The 10 Most Common Eye Diseases

Eye diseases affect 2.2 billion people worldwide. Most of them are associated with age or other diseases, such as diabetes. Find out more!

Written and verified by el biólogo Samuel Antonio Sánchez Amador.

Last update: 07 July, 2023

The sense of sight is one of the most developed in human beings. Thanks to the eyes, we’re able to capture and interpret light, color, shape, distance, position, and movement of everything around us at the brain level. Unfortunately, there are certain common eye diseases that prevent correct vision or make it completely impossible.

The eyes are extremely complex structures that wear out over time, and visual problems can occur at the tissue level, the nerves that communicate with the brain, the ability to drain fluids, and much more. Virtually every human being who lives long enough will develop an eye disease throughout their life, as indicated by the World Health Organization (WHO).

In any case, not all ocular conditions translate into blindness and many of them can be prevented with the appropriate social health system and a healthy lifestyle. If you want to know the 10 most common eye diseases and their peculiarities, keep reading.

The global situation of eye diseases

Before entering fully into the diseases of the sense of sight, we find it interesting to frame this group of clinical pictures at a global level. Various WHO fact sheets help us provide you with the following key information:

• Worldwide, at least 2.2 billion people live with some form of visual impairment or total blindness. Among all the cases, at least 1 billion of them could have been prevented with proper healthcare.
• In the United States alone, 4.2 million people over the age of 40 are totally blind or have severely impaired vision.
• The majority of people with low vision around the world are over 50 years old.
• The prevalence of visual diseases is increasing. By working indoors and near screens, humans strain our eyes more and more and our eyes wear out sooner.

In addition to these data of great interest, it’s important to note that refractive errors and cataracts are the leading causes of visual impairment worldwide. Myopia and presbyopia alone are estimated to cause production losses estimated at more than US $ 200 billion.

The 10 most common eye diseases

The magnitude of blindness and visual impairment is on the rise. Besides refractive errors due to visual effort, diseases such as diabetes (increasingly common) promote retinopathy, among many other conditions. Therefore, it’s important for everyone to know what the 10 most common eye diseases in the world are and how to detect them before it’s too late.

1. Refractive errors

We begin with the group of most famous diseases in the world as far as the visual apparatus is concerned. As indicated by the United States National Library of Medicine, refractive errors occur when the image is improperly focused on the retina of the eye, which causes a marked decrease in visual acuity.

Refractive errors are the leading cause of vision loss worldwide, as 43% of such pictures are explained by one of them. Next, we’ll dedicate a few lines to each of the diseases within this very important group.

1.1 Myopia

Myopia is a refractive error that occurs when the patient perceives distant objects as blurry. In this case, light rays converge in front of the retina, instead of directly on it, so focusing takes place incorrectly. This error occurs when there’s a discrepancy between the ability to focus and the length of the eye.

As indicated by the Mexican Journal of Ophthalmology, in 2015 more than 300 million people were myopic. By 2050, the number is estimated to increase to more than 4 billion patients. Interestingly, the prevalences are very uneven around the world: Walues of 6.1% in Africa and 96.5% in Korea make this clear.

1.2 Hyperopia

In this case, the light rays strike and focus behind the retina, but not on it. Farsightedness can be due to poor focusing ability, an eyeball that’s too small, or both at the same time. Patients with this refractive error have difficulty seeing objects up close.

1.3 Presbyopia

Presbyopia is the gradual loss of the eyes’ ability to focus on nearby objects. It’s a natural part of human aging: It begins at 40-45 years and progressively worsens until the age of 65. For this reason, most elderly people need glasses to read up close.

At a pathological level, presbyopia is caused by a hardening of the lens of the eye associated with senescence. In patients over 40 years of age, the prevalence reaches 60%. From the age of 60, 80% of the world’s population needs to wear glasses, either because of this or another refractive error.

1.4 Astigmatism

In the case of astigmatism, the cornea of the ocular apparatus is poorly curved. This abnormal curvature causes vision to be out of focus, and unlike the rest of the eye diseases mentioned, most patients who experience it manifest their symptoms from birth. It often occurs in conjunction with myopia and hyperopia.

Refractive errors reach astronomical figures, and an increasing percentage of the population suffers from them. These conditions can be solved with glasses, contact lenses, or specific operations, but unfortunately, in low-income countries, many people can’t afford any of these solutions.

2. Cataracts

As the Mayo Clinic indicates, a cataract is an opacity of the normal transparency of the eye lens. Simply put, people with this condition feel like they’re seeing through foggy or frosty glass. The cloudy vision caused by this condition makes many common tasks difficult, such as reading, driving, or recognizing other people.

The transmission of light through the ocular apparatus decreases with age for 2 main reasons: The degeneration of the lens cells and the decrease in the transport of fluids in the tissues of this structure. For this reason, the most common cause of cataracts is simply aging. Today, some 22 million people over 40 years of age develop this clinical picture.

Besides the passing of time, hypertension and diabetes can promote lens degeneration. An injury to the eye, exposure to ultraviolet radiation, genetic predisposition, and the use of addictive substances (such as tobacco) also cause cataracts to appear before their time.

