Glaucoma is the second greatest factor leading to permanent blindness in the United States. The aqueous humor is a water-like fluid that occupies the anterior chamber of the eye where the pupil, lens, iris, and cornea are located.
The fluid provides the eye with nutrients and the necessary pressure to help maintain the shape of the eye, known as intraocular pressure (IOP). Glaucoma is generally caused by an increase in IOP, which subsequently damages the nerve fibers of the retina and the optic nerve.
The development of glaucoma can be asymptomatic as the condition tends to progress gradually. However, in some cases, the condition can progress rapidly, causing the following symptoms:
- Blurry vision
- Nausea and emesis
- Severe eye pain
- Tenderness in the surrounding areas of the eye
- Reddening of the eye(s)
- Seeing halos around lights
Individuals from Asian, African or Caribbean backgrounds are at more risk of developing the condition as well as those whose parents or siblings have also be diagnosed with the condition. Furthermore, the prevalence of glaucoma typically increases with age and is more common amongst individuals with long-sightedness or short-sightedness, and with medical conditions such as diabetes.
Cataracts are characterized by cloudy patches of the eye’s lens. As the condition progresses, the patching typically increases in size resulting in misty or blurry vision and potentially, blindness. The condition is usually seen in both eyes. However, the rate of progression may differ between eyes, meaning a cataract may not develop in both eyes at the same time.
Common symptoms of a cataract include:
- Perceiving colors to be faded
- Difficulty seeing in low light
- Finding lights glaring or too bright
- Blurry or misty vision
Pain may be experienced if the cataract is in an advanced stage of progression, or if there is another comorbid ocular condition.
Like glaucoma, cataracts are commonly found in older adults. However, they may be seen in young children or babies. Other risk factors include parents or siblings being diagnosed with the condition, prolonged use of steroids, smoking, excessive drinking, and medical conditions such as diabetes.
Diabetic retinopathy is a complication of diabetes. The condition develops as a result of high levels of blood sugar which damages the retina. If left untreated or if not diagnosed, it can result in blindness.
Early-stage diabetic retinopathy tends to be asymptomatic. Early signs of the condition can be detected through routine eye tests.
Those with type 1 and type 2 diabetes are at risk of diabetic retinopathy. However, specific risk factors may increase the likelihood of developing the condition, including:
- Being from an Asian, Caribbean or African ethnic background
- Being pregnant
- Having high blood pressure and cholesterol
- Having diabetes for a long period
- High, persistent blood glucose levels
Myopia (short-sightedness) and hyperopia (long-sightedness) are common refractive errors. Individuals diagnosed with myopia often have difficulty viewing distant objects.
Distant objects appear blurred. In contrast, those with hyperopia can see these objects, yet, close objects appear blurry. Both conditions can range in severity and are common in both adults and children.
Refractive errors can cause headaches, squinting due to eyestrain, dual vision and seeing halos around bright lights.
Myopia tends to run in families. Therefore, you’re at risk of developing the condition if one or both of your parents are short-sighted. Further risk factors include spending prolonged periods focusing on close objects such as reading and not spending enough time outdoors.
Eye Diseases that Can Cause Legal Blindness
Types of Blindness
The greatest fear many patients with eye disease have is “going blind.” Preventing or slowing down the process that leads to losing vision starts with understanding what can cause blindness and what the available treatments are.
Vision impairment is defined as having less than normal vision.
Absolute blindness, defined as having “no light perception,” is rare. When someone has absolute blindness, that person can’t tell the difference between light and dark, even when a bright light is shined into the eyes. Assistance from the government and foundations is available for persons living with this degree of blindness.
By contrast, legal blindness is defined in the United States as visual acuity that is best corrected (with glasses) at 20/200 or less in the better eye, and/or a visual field of 20 degrees or less. Legally blind patients qualify for benefits from the government. People with legal blindness may still have some usable vision.
Legal blindness can be caused by several eye diseases, which we explain in more detail below:
- Age-related macular degeneration (AMD)
- Retinitis pigmentosa
- Diabetic retinopathy
Rare genetic diseases affecting the retina can also cause legal blindness. For example, retinitis pigmentosa can cause “tunnel vision,” in which only a tiny window of central vision remains. Such patients might be able to read 20/20 size letters, but would be legally blind because of the small visual field. Retinal gene therapy developed at the Scheie Eye Institute at the University of Pennsylvania has recently been FDA approved for one form of the hereditary retinal disease called Leber’s congenital amaurosis. The treatment works by injecting normal copies of the RPE65 gene into the retinas of patients born with mutations in this gene. It is expected that additional research will lead to gene therapy for other forms of hereditary and acquired eye diseases.
Thyroid eye disease
Thyroid eye disease (TED) is an eye condition that causes the muscles and soft tissues in and around your eye socket to swell. TED usually happens when you have a problem with your thyroid gland.
TED may also be called thyroid associated ophthalmopathy (TAO), thyroid orbitopathy, Graves’ orbitopathy or Graves’ ophthalmopathy (GO).
The period of inflammation and swelling caused by TED is known as the “active” stage. This generally resolves on its own over a period of about six months to two years. After this, the inflammation settles, and this is known as the “inactive” or “burnt out” stage.
How can TED affect my eyes?
The most common way TED affects the eyes is by causing symptoms of dry eye – watering, grittiness, and soreness. You may also find that bright lights are uncomfortable.
TED can also cause some changes to the appearance of your eyes, and in some cases, to your vision:
- Your eyelids can become puffy and red (lid swelling), which is often more obvious in the morning.
- Your upper eyelid can rise to a higher position than normal, known as eyelid retraction. This can make more of the white of your eye visible, giving a “staring” appearance.
- The soft tissues behind your eyeball can swell, pushing your eyes forward so that they “bulge” (called “exophthalmos”, or “proptosis”).
- Your orbits (eye sockets) may become painful, particularly when your eyes move.
- The muscles that move the eyeball can become swollen which can cause double vision (diplopia).
- If the pressure inside your eye sockets increases, it can squash (compress) the optic nerve, which can cause blurring or dimming of your vision. Very few people with TED experience this, but it’s important to get medical attention straight away if you notice these changes to your vision.
Most people only get a mild form of TED. You may have dry eye which can be managed easily with lubricating eye drops. You may have some eyelid retraction or exophthalmos and any double vision you have may come and go and not cause too much difficulty.
Another retinal disease that can cause legal blindness is diabetic retinopathy. Patients with diabetes can lose vision from swelling or bleeding in the retina, or from retinal detachment. Diabetics can decrease their risk of legal blindness with good blood sugar and blood pressure control and annual eye exams.