Glaucoma: An Overview

Glaucoma is one of the leading causes of blindness in the United States, and it affects more than 3 million Americans, with only half knowing that they even have it. Glaucoma is a general term for a family of eye diseases that damages the optic nerve, which will cause a partial or complete loss of vision as it progresses. The optic nerve connects the eyes to the brain allowing us to process our vision.  When damage occurs to those nerve cells, loss of vision results. Researchers do not fully understand how and why glaucoma occurs, but we do know that there is a strong genetic component. We cannot cure glaucoma, but we can manage it very well.

The key to managing this condition is early detection, compliance with treatment plans, and follow-up. The goal of treatment is for the progression of the disease to be delayed or halted. Most of the time, there are no symptoms of glaucoma, which is unfortunate and is one of the more frightening aspects of this disease. The two things that typically bring a patient to an eye doctor (pain and vision loss) are not experienced with glaucoma, at least in its early stages.

-  Some do not notice any change in their vision until the damage is quite severe.

-  Blind spots develop in your peripheral (side) vision.

-  Blurred vision or halos.

-  Mild headaches or eye pain.

-  Nausea 

-  Vomiting

A comprehensive eye examination is necessary to properly look for findings that can be consistent with glaucoma and to order special testing that will confirm or deny our diagnosis and help your optometrist be able to manage, design a treatment plan, and monitor the progression of your condition.  Glaucoma is often an adjunct finding of a routine vision exam for the purpose of updating a prescription or just what you thought was a simple yearly checkup.  One myth out there that we hear a lot is “my pressure is fine, I don’t have glaucoma.”  Well yes, we do check your eye pressure (intraocular pressure), but that’s really only one piece of the puzzle.  We note the structure and anatomy of your individual eye, including the angle where your cornea and iris meet, the lens and the colored iris for any abnormalities, and the health of the optic nerve head.  This is the end of the nerve that connects the eyeball to the brain and damage that occurs here, called optic neuropathy, is what is responsible for the peripheral vision loss in glaucoma.  All of these aspects of a comprehensive eye exam come together for a potential glaucoma diagnosis.

If your eye doctor is suspicious about glaucoma after examining you with the slit-lamp biomicroscope, he or she may order some additional testing to make a final diagnosis or as baseline data to monitor you for changes in the future.  An automated visual field may be ordered to determine if any peripheral vision defects consistent with glaucoma can be picked up.  Gonioscopy uses a special lens to view the angle of the eye, an area that is difficult to see on normal examination.  Viewing the angle can give us insight into how well the drainage system of the eye might be working or if it is clogged up like the sink in your bathroom.  Pachymetry measures the thickness of the cornea and helps a practitioner be better able to interpret IOP measurements initially and in the future.  Finally one of the most helpful tools we have in our toolbox is optical coherence tomography, known as OCT.  This uses light waves to take cross-section pictures of the retina and allows an optometrist to map and measure the thickness of the retina’s distinctive layers.  An OCT has sometimes been called an MRI of the eye for the detail it shows.   All of these special testing procedures will influence a doctor’s decision on whether to begin treatment and what kind, wait and watch closely, and/or what kind of followup schedule will be appropriate.

According to the Glaucoma Research Foundation (GRF) there are multiple kinds of glaucoma which will discuss here.

1.  Primary Open Angle Glaucoma (POAG).

2.  Angle Closure Glaucoma.

3.  Normal Tension Glaucoma.

4.  Congenital Glaucoma.

5.  Pigmentary Glaucoma.

6.  Pseudoexfoliative Glaucoma.

7.   Traumatic Glaucoma.

8.  Iridocorneal Endothelial Syndrome (ICE).

9.  Uveitic Glaucoma.

This is the most common form of glaucoma accounting for up to 90% of all glaucoma cases and affects about 3 million Americans according to the GRF.  ‘Open angle’ refers to the space of the eye where the cornea meets the iris which should be wide and open to fluid drainage.  It is associated with an elevated eye pressure (intraocular pressure or IOP) and usually develops slowly.  This elevated pressure in the eye gradually causes damage to the cells of the optic nerve and results in irreversible vision loss. The condition is something a patient will have to attend to their entire life.

Although much more rare, angle closure develops very quickly and is considered an ocular emergency. This is caused by an extremely narrow or closed angle between the cornea and the iris. A closed angle causes drainage ducts in the eye to become blocked, leading to a sudden spike in intraocular pressure, which in turn will cause irreversible damage to the nerve very quickly.

This type of glaucoma is not as fully understood.  It involves damage to the optic nerve, however intraocular pressure is almost normal levels.  In general, a normal pressure range is between 12 - 22 mm Hg.  For some reasons, it seems the the optic nerve is more susceptible to damage even under a normal amount of eye pressure.  Family history plays an important role and people of Japanese ancestry seem to have a higher risk of developing this condition.  Other risk factors include ischemic vascular disorders, systemic hypotension, and abnormal blood coagulation.  Newer studies have suggested a connection with obstructive sleep apnea syndrome which may compromise optic nerve head blood profusion.

This is also referred to as pediatric or infantile glaucoma and is usually diagnosed within the first year of life.  It occurs because of poor development of the drainage structures in the eye.  Often surgery is recommended to correct any issues with ocular anatomy and sometimes medication in the form of eye drops can still be necessary.  Parents may notice unusually large eyes in their baby or excessive tearing, extreme light sensitivity and a hazy or cloudy look to their eyes.  A young child should be seen by a pediatric glaucoma specialist as soon as possible.

