There are certain ocular diseases that we all know can cause blindness, and we know that we should be checked for those at every eye examination.  But during my tenure as an optometrist, I have discovered that while most people have heard of conditions like glaucoma, cataracts, and macular degeneration, we haven't done a very good job of telling people what those ocular conditions actually are. Glaucoma is a disease of the eye where the optic nerve is destroyed, causing permanent visual loss.  For more details, please read this post.  What most people don't realize is that diagnosing glaucoma is a very complicated process.  Your doctor can't just look at your eyes and say "You have it!" (unless it is very advanced that is).  Here is a breakdown of all the information your doctor is collecting to screen your eyes for glaucoma at every eye examination:

1) Checking the pressure inside the eye

Goldmann's Tonometry is a more accurate pressure reading that is often used to verify NCT (or air puff) data

The dreaded air puff test has an important goal-- it tells your doctor the pressure inside of your eye.  A range of pressure between 10 and 21 mmHg is considered normal, but some people are going to have higher pressure and it still be normal for them.  The air puff (or non-contact tonometer) is a preliminary screening tool.  If your pressure is high, it does not mean you have glaucoma.  If your pressure is normal, it does not mean that you don't have glaucoma.  Your eye pressure is going to be different depending on the time of day, the medications you take, whether you are sitting or lying down... Lots of things can vary.  But over the course of several years of pressure data, your doctor is compiling a trend for your "normal" pressure, which can help them find suspicious changes with time.  For example let's say you have a pressure of 10 for several years, and the next year we check your pressure and it is 18 mmHg.  That is still a normal pressure reading according to our "average range", but it is not normal for you!

2) Inspecting the Anatomy of the Eye
I don't want to make this too complicated, but when the doctor looks at the surface of your eye in the microscope, they are checking for numerous medical conditions, including suspicious structural changes that could cause acute spikes in your eye pressure.  If the anatomy of your eye where the cornea meets the iris (colored part of the eye) is very narrow, you are in a higher risk category for having this acute spike.  This is something your doctor measures at every examination, and will record in your chart whether this structural meeting place is "wide open" or grade the amount of narrowing on a scale of 1 to 4.  If you are in the 1-2 range on this grading scale (very narrow), your doctor will be discussing the signs and symptoms of an acute angle closure attack.  If you have acute onset redness, pain, blurry vision, and halos around lights, you need to be seen immediately!

3) Inspecting the Anatomy of the Optic Nerve

Via

The optic nerve is a like a chord that hooks the back of the eye to the brain.  In the retinal photographs that many doctors take, it looks like a yellow circle.  Inside of this chord, blood vessels run through delivering oxygen and nutrients to the eye.  That means that there is a hole inside of the nerve to let the vessels pass through.  In doctor-speak, this hole is called "the cup".  To make things as simple as possible, the bigger your hole, the more at risk you are for glaucoma, because in glaucoma the nerve tissue is dying, which would cause the hole to get bigger and bigger, or more hollowed out if you will.  Here's the catch -- not everyone with a large hole or "cup" has glaucoma.  Some people just genetically will have a large hole.  And not everyone with a small cup does not have glaucoma.  I have seen several patients with a small cup that had diffuse visual field loss from glaucoma.  There are some trends that help your doctor determine if your nerve "cup" size is normal:

• Is the size of the cup the same in both eyes?  If you have one large hole and one small hole, there is a greater chance that the eye with the large hole has a disease process.  Usually in nature we are symmetric in anatomy, so we would expect the right and the left eye optic nerve to look the same if it was healthy and normal.
• Is the size of the cup the same as last year?  As 10 years ago?  This is where photodocumentation is pivotal.  In a normal eye, the size of the hole in the nerve will not be changing from year to year.  If you have photos of your eye over a lifetime, it can be very beneficial to have your doctor compare to check for gradual changes.  If you started out with a smaller hole and now have a larger hole a few years later, that is very suspicious for glaucoma.
• Is there bleeding around the nerve?  A hemorrhage near the nerve is often a sign of glaucoma (called a Drance hemorrhage).
• The bigger the nerve, the bigger the cup.  This is a just a rule of thumb -- not everyone has the same size optic nerve.  If you have a larger optic nerve, your doctor expects you to have a larger hole inside the nerve.  What is a normal size hole in one person with a large nerve, could be a major glaucomatous process in another person with a smaller nerve size.  It is all relative!

This picture is from the right and left eye of the same patient.  Look at the asymmetry of the cup or hole inside the optic nerve!  The large hole inside the nerve on the right side of the photos is a major giveaway that this person probably has advanced glaucoma.

Glaucoma is a spectrum of ocular diseases that cause optic nerve destruction

There are so many different types of glaucoma, and all of them work in different ways.  One thing unites them all: the optic nerve that delivers the message from the eye to the brain is destroyed.  The destruction is most commonly slow and painless, but in some types of glaucoma can be very quick with acute headaches and halos around lights.  Damage to the optic nerve causes PERMANENT vision loss, and that is why glaucoma is such a devastating ocular disease.

To simplify this discussion, let's talk about the most common form of glaucoma: primary open angle glaucoma.

Glaucoma typically is caused by high pressure building up inside the eye.  There is a fluid called the aqueous humor that is made to deliver nutrients to the internal components of the eye.  If too much fluid gets made, or if too much is retained inside the eye instead of draining out into surrounding tissue, then the fluid builds up in the eye.  This creates increasing pressure pushing against the back of the eye and the delicate optic nerve.

Eye Pressure or Intraocular Pressure

Goldmann Tonometry, the "gold standard" pressure reading Photo via http://www.sco.edu/

Every time you visit your eye doctor, a pressure reading is taken.  Most commonly an "air puff" is used, but there are also sophisticated hand-held and microscope attached instruments called tonometers that can be used.  Pressure is measured in mm of mercury (mmHg).  Average pressure is 10-21 mmHg.  Typically numbers over 21 are considered elevated, and thus suspect for glaucoma, but there are varying factors that may affect these eye pressure readings.  Your doctor will investigate further if your pressure is reading high.


What Glaucoma Looks Like

Most offices use retinal photographs to show patients what an eye disease looks like, but glaucoma is a disease that is not easy to "see."  What your doctor looks for to detect glaucoma is atypical appearance of the optic nerve.

Photo via http://www.glaucoma-eye-info.com/

Everyone has a hole in their optic nerve where blood vessels pass through.  The average person has a hole that is smaller than half the diameter of the nerve (is that complicated enough??).  The photo above shows a normal, small hole. The larger the hole, the generally more suspicious it is for glaucoma.  Here's the thing, everyone has a different size optic nerve and a different size hole that can be entirely normal.  In the average eye, the size of that hole is constant through life.  In glaucoma, the size of the hole in the nerve will get LARGER with time, because the nerve tissue is getting destroyed.  This is why taking routine retinal photography is such a great option, and why everyone should be routinely examined by their eye care professional even if they don't have vision trouble or had no eye diseases several years prior.  Glaucoma is PROGRESSIVE, which means you might not have it today, but you may have it in a few years.  The only true way to detect it is by monitoring for changes.

2003

2011: Note hole or cup is getting BIGGER near the bottom edge. If you look close, you can see a hemorrhage near the area of inferior damage (a tell-tale Drance heme)

2012:  Even thinner at the inferior edge of the nerve!!