Our eyes are remarkable things. These small, gelatinous orbs are quite literally our windows to the world. The parts of your eye all work together to paint a picture in our brains of the world around us. The individual parts of the eyeball are each amazing in their design and ability. Together, they enable the wondrous sense of sight. This article will give you an overview of the different parts of the human eyeball and an understanding of the function of each part of the human eye, as well as basic eye maintenance. Keeping your eyes healthy will allow you to maintain your precious vision so you can appreciate the beauty of the world around you.

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Parts of the Eyeball

Parts of the eyeIris

The iris is the colored part of your eye. It is what makes blue-eyed people have blue eyes and brown-eyed have brown eyes. The color of your iris is determined by genetics and heredity and it has no bearing on the functionality of this part of the human eye. The circular iris, however, has the important job of controlling the size of the pupil, and thus, how much light enters the eyeball.

To do this, the iris has a fine, thin membrane that connects to a sphincter muscle. The sphincter muscle opens and constricts the pupil in a proportional circle, so your pupil and iris are always in the shape of a circle, no matter how far open the pupil is.

The function of the iris is often compared to that of a camera’s shutter. It ‘reads’ the amount of light and adjusts accordingly to allow the appropriate amount of light in through the eye’s pupil. To carry the camera analogy further, the shutter function of the iris is responsible for the aperture opening of the pupil.


The black circle in the center of the iris is the pupil. The pupil only appears to be black. Light entering the pupil opening is absorbed by the eye’s tissue, projecting a black-looking dot. The pupil is the part of the eye that permits light to enter the eye, making vision possible. With help from the iris, the pupil is adjustable. The amount of light that is permitted in can range in intensity and the iris and pupil work together to determine just how much light is needed for optimal sight. They then make adjustments to meet that amount.

The size of the pupil opening corresponds to the amount of light that the eye needs. In darkness, the pupil can open to a maximum width of between 3 to 8 millimeters, depending upon the individual. But in bright light, the pupil opening can close to 2 to 4 millimeters. Because one function of the pupil is to focus the light to the cornea, when the opening of the pupil is smaller, the image being projected is sharper and clearer. A pupil that opens wide to allow the maximum amount of light to enter sacrifices some sharpness of the image in order to be able to see the overall image.

Light is not the only contributing factor to the size of the pupil. Age can also impact the pupil. The pupils of younger people have the ability to open wider than those of older people. Some drugs or medications, such as opioids, make the pupils smaller, while other drugs, including cocaine, amphetamines, and psychedelic mushrooms, have the opposite effect. They make the pupils appear larger. Lastly, pupils can reflect mood or feelings. If you are looking at someone you love or are attracted to, your pupils will open wider.

The opening and closing of the pupils is an involuntary reflex, known as the papillary light reflex. Therefore, it can be used as an indicator of brainstem function. This is why you will see TV doctors shine a small penlight into the eyes of injured or unconscious patients. They are mimicking what actual physicians do. If the patient’s pupils constrict in the bright light, it is a sign that the brain is fully functioning.


The cornea is the clear, rounded covering over the iris and pupil. This part of the eye has a dual function. First, it protects the eye and the pupil opening from hazardous materials, such as dust, dirt, germs, and bacteria. Additionally, the cornea filters out the harmful ultraviolet waves in natural sunlight that could damage our sensitive eyeballs. Because the cornea is the first line of defense for the eyeball, this part of the human eye is more susceptible to injury and disease.

The cornea also serves as a lens that bends and focuses the light that enters the eyeball. In fact, as much as three-fourths of the eye’s ability to focus is controlled by the cornea. The cornea works with the eye’s lens to bend and refract incoming light and aim it to the retina so that the image appears.

The cornea is smooth and moist, thanks to the tear ducts, and allows the eyelid to easily cover the eyeball, as fast as a blink.


The lens is the part of the eye that bends the incoming rays of light to depict the image on the retina. The lenses are located behind the irises and are transparent, so you cannot see them, yet their role is vital. The lenses help to bring the image into sharp focus by contorting. A thicker, fatter lens will bring near objects into clearer focus, while a flatter, thinner lens shows objects that are further away.


If the iris is like a camera’s shutter and the pupil is the camera’s aperture, then the part of the eyeball that is most like the film would be the retina. The retina is located at the back of the eye and receives that light that has been focused toward it by the cornea and the lenses. The retina is a thin, light-sensitive, photoreceptor membrane that collects the light…and the information about the image that is contained in the light…and sends that data to the brain via the optic nerve.

The retina is affixed to the back of the eyeball, but it can, if damaged, become detached. Retinal detachment, or the movement of the retina from its normal position, causes blindness.


