Definition of Glaucoma
Glaucoma is a disease of the optic nerve, the major nerve of vision. The optic nerve receives the light-generated nerve impulses from the retina and transmits them to the brain, where they are recognized at vision. Glaucoma is characterized by a unique pattern of progressive damage to the optic nerve, which begins to cause a subtle loss of peripheral (side) vision. It is often, but not always, associated elevated intraocular pressure. It is this elevated eye pressure that leads to damage of the optic nerve. Glaucoma may sometimes occur in the presence of normal eye pressure, which may be due to poor regulation of blood flow to the optic nerve. Glaucoma is often inherited and may not show up until later in life. If glaucoma is not diagnosed and treated, it can progress to permanent loss of central vision and blindness within a few years.
Most people with glaucoma have no early symptoms or pain. Everyone should get their eyes examined by their optometrist, so she can diagnose and treat glaucoma before long-term visual loss occurs. People over the age of 40 who have a family history of glaucoma should get a complete eye exam from an optometrist every year.
Incidence of Glaucoma
People often don’t realize the severity or who is affected by glaucoma. Despite it being a misunderstood disease, glaucoma is the leading cause of irreversible blindness in the world and the second leading cause of blindness in the world, according to the World Health Organization. And, unfortunately, about 10% of people with glaucoma who receive proper treatment still experience vision loss. All ages, from babies to senior citizens, are at risk for developing glaucoma. Even though older people are at a higher risk for developing glaucoma, babies can be born with glaucoma (about 1 out of every 10,000 babies born in the US). It is estimated that over 3 million Americans have glaucoma, but only half of those know they have it, due to the fact that initially there are no symptoms and the subsequent loss of side vision is usually not recognized. More than 120,000 in the US are blind in both eyes from glaucoma and as many as 6 million worldwide, which accounts for 9-12% of all types of blindness. Worldwide, it is estimated that over 60 million people are glaucoma suspects. Blindness from glaucoma is 6-8 times more common in African Americans than Caucasians. Of the 20% of people that know glaucoma is related to elevated eye pressure, most those 20% mistakenly thought people could tell if they had glaucoma by their symptoms, or that it was easily cured and did not lead to blindness.
Anatomy of Glaucoma
In most types of glaucoma, the eye’s drainage system becomes clogged, so the intraocular fluid cannot drain at a normal rate. When the fluid builds up, the pressure within the eye increases. The elevated pressure damages the delicate optic nerve and results in vision loss.
The front of the eye is filled with a clear fluid called aqueous humor, which provides nourishment to the structures in the front of the eye. The ciliary body, which surrounds the lens of the eye, produces the aqueous humor. This fluid flows through the pupil and exits the eye through tiny drainage channels called the trabecular meshwork.
These drainage channels are located at what is called the drainage angle of the eye and is around the outer edge of the iris. (See figure above) The arrow illustrates the flow of the aqueous humor from the ciliary body, through the pupil, and into the trabecular meshwork. The production, flow and drainage of the aqueous humor is an active, continuous process that is needed for proper eye health. The intraocular pressure (or IOP) depends upon the amount of fluid in the eye. If the drainage system is functioning properly, then fluid can drain out and prevent a buildup of fluid pressure. A person’s IOP varies throughout a 24 hour period, but it normally stays within a range that does not damage the eye.
There are millions of nerve fibers that begin at the retina and meet at the optic disc. As fluid pressure increases in the eye, it begins to damage the sensitive nerve fibers causing them to gradually die. When this happens, the optic disc begins to hollow and develop a cupped shape. Elevated eye pressure for too long will damage the optic nerve, resulting in vision loss.
Types of Glaucoma
There are many different types of glaucoma. Most types can be classified as either open-angle glaucomas, which are usually chronic, or closed-angle glaucomas, which occur suddenly or chronically. Most glaucomas affect both eyes, although the disease can progress more rapidly in one eye than in the other. When just one eye has glaucoma, it can be a result of previous injury to the eye, inflammation, or the use of steroids in that eye.
