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How the Eye Works

To understand how the human eye works, first imagine a photographic camera—since cameras were developed very much with the human eye in mind.

How do we see what we see?

eye diagramLight reflects off of objects and enters the eyeball through a transparent layer of tissue at the front of the eye called the cornea. The cornea accepts widely divergent light rays and bends them through the pupil—the dark opening in the center of the colored portion of the eye.

The pupil appears to expand or contract automatically based on the intensity of the light entering the eye. In truth, this action is controlled by the iris—a ring of muscles within the colored portion of the eye that adjusts the pupil opening based on the intensity of light. (So when a pupil appears to expand or contract, it is actually the iris doing its job.)

The adjusted light passes through the lens of the eye. Located behind the pupil, the lens automatically adjusts the path of the light and brings it into sharp focus onto the receiving area at back of the eye—the retina.

An amazing membrane full of photoreceptors (a.k.a. the “rods and cones”), the retina converts the light rays into electrical impulses. These then travel through the optic nerve at the back of the eye to the brain, where an image is finally perceived.

A delicate system, subject to flaws.

It’s easy to see that a slight alteration in any aspect of how the human eye works—the shape of the eyeball, the cornea’s health, lens shape and curvature, retina problems—can cause the eye to produce fuzzy or blurred vision. That is why many people need vision correction. Eyeglasses and contact lenses help the light focus images correctly on the retina and allow people to see clearly.

In effect, a lens is put in front of the eye to make up for any deficiencies in the complex vision process.

The main parts of the human eye include:

  • Cornea: transparent tissue covering the front of the eye that lets light travel through
  • Iris: a ring of muscles in the colored part of the eye that controls the size of the pupil
  • Pupil: an opening in the center of the iris that changes size to control how much light is entering the eye.
  • Sclera: the white part of the eye that is composed of fibrous tissue that protects the inner workings of the eye
  • Lens: located directly behind the pupil, it focuses light rays onto the retina
  • Retina: membrane at the back of the eye that changes light into nerve signals
  • Rods and cones: special cells used by the retina to process light
  • Fovea: a tiny spot in the center of the retina that contains only cone cells. It allows us to see things sharply.
  • Optic Nerve: a bundle of nerve fibers that carries messages from the eyes to the brain
  • Macula: a small and highly sensitive part of the retina responsible for central vision, which allows a person to see shapes, colors, and details clearly and sharply.

 

Special thanks to the EyeGlass Guide, for informational material that aided in the creation of this website. Visit the EyeGlass Guide today!

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Dear Northwood Vision patient,

Here is what we are asking you to do to make a smaller exposure footprint:

  1. If you have any symptoms of loss of taste or smell, upset stomach/diarrhea coughing, fever, difficulty breathing, running nose please reschedule your appointment in 30 days or more.
  2. Wash your hands or use sanitizer immediately upon entering.
  3. Try not to touch any surfaces in the office you do not have to touch (you can push our door open with your foot! Try not to touch your face!)
  4. If you are trying on glasses, we will collect them from you for proper cleaning.
  5. Contact lenses can be shipped to you at no cost with an active rx (minimum 2 boxes)
  6. We will ask that if possible you come alone to the appointment. Guests can wait outside or in the car unless they need to be with you..
  7. If you have been exposed please wear a mask or reschedule in case you are an asymptomatic carrier, masks are encouraged to be worn by each patient if you have one.
  8. We will extend Contact lens prescriptions up to 6 months if recently expired and can direct ship an order to you if you see clearly and your eyes are feeling healthy.
  9. For a fee, we can ship your glasses to you if desired and you can have them adjusted after the shelter in place order is lifted.

Thank you for your patience and understanding during this stressful and trying time. May God bless each of you and keep you well.

Dr. Christopher K. Keats, OD

What is an Eye Emergency? Read more

Routine Care: “I see pretty well in my glasses or contact lenses. I just want to update my frame and / or get some new lenses to optimize my vision. I don’t have any pain or headaches and my eyes feel good and look normal in the mirror to me. I have never been told I have a disease in my eye that needs to be managed. I should definitely wait to come in until the “Shelter at Home” mandate is over. If I am a contact lens wearer, I understand Dr. Keats will allow me to get 3-6 months of contact lenses mailed to me even if my contact lenses are recently expired or close to expiring.”

Emergent Care: “I see poorly and am having difficulty functioning to drive, read, or see my computer. It is affecting my work. Waiting to be seen in 2 months would be very difficult for me to conduct my life.” Another form of emergent care… “I have other symptoms like headaches, red eyes, discharge, or I might have a disease that threatens my sight like diabetes, macular degeneration, glaucoma, a recent onset of flashes and floaters in my vision and so on.” A final type of emergent care would be a patient who realizes, “I am a patient who has a previously scheduled appointment for a medical condition Dr. Keats is managing to protect my sight, so I should plan on coming in for my visit. However, if my overall health is poor and the benefit to risk ratio says I should push this appointment off until the “Shelter at Home” mandate is lifted, it may be wise for me to reschedule for a later date.” In summary, emergent care means it is important that you be seen quickly for the protection of your visual health and current discomfort, or medical health, so you can function to do your work efficiently now and in the future.