The vitreous is the clear, gelatinous fluid that fills the eyeball. It helps the eye maintain its round, spherical shape and, more importantly, holds the retina in place. The gel-like property of the vitreous is the result of its chemical make-up. Although it is mostly water, it also contains proteins, sugars, and collagen.


The white part of the human eyeball is called the sclera. The sclera is comprised of elastic fibers of collagen that form the opaque orb of the eyeball. The sclera houses the inner workings of the eyeball, including the retina and the vitreous.


The conjunctiva is a thin membrane that protects the inner surfaces of the eyelids by coating them in mucus-like moisture. This part of the eye keeps the eyeball lubricated by spreading tears across the surface of the sclera and by adding moisture via its own mucus membrane.

Optic Nerve

All the parts of your eyeball can work perfectly, but if the optic nerve is damaged, you will not be able to see. The optic nerve takes the coded data that has been received by the retina and transports it to the part of the brain that is responsible for vision. It is in the brain that the information is decoded to show the image that the eyes have seen. Although it is not located in the eyeball, the brain is one of the most important parts of the vision process in that it forms the image from the light that filters into the eyeball.

Maintaining Eye Health

Our eyes do extremely important work, yet they are delicate and fragile. To make sure that all of the parts of your eyes stay in top condition and working properly, there are some basic guidelines to follow.

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Parts of the eyeHave Regular Eye Exams – Schedule yearly eye examinations with an eye care professional. During your exam, your eye doctor should dilate your pupils to be able to view the parts of your eyes and inspect them for signs of disease or damage. Disorders such as glaucoma, macular degeneration, and diabetes may be diagnosed prior to you experiencing any symptoms.

Protect Your Eyes – When you are engaged in activities that could injure your eyes, be sure to wear protective eyewear, such as safety goggles or eye guards. It is not uncommon for people to injure their eyes while playing sports or at the workplace. In fact, chemicals, liquids, and fumes in the workplace can be hazardous to your eyesight. Bright sunlight can also damage your eyes. If you are going to be spending a lot of time outside in the harsh sun, wear a pair of sunglasses that offer UV protection by blocking nearly all of the sun’s harmful UV-A and UV-B waves.

Don’t Smoke – You know that smoking is bad for your heart and lungs, but it is hazardous to your eyes, too. Some eye diseases, including cataracts, optic nerve damage, and macular degeneration, can be exacerbated by smoking. Ideally, you should never take up the smoking habit. But if you are a smoker, you should try to kick the habit, for the sake of your eyes and your overall health.

Guard Against Eye Strain – Eye strain and eye fatigue are common afflictions. Staring at computer screens, televisions, or cell phone screens can increase eye strain which can lead to fatigue and dryness. If your job requires you to sit in front of a computer screen all day, follow the 20-20-20 method for alleviating eye strain. Take your eyes from the screen every 20 minutes and focus on something about 20 feet away from you for at least 20 seconds.

Parts of the eyeEat an Eye-Healthy Diet – Eat a diet that includes plenty of dark green, leafy vegetables, like spinach and kale, along with vegetables high in beta-carotene, including carrots, beets, and sweet potatoes, because these foods are rich in the minerals that have proven to be beneficial for your eyes. Recent research also indicated that salmon, tuna, and other foods that are high in omega-3 fatty acids also promote eye health.

Know Your Risk – Know what your family history is in regard to eye health. Are there family members who have been diagnosed with eye diseases, such as macular degeneration? Many eye disorders are hereditary; therefore you are at an increased risk to also be diagnosed with them if you have one or more family members with an eye disease. Knowing your family’s eye history allows you to discuss this information with your eye care professional so he or she may be on the lookout for early evidence of eye disease during your annual eye exams.

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Maintain Your Weight and Fitness – By maintaining your ideal weight and fitness level, you stave off diseases like diabetes that can rob you of your vision. Obesity has also been linked to glaucoma and other eye-related disorders. Your overall health and fitness impact all parts of your body, including your eyes.

Parts of the eyeClean Your Contact Lenses – If you are a contact lens wearer, take care to avoid infection or eye damage that can come about from contact lens use. Always follow the instructions for contact lens care given to you by your eye care professional. Start by thoroughly washing your hands before you handle your contact lenses. Properly clean and disinfect the lenses and store them in the right solutions when you are not wearing them. It is also important that you follow your eye care professional’s guidelines for wearing the contact lenses. Some contact lenses are meant for extended wear and others should be removed periodically so your eyes can rest. Sleeping in your contact lenses or wearing them too long could cause damage to your corneas.

Understanding the different parts of the eye and how they work together for sight to occur will help you to realize the delicate process of vision. Our eyes provide us with a window to our world. Our eyesight is precious and deserves to be protected.

Dr. Barry

Dr. Barry

December 26, 2018