Open Angle Glaucomas
- Primary Open-Angle Glaucoma (POAG)- This is the most common type of glaucoma. It accounts for at least 90% of all glaucoma cases. It’s frequency increases slowly with age and it is a chronic, lifelong disease. It is said to be primary because its cause cannot be attributed to any structural changes in the eye. The trabecular meshwork looks normal, but fluid does not flow out like it should. The drainage angle is wide open and symptoms, as well as, damage are not noticed until the vision loss is advanced.
- Normal or Low Tension Glaucoma– This variant of primary open-angle glaucoma is characterized by progressive optic nerve damage and loss of side vision despite normal intraocular pressures. It is thought to be caused by decreased blood flow to the optic nerve.
- Congenital (Infantile) Glaucoma- This relatively rare, inherited type of open-angle glaucoma is when the drainage system is underdeveloped at birth. The increased pressure of the eye causes vision loss and and enlarged eye. The eye of an infant is more pliable than an adult eye and enlarges due to the elevated eye pressure. Early diagnosis and treatment are critical to prevent vision loss in these children.
- Pigmentary Glaucoma- With this condition, the pigment granules of the iris detach and block the drainage system of the eye. which leads to elevated eye pressure and damage to the optic nerve. This type of glaucoma is more common in younger men.
- Exfoliative Glaucoma- This type of glaucoma can occur with either open or closed-angle glaucoma. It is characterized by deposits of flaky material on the front surface of the crystalline lens that flow into and clog the trabecular meshwork, which raises the eye pressure. This type of glaucoma occurs in any population, but is more prevalent in older people and those of Scandinavian descent. It has recently been associated with hearing loss in older people.
- Traumatic Glaucoma – A blunt trauma to the eye or a penetrating injury can damage the eye’s drainage system, leading to a secondary glaucoma. This type of glaucoma can occur immediately after the injury or even years later. The most common sports-related injuries to the eyes are blunt trauma from baseballs, racquetballs, and boxing gloves.
- Uveitic Glaucoma- An inflammation in the eye, called uveitis, is treated with eye medicine containing steroids. The use of steroids can cause a secondary glaucoma, which is usually treated with glaucoma eye medication and gradually disappears after the course of steroid drops is discontinued.
Angle-closure glaucoma is a less common form of glaucoma, and is caused by blocked drainage channels, where the angle between the iris and the cornea closes, resulting in a sudden rise in intraocular pressure. It develops very quickly and has symptoms and damage that are usually very noticeable. In acute angle-closure glaucoma, the intraocular pressure can elevate very suddenly as the drainage channels are blocked. Sometimes, it occurs when the pupil becomes dilated, which causes the iris to bunch up in the drainage angle. This type of glaucoma is linked with smaller eyes or farsightedness and cataracts. Medications that cause the eye to dilate can also trigger an angle closure. These medications can be found in eye drops, cold remedies, Celexa and other selective serotonin reuptake inhibitors, Topamax, or even seasickness patches. It can also occur in a darkened room or movie theater, where the pupil will dilate to let in more light automatically. For this reason, people with narrow angles are often given eyedrops that keep their pupils small.
Symptoms of an acute angle-closure glaucoma are:
- eye pain
- red eye
- blurry vision
- corneal edema, causing haloes around lights and a cloudy cornea
- the pupil of the eye may be large and nonreactive to light
Treatment for acute angle-closure glaucoma includes oral carbonic anhydrase inhinitors and eye surgery, where the ophthalmologist creates a hole in the iris with a laser to allow the aqueous fluid to drain.
Risk Factors for Glaucoma
Since glaucoma is called the “sneak thief of sight”, where sight can be damaged without any obvious symptoms, it is extremely important for people to be aware of how early detection and treatment can stave off vision loss. While everyone is at risk for glaucoma, certain people and populations are at a much higher risk and should be checked more frequently by their optometrist. The major risk factors for glaucoma include:
- Family history of glaucoma- More than 50% of glaucoma is familial, especially among siblings.
- Age over 45 years- People are six times more likely to get glaucoma if they are over 60 years.
- Black racial ancestry- Glaucoma is 6-8 times more common in those with black ancestry than in caucasians.
- Irish, Russian, Japanese, Hispanic, Inuit or Scandinavian descent
- History of elevated intraocular pressure (IOP)
- Decrease in corneal thickness and rigidity
- History of injury to the eye- a secondary glaucoma can occur immediately or even years later. The most common are baseball or boxing injuries.
