What is a Retina?
The word “retina” means “net-like”. When light enters the eye, it passes through the tears, cornea (the clear dome over the iris – the color part of the eye), the pupil (the black dot in the center of the iris which is actually a hole for light to enter into the eye), through the crystalline lens, the vitreous gel, and ultimately onto the RETINA.
The retina lines the entire inside portion of the back of the globe of the eye, and it has blood vessels that course through it to give it a “net-like” appearance, hence its name. The retina has about 125 million light receiving cells, called photoreceptors, that interpret the light that enters the eye and allows us to see.
The Retina’s Role in Eyesight
Our retina is used to detect the zone of the electromagnetic spectrum called the visible spectrum with cells called photoreceptors. The visible spectrum wavelengths that our retina can detect ranges from 380 nanometers to 700 nanometers. Light wavelengths immediately smaller than 380 nanometers are considered to be ultraviolet (UV), and wavelengths immediately larger than 700 are considered to be infrared. Our human retinas can not detect light wavelengths that are UV or infrared.
The majority of the retina does not even determine a specific color of light, and is receptive to various intensities of light or motion. These photoreceptor cells that are responsive to visible light or motion are called “rods” because of their rod-shape appearance. Rods allow us to see light around our central vision – this “edge” of our vision is called our peripheral vision.
There is also a specific zone of the retina aligned directly behind the pupil called the macula which is responsible for our central vision where sharper color perceiving photoreceptor cells, called cones, are focalized. Cones have a cone-shaped appearance, and each cone is responsive to only one color of light: Blue cones are stimulated by blue wavelengths of light, Red cones-redlight, Green cones-green light.
The most densely populated cone area of the macula is the fovea, which is the very center of the macula. In the peripheral retina, the ratio of photoreceptors to nerves is high, whereas in the fovea it can be as low as 1:1. This low ratio allows for our sharpest, fine tuned vision in the fovea that becomes less fine tuned the further away from the fovea and macula that light is received.
How do Contact Lenses Work with the Retina?
For our best vision, light must focus at the fovea location of the retina. When an eye doctor is fine tuning your prescription glasses or contact lenses, they are trying to focus light directly on the fovea.
Your prescription is a measurement in diopters of how far the off-focus point in your eye must be moved to focus light directly on the fovea. Contact lenses are designed to correct these off-focus points, called refractive errors, ensuring that light entering the eye is ultimately focused directly on the fovea. A well-fitted contact lens ensures that the image is sharply focused onto the retina’s fovea, providing clear central vision.
Common Vision Conditions that Involve the Retina
- Retinal Detachment: When a hole develops in the retina, usually from the vitreous gel pulling away from the retina and taking a piece of the retina with it (aka: Retinal Tear), fluid can leak under the retina membrane. The fluid often quickly occupies the space under the retina and lifts it out of position. Since the retina is out of position, vision loss can occur depending on how much of the retina pulls away. If left untreated, the retina can completely detach and lead to complete blindness. Therefore, retina detachment needs to be identified and treated as soon as possible.
- Diabetic Retinopathy/Maculopathy: Diabetes is a vascular disease that affects blood vessels throughout the body. Blood vessels carry oxygen and nutrients within the blood to the retina, macula, and fovea. When diabetes is left uncontrolled, damage to these blood vessels can cause fluid leakage and loss of oxygen support across the entire retina, which can compromise vision to varying degrees and lead to bleeding within the eye.
- Macular Hole: When damage occurs from inflammation, UV damage, trauma, or vitreomacular traction, a hole can develop in the macula that usually includes the fovea. Since the fovea is an area of our most detailed vision, a hole in it can greatly reduce vision.
- Macular Degeneration: Since the macula contains our central vision and the fovea, when the macula degenerates, the risk of the fovea degenerating or experiencing damage also exists. The damage associated with macular degeneration overall leads to a potential loss of central vision in varying degrees.
- Glaucoma: Though glaucoma is more known for peripheral retinal vision loss due to damage at the ganglion cells (the cell bodies of the nerves that connect the photoreceptors to the brain) and is associated with high ocular pressures, it can also affect our central vision even at normal ocular pressures. Recent acknowledgement of the macula being affected in early stages of glaucoma is advancing our understanding of treatment of glaucoma. The greatest impact to vision loss from glaucoma usually occurs when the fovea is affected.
Tips for Maintaining Eye Health of the Retina
- Regular Optometric/Ophthalmic Eye Exams: Get your eyes tested regularly from a professional who specializes in the eye. Since the retina contains all of the light receiving cells, it is important to check it routinely with your eye doctor at every eye exam.
- Sunglasses/UV blocking contact lenses: Ultraviolet light is associated with advancing conditions such as macular degeneration.
- Diet: Maintaining a balanced nutritional diet, especially one that is rich in antioxidants (such as green leafy vegetables) and omega 3 (such as fish) are known to promote retinal health.
- Avoid Smoking: Overall, smoking decreases health and increases oxidants, therefore, increases the risk of eye conditions, including macular degeneration.
- Physical fitness: The eyes are part of the body, so it is important to maintain overall health to maintain healthy eyes. (Healthy Body = Healthy Eyes)
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