For those of us blessed with the gift of sight, “seeing” is something that shapes us internally and externally every day. We make assumptions and decisions based on what is visual – with colors and imagery burning brightest among all the senses.

The eye is such a small part of the human body, yet each part within it works in concert to help maintain a normal, functioning organ.

Cornea
The front surface of the eye is called the cornea. It is a clear covering that is arched over the iris, or the colored part of the eye.

Aberrations to the shape of the cornea can cause nearsightedness, farsightedness and astigmatism. Having an astigmatism means that the cornea is not perfectly round, but instead is shaped more elliptical - like a football or lemon. While certain diseases such as keratoconus or a pterygium can cause astigmatism, it more commonly is due to the natural shape of the cornea.

Conjunctiva
Adjacent to the cornea is the conjunctiva. This is another clear covering of tissue that holds the superficial blood vessels that lay atop the visible white part of the eye known as the sclera.

With bouts of the viral condition commonly known as “pink eye,” it is this layer that becomes inflamed and causes the eye to take on a pinkish appearance. However, there are many other types of conjunctivitis that cause this appearance such as allergies, bacterial infections and even simple dryness.

Attached to the external eye behind the eyelids are six muscles which control all eye movement. If these muscles are not all working in perfect synchronization with those of the opposite eye, double vision will result. Some children are born with this imbalance which results in crossed-eyes or eyes that drift or do not track properly. Certain exercises can improve some of these muscle problems. More serious issues may require additional attention and even surgery.

Adults can also experience a sudden onset in weakness to one of these muscles and note double vision. The causes can range from a mild stroke to a tumor developing further back in the brain. When double vision occurs in adults, the immediate care of an eye care physician should be scheduled.

Iris
The iris is the colored part of the eye that controls how much light is let into the eye by adjusting the size of the pupil. It is a muscle that expands in dim light and contracts in bright light. When the pupil is very small, vision can appear to be slightly improved, which is one reason why people feel they can see better while reading in bright light.

Crystalline Lense
Just behind the iris is the crystalline lens. It is clear at birth - just like the lens of a camera or eyeglass. As it ages, the lens gradually becomes more hazy, cloudy or yellowed. When this stage occurs, it is deemed a cataract.

After the age of 55, many people experience changes to the lens. When vision becomes impaired to the point that strengthening the eyeglass prescription does not help, cataract surgery usually is offered.

While the need for cataract surgery never represents any medical emergency, waiting too long can cause the surgery to become more complicated if the cataract has become very dense. Cataract surgery is never performed with a laser. It must be manually removed, so that an implant can replace it. However, sometimes after cataract surgery, a film forms over the back of the implant and this is removed via laser.

Vitreous
The vitreous is the jelly-like substance that fills the eye’s internal cavity behind the lens. This is the part of the eye responsible for the floaters that many people see drifting into their field of vision. Floaters usually represent a benign separation from the back of the eye known as a posterior vitreous detachment. However, if flashes or loss of vision are noted following a new bout of floaters, a more severe condition known as a retinal detachment may have occurred and immediate care from an eye care practitioner is necessary to diagnose and prescribe proper treatment.

Retina
The retina is the back layer of the eye responsible for collecting the light and relaying it back to the optic nerve and brain so that vision may occur. Any damage to this tissue can result in severe vision loss.

The macular is contained within the retina and is the most sensitive part of it, responsible for maintaining detailed, sharp, central vision. If it starts to degenerate, as in the condition called age-related macular degeneration, significant loss to clarity will be noted centrally. However, it is the rest of the retina that is responsible for peripheral vision. Therefore, even if severe damage occurs to the macula, peripheral vision will remain intact, so that complete blindness does not result.

Optic Nerve
The optic nerve is the final recipient of the messages sent through the eye and collected to send back to the brain for visual processing. This part of the eye does not detect light itself and is the reason normal eyes have “blind” spots. Because the blind or missing information is filled in by what is viewed in the other eye, we never really experience true blind areas with normal vision.

The optic nerve measures approximately 25-30mm in length from the back of the eye to its entry point at the skull. Understanding this extremely close proximity explains why the eye can never be removed from its socket for any type of surgery.

Every microscopic part of the eye is a necessary contributor to maintaining good, comfortable vision. Because every part of the eye is susceptible to irregularities and microscopic diseases, annual eye examinations are recommended to protect vision and prevent minor medical issues from becoming more serious.

Anne Gregas, O.D., is board certified by the American Board of Optometry and the National Board of Optometry. Her office is in Melbourne. For more information call (321) 253-3550.