- Use of steroids, either in the eye, inhaled, or in oral or injected form
Symptoms of Glaucoma
Most people who develop open-angle glaucoma feel fine and do not notice a change in their vision initially, because glaucoma gradually damages the nerves that affect the side or peripheral vision. By the time a person notices vision loss, the disease is quite advanced. Without proper treatment, blindness can occur. With regular eye exams every 1-2 years, early detectiion and treatment by an optometrist can preserve vision.
How is Glaucoma Diagnosed?
An optometrist will use dilating drops to examine the eyes for glaucoma. She will check the shape and color of the optic nerve, and if there is glaucoma, it will have a certain appearance that changes over time. She may take photographs or imaging of the optic nerve to track the progression of the disease. The eye pressure will be checked with a tonometer. The peripheral vision will be checked with a visual field analyzer to determine if there is any loss of side vision. She will also measure the drainage angle to see if it is wide open or narrow. The thickness of the cornea using a pachymeter is often measured by the optometrist as well.
Diagnosing glaucoma is not often easy, and careful evaluation of the intraocular pressure and optic nerve will continue to be essential for diagnosis and treatment. If the disease is particularly difficult to diagnose or treat, a referral to a glaucoma specialist may be warranted.
Glaucoma is usually treated with medicated eyedrops, although laser and surgery can also be used. Most cases can be controlled with these treatments and continuing research is helping to find better medications, surgical techniques, as well as, further causes of glaucoma.
- Medications – Medicated eyedrops are the most common treatment modality for glaucoma. These drops lower the intraocular pressure by either reducing the fluid formation or helping to open the outflow of fluid. Side effects of these drops may include: irritated eyes, allergies, redness, blurred vision and stinging. Certain classes of glaucoma medications may affect the heart and lungs.
- Laser surgery – A laser procedure can increase the outflow of fluid from the eye for people with open-angle glaucoma. This is called a trabeculoplasty. Laser can also stop fluid blockage if the patient has angle-closure glaucoma. A lasered hole in the iris, called an iridotomy, allows fluid to flow more freely into the drainage area of the eye. Another type of laser treatment is called cyclophotocoagulation, which treats the middle layer of the eye thereby reducing the fluid production.
- Microsurgery – A procedure that creates a new channel to drain the fluid and lower eye pressure is called trabeculectomy. This treatment sometimes needs to be done several times. The ophthalmologist may implant a tube to assist in fluid drainage. As with all eye surgeries, there are risks of infection, bleeding and temporary or permanent vision loss.
People with primary open angle glaucoma are most often treated with a combination of eye medications, laser and microsurgery. Congenital glaucoma patients are treated with surgery, primarily.
What Causes Glaucoma?
Glaucoma is the result of elevated fluid pressure inside the eye causing damage to the optic nerve. This pressure occurs when the liquid in the front part of the eye is not circulated properly or there is too much fluid being produced. Normally, the aqueous humor flows out of the eye through a mesh-like channel, called trabecular meshwork. If this channel gets blocked, pressure builds up, and glaucoma is then diagnosed. This disease often has a hereditary component, so it is important for patients to let their children and grandchildren know about their eye disease. Less common causes of glaucoma include blunt trauma to the eye, a chemical injury to the eye, severe eye infections, blocked blood vessels inside the eye, inflammatory conditions, and even eye surgeries to correct another condition. Glaucoma usually affects both eyes, but is often worse in one eye. The optic nerve is the most susceptible part of the eye to high pressure due to delicate nerve fibers being easily damaged by direct pressure or by decreased blood flow to the nerve. Damage to the optic nerve and loss of vision from glaucoma is irreversible. However, lowering the eye pressure can help preserve the vision remaining. Most people who follow their treatment plan and maintain regular eye exams with their optometrists do not go blind.
Bottomline, diagnosis is the first step to preserving vision. At Visionary Optometry of Modesto, Dr. Kathryn Larsson is skilled at examining the eye and is able to determine if there is a risk for glaucoma. Call us at (209) 526-9883 and make an appointment to get your eyes, or your loved ones eyes checked!