Glaucoma, often called the silent thief of sight, is a disease of the optic nerve, which has little or no symptoms. The eye needs a healthy optic nerve in order for a person to see. It is the optic nerve that relays images and information to the brain. If the disease is not caught and treated in time, blindness may occur due to optic nerve damage. It is estimated that up to half the people affected with glaucoma are unaware of it. However, it is easily diagnosed with a routine ophthalmic exam. Glaucoma as of yet, has no cure and loss of vision cannot be reversed. Treatment of the disease can and will stop it from progressing. Since this is a chronic disease, monitoring must be maintained for life.
Glaucoma is divided into two broad categories based on the anatomy of the angle where the trabecular meshwork is found. They are open-angle and closed-angle.
– Open-angle Glaucoma
Over 90% of glaucoma is open angle, meaning the drainage system is open and not blocked by other structures. Within this category, the most common form is primary open-angle glaucoma. It is not uncommon for the eye pressure to be elevated which i thought to cause the damage to the optic nerve. However, one may have glaucoma and damage to the optic nerve despite having seemingly low eye pressures. There are several secondary glaucomas such as pseudoexfoliation or pigmentary glaucoma which are treated very similarly to primary glaucoma
– Closed-angle Glaucoma
This category of glaucoma is not as common but may be devastating if acute glaucoma ensues. Closed angle refers to the angle or drainage system of the eye which can get blocked by other structures in the eye, most commonly the iris. Some eyes have a particular anatomy such that the iris comes forward and blocks the drainage system. Since fluid is continually being produced and drained from the eye, if the drainage becomes blocked, the eye pressure can increase dramatically within a few hours and can cause havoc in the eye.
– Causes and Risk factors
The eye being a round and hollow structure needs pressure to maintain its shape and therefore its function. Fluid called aqueous humor, is produced in the eye then drained out by the drainage system of the eye called the trabecular meshwork (TM). The TM may get blocked thereby restricting drainage and cause elevation in the eye pressure. Abnormal increase in eye pressure can cause glaucoma and damage to the optic nerve.
Glaucoma is a disease that can strike anyone. There are some risk factors which may increase one’s chance of developing the disease. They are the following:
Anyone over the age of 60.
Family history of glaucoma.
African Americans, especially over the age of 40.
A complete eye exam will reveal more risk factors such as high eye pressure, optic nerve abnormalities and a cornea that is too thin.
In the early stages of the disease, there are no symptoms. As glaucoma progresses, a person may notice problems with side vision. By the time a person notices anything however, there will have been a great deal of damage to the optic nerve. The side vision or peripheral vision will slowly develop blind spots which get bigger as the disease progresses. Eventually the center vision will be involved where central vision loss will occur and eventual blindness will ensue.
The goal of glaucoma management is to catch persons before any vision has been lost. This is accomplished by routine and comprehensive eye exams.
– How is Glaucoma detected
Detection of glaucoma is accomplished simply through a complete eye exam, which includes the following:
Best correctable vision is ascertained.
The eye pressure or intraocular pressure is measured. Pachymetry or corneal thickness is measured. This is an important measurement which must be done for more accurate eye pressure evaluation.
The eye is dilated to assess the most important structure in glaucoma detection – the optic nerve. The nerve is carefully examined to determine if any abnormality or suspicion of abnormality is present. In addition, the retina and macula (the central part of the retina) is examined as well.
Visual field testing is done in order to measure the side vision of the eye. As described earlier, glaucoma initially affects the side vision so assessing this area of vision is crucial.
Computerized optic nerve imaging uses a different method to evaluate the optic nerve. This information is helpful because they are a separate and independent tool to further assess the optic nerve.
Medication can be used in the form of drops to help lower the eye pressure. The drops need to be administered once or multiple times a day depending on the medication in order to be effective. Compliance or remembering to take the medications is one of the drawbacks of this option because studies have shown that a large percentage of people tend to forget to take them. These medications may also have side-effects.
– Treatment of Open-Angle Glaucoma
Once a determination is made that the eye has glaucoma, treatment must be initiated. The goal of treatment for any kind of glaucoma is to lower the eye pressure. It is irrelevant how this is accomplished as long as it is done. It is important to note that glaucoma cannot be cured. As it is a lifelong disease, it must be monitored and managed on a regular basis.
The following are the treatment options for glaucoma:
Laser or Selective Laser Trabeculoplasty (SLT)
Laser or Selective Laser Trabeculoplasty (SLT) is a good option because it is a safe option with little or no side effects. The laser accomplishes what medications do and that is to lower the eye pressure. The laser works in most people however is some individuals, it has little or no effect.
This laser procedure is performed in the office setting. The eye is numbed and a lens is placed on the eye to direct the beam of laser to its proper place, which is the trabecular meshwork or the drainage system of the eye. It takes only a few minutes to perform the laser. During the treatment, you will feel no pain although some patients may occasionally feel a slight discomfort. You may see a green flash of light during the treatment process.
The mechanism of action of the laser is the following: The SLT employs a specific wavelength of energy in a very short duration of time – 3 nanoseconds to be exact. This burst of energy is absorbed only by melanin containing or pigmented cells found in the drainage system while the surrounding tissues are unaffected. The body clears these pigmented cells and the overall effect is to open the drain. More fluid is able to drain out of the eye so the overall eye pressure goes down.
The full effect of SLT sometimes takes a few weeks to a month to kick in and a follow up visit will determine how effective the SLT was.
One of the main benefits of SLT is that it is not associated with systemic side effects, unlike drops which are absorbed by the eye as well as the body. Compliance with medications or having to remember to take the drops is not an issue with the laser since it works on its own 24 hours a day. This procedure is covered by Medicare and most health insurances.
The laser will generally last for several years and may be repeated in the future if the effect wears off.
SLT works in most kinds of glaucoma.
IStent - Microinvasive glaucoma surgery or MIGS
iStent is a new device approved by the FDA available for glaucoma patients undergoing cataract surgery. The IStent bypasses the area of resistance that causes the eye pressure to increase thereby lowering the pressure after the procedure.
The primary cause of elevated intraocular pressure (IOP) in patients with open-angle glaucoma is abnormality of the trabecular meshwork. With up to 75% of resistance to outflow located in the juxtacanalicular tissue, the iStent safely improves outflow by creating a patent bypass between the anterior chamber and Schlemm’s canal. iStent improves outflow with a single bypass.
The Istent implantation is safe and very effective in lowering the pressure. It’s the smallest medical device to be implanted in the human body measuring only 1 mm in length. The dimensions of iStent are customized to optimize fluid outflow while fitting naturally within Schlemm’s canal. Its three retention arches ensure secure placement.
Each iStent system is comprised of a surgical-grade nonferromagnetic titanium micro-bypass stent so it is safe if an MRI is performed in the future.
Glaucoma surgery is necessary in those patients where medications and laser have not been effective enough. It is reserved for those with more advanced or difficult to control glaucoma.
A glaucoma drainage device (GDD) is implanted, which channels aqueous fluid from the anterior chamber to a reservoir.
The procedure is done in an operating room with mild sedation and local anesthesia, so that the procedure will have no to little pain.
After an incision is made in the conjunctiva (outermost surface of the eye) the device is placed in the proper place. A tiny opening into the eye is made and a tube, which is connected to the drainage device, is inserted into the opening so that the aqueous fluid may be drained out of the eye. When the fluid is drained out of the eye, the eye pressure will decrease and bring the disease under control.