Pigmentary dispersion syndrome occurs when pigment from the back of the iris flakes off into the clear fluid that fills the front of the eye, called the aqueous humor.  Natural currents in this fluid carries the pigment granules towards the drainage ducts in the eye, clogging the ducts like a bathtub drain.  This results in an increase in eye pressure.  The rise in intraocular pressure can cause damage to the optic nerve.  Seeing a trend here?  If damage occurs to the optic nerve, we classify it as pigmentary glaucoma.  An interesting point to note is that some studies have found a connection between vigorous exercise such as running or contact sports and more pigment being released from the iris, possibly worsening the condition.

Pseudoexfoliation is a result of accumulation of protein in the drainage system, which again blocks the outflow of fluid. It can also build up on the edge of the pupil, the lens, and the zonules that hold the lens in place. This is a case of what can be fast progression of glaucoma and may need more frequent followup visits. This accumulation of flaky protein can occur in other parts of the body as well, but primarily in the eyes. There is a high prevalence of this condition in Scandinavian countries and Mediterranean populations, as well as Russians, and Indians and it has been recently connected to a gene anomaly.

Traumatic glaucoma can be result of any kind of trauma to the eye, including blunt force trauma penetrating injuries, or even ocular surgery.  It can be set off immediately after the injury or even years later.  So regular followup care is extremely important following any ocular trauma.  Blunt force trauma is common with sports-related injuries and can cause damage to the fluid drainage system and can also cause a “clog” in the system from the blood, debris, plasma, and pigment that may have accumulated due to the original injury.   Glaucoma can be a result from a penetrating wound or open globe injury as well.  Eye pressure is often low when the injury first occurs, however once the wound is repaired, the area can become swollen, irritated, and excessive bleeding can cause IOP to rise once again.

This is a group of diseases or conditions that can lead to glaucoma, all of which have some clinical signs in common.  The innermost layer of the cornea, called the endothelium, functions as a pump to keep fluid in the cornea at normal levels which keeps the tissue clear and non edematous.  In ICE syndrome, the pumps do not function well and the cornea can become cloudy.  These abnormal cells of the corneal endothelium can replicate and move to areas where they do not belong, including the angle, which clogs up the drain of the eye, and the iris, which can cause the tissue to stretch or tissue to clump into Cogan-Reese nodules.  ICE gets its name from these clinical abnormalities.

Iris nevus/Cogan Reese nodules

Chandler Syndrome

Essential/progressive iris atrophy

Uveitis is an ocular inflammatory condition that can occur for a variety of reasons some of which include autoimmune conditions, Posner-Schlossman Syndrome, Juvenile Idiopathic Arthritis, and sarcoidosis. Unfortunately glaucoma can result in up to 20% of these patients that experience uveitis, especially recurrently.  The connection between uveitis and glaucoma is complex.  The inflammatory debris that occurs in uveitis obstructs the drainage system like a dirty air filter, resulting in decreased outflow through the trabecular meshwork and raising IOP.  Longer term complications include scar tissue created by the inflammation that can further obstruct outflow.

While we cannot cure glaucoma, we can manage it very well, especially if diagnosed in its earlier stages.  Your optometrist and sometimes your ophthalmologist (an eye surgeon) will work together to determine the best course of treatment for your individual presentation of the disease.  We will discuss medication therapy, laser procedures, and surgical option in depth below. 

Medical therapy includes prescription eye drops that lower the eye pressure inside the eye are usually first-line treatment of glaucoma.  They work in two ways: improving the drainage or outflow of the aqueous humor, hence lowering the pressure or slowing down the production of that fluid in the first place, also lowering the pressure.  2017 brought the introduction of the first new IOP lowering medications since the 1990’s - Rhopressa and Vyzulta.  Multiple classes of these drugs are available as are shown below.

Laser treatments for glaucoma aim to open the drainage angle to allow fluid to flow out and result in a lower intraocular pressure (IOP).  A laser peripheral iridotomy will create a tiny hole in the iris to widen the drainage angle.  This is most commonly used with narrow or closed angle glaucoma.  Laser trabecuplasty does not create holes or other ducts, but instead stimulates with laser energy the existing drainage system, the trabecular meshwork, in an attempt to get it to function more normally.  There are two kinds of this procedure that your surgeon might use including argon laser trabeculoplasty (ALT) and selective laser trabeculoplasty (SLT).  The laser is effective in lowering eye pressure in 75-80% of eyes and the effect of the laser can last up to 1-5 years.

The goal of surgery is to create a new passage for fluid drainage, which in turn will lower the eye pressure. It is usually reserved for especially difficult cases where intraocular pressure cannot be controlled any other way.  They are also used for certain patients that are unable to consistently use their eye drops, such as the elderly that may have limitations with dexterity.  Several surgical options are available including trabeculectomy, tube shunt implants, and deep sclerectomy.  Trabeculectomy will create a filtering bleb between different areas of the eye to help with drainage.  A new drain is essentially created by removing a piece of the the old drain and creating a small hole in the white part of the eye (sclera) and covering it with a thin membrane (the conjunctiva of the eye).  The fluid will collect under this membrane and balloon out forming a “bleb” that will body will then gradually drain.  In a tube shunt procedure, a small flexible tube is inserted into the wall of the eye creating another way for fluid to drain.  This extra drainage pathway is to allow the eye pressure to drop, thereby achieving better control of your glaucoma and allowing the possibility of decreased reliance on glaucoma medications.  In a deep sclerectomy a filtering membrane is created for fluid to move out of the eye to underneath the conjunctiva to be drained by the body.