Glaucoma is often referred to as the silent thief of sight. Over time the optic nerve atrophy associated with glaucoma destroys your peripheral vision leading to tunnel vision and eventually complete blindness. Early detection is the key to preventing functional vision loss. Everyone is at risk for the development of glaucoma as they age, but there are a few other risk factors that raise the chance you might develop glaucoma. African-Americans, Hispanics as well as those of Mediterranean and East Asian descent have a greater risk. Ocular trauma, diabetes, ocular surgery, prolonged steroid use, uveitis and high blood pressure are also risk factors. Approximately 20,500 Nevadans have glaucoma.
Glaucoma comes in many forms and the treatments are just as varied. Here at the Visionary Eye Center we have the latest in glaucoma detection to help us monitor and treat our patients. Unfortunately, although we are able to detect and slow the disease, at this time there exists no cure.
Forms of Glaucoma
Primary open angle glaucoma (POAG)
Primary open angle glaucoma (POAG) is the most common type and comes in two forms, high and low tension. The eye’s anterior chamber has a constant supply of aqueous fluid produced that provides nutrition for the inner tissues of the eye. The trabecular meshwork drains the aqueous and is located in the angle formed by the iris and the cornea. The more familiar version of glaucoma is high tension POAG, where the pressure inside of the eye is elevated (>21mmHg) due to aqueous fluid production that exceeds the ability of the eye to drain adequately. This type of glaucoma is thought to be caused by blockage of the drain called the trabecular meshwork. Normal-tensive glaucoma is characterized by glaucomatous optic atrophy that occurs despite intraocular pressure being normal (<21mmHG). It is not currently known how this form of glaucoma occurs.
Primary narrow angle glaucoma (PNAG)
Primary narrow angle glaucoma (PNAG) is caused by the front surface of the iris coming into contact with the back surface of the cornea and trabecular meshwork, blocking drainage of aqueous fluid from the eye. This can cause a rapid increase in eye pressure leading to rapid vision loss, nausea, redness and pain. In some patients this can occur during prolonged periods of time in dimly lit conditions like a movie theater. A narrow angle closure attack is considered an emergency and needs to be seen immediately in order to prevent blindness.
Secondary glaucomas have many causes, from neovascularization of the angle due to diabetes, prolonged steroid use, tumors, pigment dispersion syndromes, trauma and uveitis.
Testing for Glaucoma
Tonometry is the measurement of intraocular pressure. It is one of the screening tests used in a wellness check and there are several devices that can provide this measurement, from the familiar air puff machine (non-contact tonometry) to the more advanced no puff iCare tonometer. The gold standard in monitoring pressure with glaucoma patients though is Goldmann Applanation Tonometry, which involves the instillation of a anesthetic with fluorescein dye, cobalt blue light and a small plastic tonometry tip. Tonometry is influenced by corneal thickness, as thinner corneas will cause low readings and thick corneas will cause high readings. Sometimes we will ask a patient to come in multiple times throughout the day to perform what is known as serial tonometry. This allows us to determine how much diurnal variation a patient has in the their pressures, as pressure is usually highest in the morning and lowest in the evening.
Pachymetry is the measurement of corneal thickness. This may be done either by ultrasound or optical coherence tomography. Knowing the corneal thickness is important in glaucoma treatment as it is known that thinner corneas are at greater risk of developing glaucoma and corneal thickness affects the accuracy of the measurement of intraocular pressure.
Automated perimetry measures your field of vision by flashing small lights in your periphery. This process has evolved over the years to improve the speed and accuracy of the test. Certain defect patterns such as arcs or nasal steps are typical of glaucoma. At the Visionary Eye Center we use the gold standard Humphrey Field Analyzer.
Optical coherence tomography
Optical coherence tomography (OCT) allows us to scan the thickness of the nerve fiber layer. Utilizing the advanced Cirrus OCT we are able to detect glaucomatous changes years before they cause visual changes with both nerve fiber layer analysis and ganglion cell analysis. With our Visante OCT we are able to visualize and precisely measure the chamber angle.
Ophthalmoscopy through a dilated pupil allows a stereoscopic evaluation of the optic nerve head and nerve fiber layer. Visual evidence of drance hemorrhages, notching in the cup and cup size ratio allows us to detect glaucoma during your eye exam.
Stereo digital imaging
Stereo digital imaging with our Canon non-mydriatic retinal camera allows us to take a 3D photograph of the optic nerve for future comparison.
Gonioscopy allows us to visualize the trabecular meshwork to detect pigment deposition and openness of the drainage angle using a contact lens with a mirror.
Treatment for Glaucoma
Medications are the first line treatment in the United States. Most patients are well controlled with minimal side effects. Preservative free versions that are sensitive to the ocular irritation that is the most common side effect are now available. There are also several good generic options for those patients where cost is an issue. Most of the medications are topical eye drops, but some are oral.
Prostaglandins are the most common eye drop prescribed first due to their safety, efficacy and ease of use (once a day). These drops work by increasing outflow. An interesting side effect from these drops is the enhancement of lash growth and darkening of the iris. The popular lash enhancement drug Latisse was developed based on this side effect. Examples of medications in this class include Xalatan, Lumigan and Travatan Z.
Beta-blockers are the original glaucoma medication. They function by decreasing aqueous production. Many of the medications in this class are generic and very cost effective. Some of the drugs in this class may cause problems for those with breathing troubles. Timolol and Betagan are commonly used drugs in this class.
Alpha-adrenergic agonists decrease aqueous production and increase outflow. These medications are typically not as effective as the beta-blockers and prostaglandins and are typically used as an additional treatment rather than a first line medication. Alphagan is the most common medication used from this class.
Miotic agents increase aqueous outflow by contracting the ciliary body. Pilocarpine is the most popular medication in this class. Common side effects are brow aches and difficulty seeing at night due to the decrease in pupil size.
Carbonic anhydrase inhibitors like Trusopt, Azopt and Diamox decrease the production of aqueous. These drugs are often used as an additive therapy as they are typically less effective than some of the other medications.
Oral hyperosmotics like isosorbide are used to rapidly decrease pressure in cases of acute angle closure attacks.
Laser surgeries like argon laser trabeculoplasty (ALT) and the newer selective laser trabeculoplasty (SLT) are great alternatives for patients that have trouble instilling eye drops or have difficulty remembering to take their medications. SLT is more commonly performed as it has been shown to be repeatable. These procedures aim to enhance the aqueous outflow by opening the chamber angle.
Trabeculectomy is the most commonly performed procedure for glaucoma. The surgeon will create an opening in the trabecular meshwork that allows aqueous to drain into the subconjunctival space creating a bleb, effectively increasing the volumetric space the aqueous has to use and decreases pressure.
Glaucoma valves or shunts are used typically when the traditional trabeculectomy has failed or if there are concerns that the trabeculectomy will not work. The mechanism of the surgery is very similar to the traditional trabeculectomy, with the addition of a valve or shunt to aid in the outflow of aqueous into the bleb.