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How Do Eyes Work?

In order to understand macular degeneration, you first need to get a basic idea of the general anatomy of the healthy eye. The eye is the organ that helps us see, and though it may look like one whole, there are many different parts to the eye. Knowing which parts are responsible for what can help you better understand just how sight operates, and what happens when something goes awry, like in macular degeneration.

How do we see?

Sight is intricately linked to light. Light enters the eye through the cornea, then travels through the lens.1 These together help to focus the light onto the retina, which is located in the back of the eye. The retina then uses special light-sensing cells, called photoreceptors, to send signals to the brain via the optic nerve.1 The brain then interprets these signals, giving you an image.

Parts of the eye

parts of the eye including the iris, lens, choroid, and a more in depth view of the components of the retina

Cornea

The cornea can be compared to the windshield of a car. It is located at the front of the eye and is a clear window which transmits and focuses light entering the eye.1

Iris

The iris is the colored part of the eye, with the pupil in the center of it. The pupil dilates and contracts depending upon the amount of light that is present.1

Lens

The lens further focuses light onto the retina.1

Retina

The retina is in the back of the eye, containing cells called photoreceptors that sense light entering the eye. Those photoreceptors convert light into electrical signals that are sent to the brain via the optic nerve so they can be interpreted as images.1

Macula

The macula is the part of the retina that has the greatest number of light-sensitive cells, or photoreceptors. It is responsible for providing us with the ability to see things in the middle of our visual field, or central vision.1

Fovea

The fovea is the center of the macula that is responsible for sharp vision; it is most important for activities requiring fine detail such as reading.1

Retinal pigment epitehlium (RPE)

The retinal pigment epithelium (RPE) is a thin layer of pigmented supporting cells located between the retina and the choroid.It helps nourish the photoreceptors in the retina to keep them healthy.2

Choroid

The choroid is a layer that lines the back of the eye and contains both connective tissue and blood vessels. It is located between the retina and the sclera and provides oxygen and nutrients to the outer half of the retina.1

Retinal blood vessels

The retinal blood vessels (arterioles and venules) enter the eye through a channel in the optic nerve and provide oxygen and nutrients to the inner half of the retina.

Sclera

The sclera is the protective white outer layer of the eye.1

Optic nerve

The optic nerve is located in the back of the eye and acts as a cable to send signals from the eye to the brain.

Bruch’s membrane (BM)

Bruch’s membrane (BM) is between the RPE and the choroid, regulating exchanges of nutrients, fluid, oxygen, and waste products between the retina and the general circulation.3

Photoreceptors

Photoreceptors are also known as cones and rods. They are the light-sensing and interpreting cells located within the retina above the retinal pigment epithelium (RPE).

Jaime R. Herndon | January 2019
  1. University of Michigan Kellogg Eye Center. Anatomy of the Eye. 2019. https://www.umkelloggeye.org/conditions-treatments/anatomy-eye Accessed January 6, 2019.
  2. Taggart MS. Retinal pigment epithelium: The eye’s first line of defense against macular degeneration. BrightFocus Foundation website. 2016. https://www.brightfocus.org/macular/news/retinal-pigment-epithelium-eyes-first-line-defense-against-macular Accessed January 6, 2019.
  3. Booij JC, Baas DC, Beisekeeva J, Gorgels TG, Bergen AA. The dynamic nature of Bruch’s membrane. Prog Retin Eye Res. 2010; 29(1): 1-18. Doi: 10.1016/j.preteyeres.2009.08.003 Accessed January 6, 2019.