the counter artificial tears,
  • punctal plugs (small plastic pieces that close the ducts that drain tears out of the eyes),
  • eyelid hygiene,
  • dietary supplementation,
  • or a prescription eyedrop called Restasis (cyclosporine 0.05%).

If you experience any of theses symptoms, contact your doctor of optometry and ask for a dry eye evaluation.

~ Melissa Barnett, OD, FAAO