When it comes to your eyes, you only get two! While corneal transplants and lens exchanges exist, there is currently no replacement for the eye as a whole. Therefore, we need to do our best to take care of what we have.
Ocular Anatomy of Healthy Eyes
To best understand how to keep the eyes healthy, it may be useful to have a basic understanding of the anatomy of the eyes.
The eyes are technically an extension of the brain. This means the eyes are part of the central nervous system—the brain and the spinal cord.
Like the rest of the central nervous system, the eyes are a unique organ. The eyes must remain translucent so that structures do not interfere with the passage of light. This means the entire structure of the eye must be quiet precise and function as a well-oiled machine.
The very front structure of the eye is called the cornea. The cornea is the clear layer that you can touch with your finger, lying in front of the colored part of your eyes (the iris).
The cornea acts as a protective barrier, keeping unwanted debris and bacteria out by trapping the debris in the tears, which are then blinked away via closure of the eyelids.
The cornea also acts as the first refractive surface of the eye—it bends incoming light rays to help focus them on the backmost structure of the eye called the retina.
In the middle of the eye is a structure called the crystalline lens. The lens further refracts light so that it lands on the retina. The lens is flexible, it changes shape based on the object you are looking at (near vs far) to bend light accordingly in a process called accommodation.
When the lens loses its ability to accommodate, it loses its ability to focus on objects in different ranges, and therefore you will notice you can only see clearly at one distance. Most often, people will complain of the inability to view objects close up, resulting in the need for reading glasses. This process is part of the normal aging process and is referred to as “presbyopia”.
The Retina
Saving the best for last, the backmost layer of the eye is the retina. The retina is composed of 10 individual layers which each play a pivotal role in the creation of images.
The retina contains specialized cells called photoreceptors. Photoreceptors detect light, thus activating a cascade of events. Ultimately, the stimulated photoreceptor releases a bioelectric signal that travels from cell-to-cell via axons.
To exit the eye, close to a million axons conglomerate together to create the optic nerve. You can think about this like the hundreds of thousands of fibers making up a fiber optic cable.
Each eye has one optic nerve. The optic nerve extends from the eye to the brain. The signals from stimulated axons reach the occipital cortex in the back of the brain where the signals are processed and transformed into images.
What is also important to note in the retina is an area called the macula. The macula contains the densest area of photoreceptors, making it responsible for our central vision. Above all else, we want to keep the macula healthy and clear of obstructions.
Obstructions can occur when there is direct damage to the cornea, lens, or retina that transforms the normally translucent material opaque. Other possibilities that can interfere with the pathway of light is if blood vessels leak blood or inflammation into the “fillers” of the eye—aqueous humor and vitreous humor.
Aqueous humor is the fluid that fills the anterior half of the eye—the lens to the cornea. The aqueous humor is formed from ultra-filtrated blood to provide nutrition to the anterior half of the eye’s structures.
Aqueous humor is continuously created and enters the eye roughly at the equator, where it then flows forward to eventually be filtered out through special channels (the trabecular meshwork) to meet the venous system and be secreted back into the blood network.
Aqueous humor is therefore responsible for our eye pressure. We want eye pressure to be between about 10 mmHg and 21 mmHg. If the pressure is too high it can compress the structures of the eye leading to permanent damage and therefore vision loss. If the pressure is too low it can cause the eye to wrinkle and fold in on itself in an event called hypotony.
The fluid filling the back half of the eye (the lens to the retina) is called vitreous humor. Vitreous humor is only created one—during fetal development. Vitreous humor is a bit more of a gel consistency that provides nutrients to the developing eyeball. One the eye is completely developed, the vitreous humors’ only role is to provide structural support to the eye.
Anything that interferes with the pathway of light from the cornea to the retina creates an absence of light, which is detected and converted into “blackness” by the brain. Therefore, it is of upmost importance to keep all structures of the eye healthy and clear in order to maintain clear, unaltered vision.
As you can see, this task is more difficult than one may originally think!
5 Tips to Keep Healthy Eyes
#1 First and foremost, the best thing you can do for your eyes is to get yearly eye exams—even if your vision is great.
The only structure that contains nerves that detect pain is the cornea. All the other structures—lens and retina—are nerve-less. This means significant changes may be occurring, but you may not notice them until your vision is reduced, at which point it may be too late to do anything about it.
#2 Wear eye protection such as safety glasses and sunglasses whenever applicable.
While our corneas protect us from small debris like dirt, dust, and bacteria, they cannot protect our eyes from rocks, metals, and other foreign bodies. Whenever you are working on something with small parts (cars, woodworking, machinery, etc.) wear safety glasses to prevent any sharp or high velocity objects from entering your eye.
We do not want these objects to penetrate the cornea, as this will hurt, open the eye up to allow bacteria in (and therefore infections), and can cause scarring. Scarring of the cornea changes the cornea from translucent to opaque. If this occurs across the line of sight, you will have permanently reduced vision.
Sports goggles are a great idea for anyone participating in contact sports such as baseball, basketball, softball, pool, racquetball, pickleball, etc.
Sunglasses are also extremely important forms of eye protection. Excessive UV light from the sun has been linked to cataract formation (clouding of the lens), damage to the retina, and even growth formation (melanoma, pingueculas, pterygiums, etc.).
#3 Take care of your systemic health!
Diabetes, hypertension, high cholesterol, and smoking have all been linked to changes in the blood vasculature system. As noted above, the eye is perfectly made from birth. Any new blood vessel growth, or leaky blood vessels, interfere with vision and can result in permanent vision loss or even blindness if left unchecked.
#4 Regularly eat green leafy vegetables and purple fruits
These superfoods such as kale, spinach, broccoli, blueberries, strawberries, grapes, cherries are rich in antioxidants such a lutein and zeaxanthin.
Antioxidants play a crucial role in keeping the macula healthy. In fact, those diagnosed with macular degeneration are prescribed special eye vitamins that are high in these antioxidants to help slow the progression of the disease.
#5 Take breaks from near work such as computers, reading, and watching TV.
Near work requires stimulation of the accommodative system. The eye has muscles just like every other part of the body—hours of stimulated accommodation is like your eyes lifting weights for hours non-stop!
Too much near work can cause eye-strain, blur, dry eye, and headaches. If you work on computers regularly, blue light blocking glasses may help to reduce some of the strain on the eyes.
Additionally, we recommended the 20-20-20 Rule: every 20 minutes take a 20 second break to look at an object 20 feet away. This allows your accommodation system to relax and refocus for a bit and will hopefully help to decrease symptoms associated with too much near work.
Taking breaks from near work is especially important for children in the developmental years between birth to the age of 7-8 years old. Research has shown that increased time spent doing near work during developmental years has greatly contributed to the myopia crisis (a large increase in the number of individuals who are nearsighted). The best way to prevent this is to encourage children to go outside and play for 2-3 hours each day!
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