Low vision is a term for conditions that result in reduced sight and cannot entirely be corrected with eyeglasses, contact lenses, medicines or surgery. Several eye diseases or conditions can cause low vision and here we will discuss the four most common causes of low vision and their risk factors.
Macular Degeneration
Macular degeneration is a disorder that affects the retina, which is the light-sensitive tissue lining the inside of the eye. Within the retina, the area responsible for sharp central vision (called the macula) deteriorates, causing blurred vision. This can cause a blind spot in the central area of vision, which leads to low vision.
There are two types of macular degeneration – non-exudative (dry form) and exudative (wet form). The dry form usually progresses slowly, while the wet form causes more rapid and severe vision loss due to abnormal blood vessels developing under the macula and leak fluid and blood. The biggest risk factor for macular degeneration is age. Age-related macular degeneration most commonly affects adults over 75, and symptoms before age 55 are rare. Other risk factors include genetics, race, smoking, and high blood pressure.
Diabetic Retinopathy
Diabetic retinopathy is a diabetes complication that affects the eyes. High blood sugar levels cause damage to blood vessels in the retina. These blood vessels can swell and leak (called macular edema). Sometimes they close, stopping blood from passing through (called macular ischemia). At first, diabetic retinopathy may cause no symptoms or only mild vision problems. However, over time, it can severely damage the retina, leading to low vision. Anyone who has diabetes can develop diabetic retinopathy. The risk increases for those who have had diabetes longer, as well as those with poor control of blood sugar levels, high blood pressure or cholesterol as well as those who smoke.
Types of Diabetic Retinopathy
- Non-proliferative diabetic retinopathy occurs when leaking blood vessels cause the retina to swell.Â
- Proliferative diabetic retinopathy is caused by new blood vessels growing on the retina’s surface.
Cataracts
A cataract is a clouding of the lens in the eye that affects vision. This clouding can block the light from reaching the retina at the back of the eye, resulting in a general loss of vision. In some cases, a cataract can be surgically removed. Cataract surgery has a high success rate in otherwise healthy eyes but it is not always possible for people who also have other eye diseases. While the risk of cataract increases as you get older, other risk factors include diabetes, smoking, alcohol use, and prolonged exposure to ultraviolet sunlight.
Glaucoma
Glaucoma is a disease that damages your eye’s optic nerve. Most commonly, this occurs when fluid builds up in the front part of your eye which increases the pressure in your eye, damaging the optic nerve. There are four types of glaucoma: open-angle, normal tension, angle-closure, and secondary.
Open-Angle Glaucoma
This progressive eye disease does not have any early warning signs. Patients experience changes to their vision, typically in the side (peripheral), before noticing changes to light perception and issues with their central vision.
Open-eye glaucoma is incurable, but medication can help slow the progression of the disease and improve patient outcomes. Eye drops or draining excess fluid to reduce pressure on the optic nerve are common treatment options.
Laser treatment is also a potential option for patients with this condition. A selective laser trabeculoplasty (SLP) has been shown to successfully treat open-angle glaucoma to the extent that patients did not require eye drops up to three years after surgery. An SLP procedure vaporizes pigmentation in the drainage system that may contribute to fluid buildup; this can lower pressure and be performed repeatedly as it does not require any incisions or burning of tissue.
Normal-Tension Glaucoma
Normal-tension glaucoma is a type of open-angle glaucoma that can lead to eventual blindness. Early intervention and treatment are vital to preserving your eyesight. Patients with normal-tension glaucoma experience symptoms despite their intraocular pressure being within an average range of 12-21mm Hg.
Potential causes of normal-tension glaucoma include disrupted or irregular blood flow to the optic nerve and structural issues with the nerve tissue. Since there are currently no treatments that can directly improve circulation to the optic nerve, traditional open-angle glaucoma treatments are used to manage symptoms.
Closed-Angle Glaucoma
Patients with angle-closure or closed-angle glaucoma often have bulging irises due to partially or completely blocked drainage. As eye pressure increases, the eye begins to bulge, and vision becomes distorted.
The first line of treatment for closed-angle glaucoma is a surgical procedure called a laser iridotomy. During this procedure, your ophthalmologist creates an extremely small hole in the iris to open the angle, allowing for improved drainage of eye fluid.
Patients can develop closed-angle glaucoma suddenly or over time. Symptoms can include redness and eye irritation, intense eye pain, reduced vision, seeing halos of light around objects, headaches, nausea, and vomiting.
Secondary Glaucoma
Secondary glaucoma is caused by another physical condition, such as an eye injury, diabetes, cataracts, or side effects of certain medications. It can be open-angle or closed-angle, and treating it requires first identifying the underlying cause.
Medications, laser surgery, or conventional glaucoma surgery may be effective, but the right solution depends on your unique circumstances. Examples of secondary glaucoma include:
- Exfoliative glaucoma occurs when a piece of dandruff-like material falls into the eye from the outer layer of the lens. It becomes lodged between the cornea and iris, which can lead to blockages and fluid buildup.
- Traumatic glaucoma stems from an eye injury that damages the optic nerve or angle; blunt injuries, such as being hit in the eye, or injuries that penetrate the eye can lead to glaucoma developing rapidly or over time.
- Uveitic glaucoma develops when the middle layer of the eye (uvea) swells. Because the uvea provides most of the blood to the optic nerve, inflammation can cause blockages that lead to increased eye pressure and vision loss.
There are many risk factors for glaucoma, but those over 40 who have a family history of glaucoma should always have regular eye exams to check for glaucoma. In addition, you could be at an increased risk if your eye doctor has noted that you have high eye pressure, are farsighted or nearsighted, have thin corneas, thinning of the optic nerve, or have had an eye injury. Finally, certain health problems can cause glaucoma, such as diabetes, migraines, high blood pressure, or poor blood circulation.
How To Prevent Low Vision From These Diseases
Even though age and genetics play a part, you may have noticed some common risk factors – diabetes, smoking, and high blood pressure, which are all within your control.
Here are the most important steps you can take to reduce your risk of low vision from macular degeneration, diabetic retinopathy, cataracts, and glaucoma.
- Be aware of your family's health history
- Get regular physicals
- Move your body
- Eat a healthy diet
- Don't smoke
- Check out changes in vision with your eye doctor
- Protect your eyes from the sun
- Get your eyes checked at least every two years
By understanding the diseases that cause low vision, you can take steps now to reduce modifiable risk factors or get an early diagnosis to preserve your eyesight.
