What is Glaucoma?
By definition, glaucoma is a disease that damages the optic nerve of the eyes. Your eye has a steady pressure (different to your blood pressure) called the Intraocular Pressure or IOP. If it increases to dangerous levels it damages the optic nerve. This can result in decreased peripheral vision and, eventually, blindness. People may have high IOP without accompanying nerve damage and vision loss, and this is called Ocular Hypertension.
How the Eye Works
This is essentially the explanation I go over with all my patients in the office utilizing the eye model for demonstration. To understand best, I compare the eye to a camera.
As light enters the eye it first passes through the cornea, the clear 'window' to the eye. Because the cornea is curved, the light rays bend (refract). Light then passes through the pupil which is the opening formed by the iris. The iris -- the colored portion of the eye, controls the amount of light that enters the eye with muscles that cause the pupil to contract if there is too much light, or to dilate if there is too little light. Light then travels through the lens of the eye. When light hits the curved surface the lens it is refracted, or bent even more, so that it focuses properly on the retina. The retina is like the ‘film’ of the camera – it takes the picture. From the retina light is turned into electrical energy, which passes by way of the optic nerve to the occipital lobe if the brain where it is converted into an image that we perceive.
What Controls the Eye Pressure?
In a camera, between the lens and film there is an air space, in our eye this pace is filled with a clear jelly and fluid. The fluid is made in the back of the eye and is called aqueous humor. The aqueous provides the eye with nutrients and oxygen. If this fluid was being continually produced and did not drain anywhere, pressure in the eye would build up very high and would destroy the eye like filling up a water balloon and not stopping. However there is a drain for the fluid, and that is actually in the front of the eye. The fluid that is produced in the back percolates throughout the back of the eye, goes around the lens through the pupil and then exits the eye in what we call the anterior chamber angle. There is a sieve-like structure through which the fluid drains.
In most people the drain works fine with a normal resistance and produces a normal pressure in the eye. This pressure ranges between 10 to 20mm of mercury with an average of 16mm. If the resistance to flow is increased the pressure builds and nerve fibers in the back of the eye get damaged and ‘die’. As we lose these fibers we start losing side vision. In some people this can happen even if the pressure is in the normal range. This is called Normal tension or Low tension glaucoma. It is important to diagnose and treat this condition early.
In all types of glaucoma it is shown that lowering intraocular pressure does successfully preserve and save nerve tissue.
It is important to recognize that we cannot bring vision back in patients with glaucoma, but our goal is the stop the progression of visual loss. It is therefore critically important for us to diagnose glaucoma early and treat it early.
Treatment
The first step in treatment is evaluation. The four areas of importance are intra-ocular pressure, state of the optic nerve head, visual field testing, and examination of the chamber angles.
Someone ultimately becomes a glaucoma suspect when they have risk factors linked to developing glaucoma without necessarily presenting any current defined glaucoma damage, such as damage of the optic nerve or visual field defects. These risk factors include:
In addition, we have also recognized that the corneal thickness plays a role in our measurement of intraocular pressure. If during a routine eye examination we find any of these risk factors, we will discuss these with you and develop appropriate plans for base line testing and regular follow-up visits. In some cases we may even treat the IOP in patients that do not yet have damage if the risk factors appear to be great enough. For patients that are suspects a s well as known glaucoma patients regular follow up evaluations and repeat testing in these four areas of concern (visual fields, angles, optic nerve head, and IOP) are vitally important.
Our goal is to provide you with the best eye care possible.
If you have any questions or concerns regarding your chances of having glaucoma or being a glaucoma suspect, the best way to alleviate your fears is the schedule a comprehensive eye exam so that your doctor can evaluate these factors, and help your pressure your precious gift of sight.