3. Glaucoma

Glaucoma is known in general society as “the silent disease”, as it gradually steals the patient’s sight without them realizing it. In a normal situation, the ciliary body of the eye produces a characteristic fluid, known as aqueous humor. This is released through the ocular drainage system, thus maintaining a correct intraocular pressure (IOP).

In glaucoma, the drainage system of the eye doesn’t work properly and the aqueous humor is stored. This results in higher intraocular pressure, which in turn causes irreversible damage to the optic nerve. As indicated by the Glaucoma.org portal , normal IOP ranges between 12 and 22 millimeters of mercury. Above the upper limit, you’re at risk for glaucoma.

The current prevalence of glaucoma in the world is 60 million affected people, of which more than 8 million are blind. There are 2 main types within this pathological group:

1. Open-angle glaucoma: Evolution is slow and doesn’t appear with apparent symptoms. Even so, it causes a progressive and irreversible deterioration of the optic nerve.
2. Closed-angle glaucoma: Occurs acutely and with very intense pain. It’s accompanied by dilated pupils, nausea, and vomiting.

4. Conjunctivitis

The term “conjunctivitis” refers to inflammation and infection (or both) of the conjunctiva, a mucous membrane that covers the back of the eyelids and the front of the eyeball. One of its most common symptoms is redness of the sclera, due to the high vascularity of the affected tissue.

The Centers for Disease Control and Prevention cite the following most common triggers for conjunctivitis:

• Viral diseases: Some adenovirus or the cause of herpes zoster can cause viral conjunctivitis.
• Bacterial infections: Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Chlamydia trachomatis, and Neisseria gonorrhoeae are capable of causing infections in the eye tissue.
• Exposure to allergens: Allergens are apparently harmless substances that are recognized as pathogenic by the immune system. Conjunctivitis can appear as a symptom of an allergic condition.
• Less common but possible causes: Chemical exposure, contact lens wear, foreign bodies in the eye, contamination, fungal infections, and parasites.

Artificial tears and the use of cold compresses often help alleviate the symptoms of conjunctivitis. The allergic variant is the most common of all, as it affects 15 to 40% of the population at certain times of the year, especially in spring and summer.

5. Diabetic retinopathy

Diabetic retinopathy is a complication of diabetes that affects the ocular system. Although this condition isn’t well known, the journal Elsevier Primary Care highlights that this complication of diabetes is the cause of 2.6% of global cases of blindness.

In short, this condition occurs due to the deterioration of the blood vessels that supply the retina associated with the diabetic picture. It affects 80% of people who have had diabetes for 20 years or more. In the United States, diabetic retinopathy causes 12% of new blindness cases annually and is the leading cause of blindness in people between the ages of 20 and 64.

6. Trachoma

This is perhaps this is one of the most common eye diseases, but fewer people know about it. Trachoma is an eye infection caused by the microorganism Chlamydia trachomatis. Besides being an eye disease, this intracellular bacterium causes genital infections and pneumonia in humans.

As indicated by the WHO, this type of infection is a very significant public health problem in 37 different countries and causes blindness or visual impairment in almost 2 million people. What’s more, an estimated 142 million inhabitants live in areas where trachoma is endemic and are at risk of going blind.

The problem with trachoma isn’t its sporadic appearance. Rather, constant infections damage the eye to the point of causing irreparable blindness. The picture is aggravated when the patient presents trichiasis, where eyelashes grow inward toward the eye. In the end, the eyelashes themselves contribute to the destruction of eye tissue.

7. Age-related macular degeneration

As its name suggests, age-related macular degeneration (AMD) is a disease that’s linked to normal aging in humans. In this condition, the patient’s central vision is gradually destroyed and detail is lost in image recognition. It’s much more common in people over the age of 60.

As indicated by the United States National Library of Medicine, AMD can come in 2 variants:

1. Dry AMD: In this variant, the blood vessels under the macula become thin and fragile. In addition, yellow deposits occur in the tissue, known as drusen.
2. Wet AMD: This variant is much less common, representing only 10% of patients with macular degeneration. In it, new blood vessels grow under the macula that end up breaking and causing the infiltration of fluids. Wet AMD is more aggressive than dry.

The combined prevalence of macular degeneration is 0.34% in the general population. In any case, between the ages of 75 and 84, the probability of developing it increases to more than 15%. Without a doubt, this is another of the most common eye diseases associated with old age.

A world of diseases right under our eyes

In total, we’ve shown you 10 very common eye diseases in general society (4 refractive errors and 6 separate conditions). Most are associated with age, but for example, trachoma is almost exclusive to low-income countries where there’s a lack of access to proper hygiene and a good healthcare system. To a certain extent, having good eyesight is a matter of class.

We’ll close this article with one of the statistics provided at the beginning: Of the 2.2 billion worldwide cases of vision loss, 1 billion of them could have been prevented with proper healthcare. In a way, we’re lucky to be able to wear glasses if we’re diagnosed with myopia or eye drops if we have conjunctivitis.