The word “glaucoma” implies that the pressure inside the eye is high enough to cause damage to the optic nerve that runs from the retina of the eye to the brain.  This damage causes you to lose your ability to see.


There have been many things developed to measure the pressure inside the eye.  The first was to simply use your fingers to see if the eye feels abnormally hard.  Obviously this is very subjective and cannot identify small, but significant, increases in pressure.  Next was a device called the Schiotz tonometer.  This device has a piston that moves up and down inside a shaft that has a curved end to fit onto the cornea (front clear part of the eye).  How deep the piston will indent the eye is determined by three factors:  

1.  The pressure inside the eye

2.  The weight of the piston

3.  The stiffness of the tissue


One can increase the weight of the piston by adding a washer of known weight to it.  This is only necessary if the eye pressure is very high.



















The Schiotz tonometer was used for many years as the standard method for measuring eye pressure and is still a very economical method of doing so.


The applanation tonometer was the next device invented for measuring pressure.  The basic concept is that one presses a flat plate of known diameter against the cornea of the eye until the cornea touches exactly all of the flat plate.  One can determine the pressure necessary to cause the eye to flatten exactly this amount and convert that pressure into the pressure of the eye.  Obviously the higher the pressure in the eye, the more pressure it will take to flatten it to a known amount.  The applanation tonometer is usually attached to the eye microscope (known as a slit lamp) so the doctor/nurse can view down the center of the tonometer head to see when the exact flattening occurs.


For many years the applanation tonometer was the “gold standard” for measuring eye pressure.  It does require the skill of someone that can effectively use the eye microscope.  This encouraged the use of a device that did not require that skill and could thus be performed by someone not able to use the microscope.  In addition, both the Schiotz tonometer and the applanation tonometer require the use of an anesthetic drop to numb the eye to perform the test.  Many years ago, optometrists were not licensed to use these medications, so there was a stimulus to find another way to measure eye pressures.  This led to the development of the “puff tonometer”.  This involves blowing a puff of air of known quantity and intensity at the cornea.  The distortion caused by this puff of air changes the reflection of light from the cornea.  This distortion can be measured and converted to an estimate of the eye pressure.  This device is convenient for having a staff member measure the pressure, but it is generally hated by patients because of the startle that occurs even when you know the blast of air into your eye  is coming.  


In the 1990’s, a miniaturized and digitized version of the Schiotz tonometer was developed.  It is called the Tonopen.  One can simply “peck” at the cornea with this device and it will give you the pressure.  One advantage is that one can measure in the periphery of the cornea away from where Lasik is performed.  Measuring over the site of Lasik surgery with a Schiotz, applanation tonometer, or puff tonometer gives abnormally low readings.  Since so many people have had Lasik surgery, the Tonopen has become widely used.


You may experience any of these methods of measuring pressure when you visit your eye doctor.


There are several things that can give erroneous readings:

1.  Pressure from the squeezing of your eyelids while the pressure is being taken.

2.  Pressure from the fingers of the examiner.

3.  Change in the thickness of the cornea.

4.  Change in the elasticity of the sclera (white covering of the eye).

5.  Holding your breath while taking the pressure.


How Does An Increased Pressure Damage the Eye?


The eye is a part of the nervous system.  As such, it has a high demand for voltage, oxygen, and glucose.  All cells in the body are designed to run on fat as their primary fuel except for neurons.  They are designed to run on lactate (it used to be believed it was glucose)1.  The ability of the body to make lactate depends upon cholesterol sulfate.  “The ability of the heart and skeletal muscles to metabolize glucose depends critically on the bioavailability of cholesterol sulfate, which is supplied through sunlight exposure to the skin. When sulfate supplies are depleted, sugar piles up in the blood, and this can be very destructive to the blood proteins. The result of an overload of nutrients to a fragile vasculature is the formation of blood clots, for example, thrombosis, a life-threatening and vision-threatening condition.2


A normal liver can store about 1 1/2 hours of glucose for the nervous system and then it must be replenished if the nervous system is to run correctly.  As fuel (glucose) runs low, it is often vision symptoms that you notice first as your nervous system begins to malfunction.


The way that glucose/lactate and oxygen get to the eyes is by way of the vascular system.  If your circulation is inadequate, the nervous system begins to malfunction and eventually the neurons die.  On the left is a normal optic nerve.  On the right, dead nerve fibers have left a void in the center of the nerve called "cupping".
















The ability of the cardiovascular system and the respiratory system to bring blood and oxygen to the eyes is a careful balance of both systems.  Your heart must beat adequately to push the blood to the head and lungs.  You must have enough hemoglobin in your blood to carry oxygen to the eyes.  Your lungs must be able to move air in and out to provide oxygen to the blood so it can be distributed throughout the body.


A great problem in Western Medicine is that doctors forget that the body is a SYSTEM.  Heart doctors want the blood pressure as low as they can get it.  The reason is that the lower the blood pressure, the less work is placed on the heart.  They forget that it takes adequate pressure to push blood uphill to the brain and eyes.  Heart doctors and family practitioners/internists forget we have a brain and eyes.  Eye doctors forget we have a heart and often don’t check blood pressure to see if it is adequate to serve the needs of the eyes.  Both heart doctors and eye doctors tend to ignore the fact that the liver is the “fuel tank” for the brain and the eyes.  

Standard-of-care for glaucoma is to first use topical eye drops to lower the pressure in the eye in an effort to prevent nerve death leading to bllindness.  If the pressure isn't low enough with eye drops, oral medications are added.  If the combination of eye drops and medications aren't adequate to lower the pressure, surgery to create a new outflow channel for the fluid to excape the eye is created.


Sometimes a laser can be used to try to open the outflow channels, lowering eye pressure.  This technique can lower the pressure but a time, often a couple of years, but often has to be repeated.
















Low Pressure Glaucoma

There is a condition where the pressure is in the “normal” range but the retina and optic nerve malfunction as if the pressure were high.  This is called “low-pressure glaucoma”.  In standard-of-care medicine, the same procedures are used to lower the pressure more and more in an effort to prevent nerve damage/death.


Dr. Tennant believes this paradigm for low pressure glaucoma is incorrect but cannot be discussed on this "standard-of-care" website.  For a discussion on what the literature shows about this subject, you must leave this website and go to the the natural medicine website.











1 Wyss MT, Jolivet R, Buck A, Magistretti PJ, Weber B (May 2011). "In vivo evidence for lactate as a neuronal energy source". J. Neurosci. 31 (20): 7477–85. doi:10.1523/JNEUROSCI.0415-11.2011. PMID 21593331.


2  Seneff S, Lauritzen A, Davidson R, Lentz-Marino L. Is endothelial nitric oxide synthase a moonlighting protein whose day job is cholesterol sulfate synthesis? Implications for cholesterol transport, diabetes and cardiovascular disease. Entropy 2012, 14:2492-2530.


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