Don’t Forget The Angles
According to the authors of the “Atlas of Glaucoma” by Dr. Paul Henkind and Dr. Richard Starita, “the simplest definition of glaucoma is that condition of the eye where the intraocular pressure is elevated beyond the limit that will permit normal function of the optic nerve.”
This definition implies the presence of an abnormal intraocular pressure, generally above 21 mm Hg, which is somehow due to an abnormality in aqueous drainage from the eye or an impediment to aqueous outflow from the posterior to the anterior chamber of the eye. This definition also suggests that the intraocular pressure elevation affects the nerve fibers of the ganglion cells, the final neural pathway from the eye to the brain. The fact that this definition is simplistic is easily demonstrated by the patient with the so-called “normal” intraocular pressure, generally below 21 mm Hg who has typical glaucomatous cupping of the optic nerve head and characteristic visual field defects. Then there is the patient with marked elevation in ocular pressure, usually from an inflammatory condition, who sustains no optic nerve alterations even after a protracted period of time.
Thus, glaucoma defies a simple explanation. As ECP’s, we must remember that a diagnosis of glaucoma can be a scary ordeal for a patient who is now encountering new fears, anxiety, medical uncertainties, new financial concerns with doctor bills, surgical bills, and the increasing costs of medications. It is our responsibility to educate and to calm our patients’ fears. This may also involve other family members especially when a patient may be elderly or unable to understand the severity of the problem. If these patients are in an assisted living facility or in a nursing home, direct communication with the medical staff and nursing staff concerning all aspects of the patient/residents’ eye care will be necessary.
The human eye has a very important anatomical structure called the angle of the eye that plays a significant role in the health of our visual system. The angles of each eye need to be viewed under a bio-microscope and a gonioscopic lens in order to determine if the angle is open, closed, narrow, or if the angle can potentially close in the future. Gonioscopy allows the anatomical structures of the angle to be seen directly including Schwalbe’s line, the trabecular meshwork, the scleral spur, the ciliary body band, and the iris processes. I have heard of cases in offices where patients have been dilated before their angles have been evaluated. The angles should always be evaluated first before any dilating drops are used for fear that the iris can close off the angle and create an attack of closed angle glaucoma which has the potential to become an immediate emergency.
Patients who are at risk for narrow angle glaucoma include people with sudden eye pain, patients who develop headaches and red eyes, elderly patients, the Asian population, patients with a family history of glaucoma, and women. Angle closure glaucoma occurs three times more frequently in women. Among African-Americans, men and women appear to be affected equally. Due to the fact that there are many different types of glaucoma, many factors must be evaluated before a diagnosis is made and/or treatment is considered. Medical problems including diabetes and hypertension can affect the intraocular pressure. Corneal thickness, angle evaluation, visual field testing, gonioscopy, cataract evaluation, refractive conditions, intraocular pressures with diurnal variations, fundus photos, and dilation when appropriate must all be done for every patient, especially for the at-risk population.
When I have discussions with my patients concerning the aqueous fluid that flows in the posterior and anterior chambers, some think that this fluid is actually the tear film which forms above the cornea. They are surprised to learn that the aqueous fluid created by the ciliary body is within the eye. Most patients have never heard of the angles of the eye. The pressure created by the aqueous fluid can potentially create a higher-than-acceptable pressure causing damage to the optic nerve resulting in glaucoma. According to Adler’s Physiology of the Eye, “the aqueous fills the anterior and posterior chambers of the eye. The aqueous is a slowly flowing stream into which surrounding tissues can discharge waste products of metabolism. By means of a steady aqueous formation and drainage, the intraocular pressure is maintained and the globe is preserved in an optical form with the position of the refractive surfaces relative to one another.” Aqueous humor forms at a rate of 2 microliters per minute, and this volume changes completely every 100 minutes. Aqueous humor flows into the posterior chamber of the eye then flows through the pupil into the anterior chamber. Aqueous humor then escapes from the anterior chamber and returns to the bloodstream by two routes, the uveoscleral outflow route and by leaking through the trabecular meshwork into Schlemm’s canal.
If the angles are narrow, a patient can have narrow angle glaucoma (NAG) or possibly be at risk for this type of glaucoma. Sometimes we classify these patients as “glaucoma suspects” until enough risk factors or problems develop to identify them as having glaucoma. The suspicious patients need to be seen more frequently and need to be advised with proper education, counseling, and viewing appropriate medical websites. These patients need to be aware of the costs, risks, and benefits as to their current status and what may lie ahead in the future. Medications and surgical options can be discussed with the knowledge that research and new innovations are constantly changing in the area of treatment options.
Before the determination of NAG can be reached, many variables must be evaluated. The optic nerve and retina must be evaluated and the cup to disc ratio must be analyzed. Before any patient is dilated, the angles must be graded from 1-4; 1 being narrow and 4 being wide open. If the angle is closed or very narrow, extreme caution must be exercised and I never dilate a patient with these types of narrow angles. Dilating these patients can possibly create an attack of NAG as the iris widens and closes down the flow of aqueous fluid. If there is a complete angle closure, the continued formation of aqueous humor can cause the intraocular pressure to rise.
A partial angle closure may produce a moderate ocular high pressure (ocular hypertension) and can result in a slow vision loss. Patients at risk for angle closure glaucoma include those people who have a family history of this type of glaucoma, people who are farsighted, people whose cataracts are “crowding” the angle or those people who have a large lens, patients who experience pupillary block which can develop from using antihistamine eye drops, the development of posterior synechiae from ocular inflammation or an iritis or uveitis, choroidal detachments, ciliary body melanomas, or malignant glaucoma where the aqueous is misdirected. Labels on over-the-counter cold and allergy medications sometimes have warning labels that say “do not use if you have glaucoma”. Antihistamines usually have no effect on open angle glaucoma. But people with narrow or closed angles should be advised that these medications can cause pupil dilation and can cause an attack of angle closure glaucoma.
The surgical treatment of angle closure glaucoma is to increase the passage of aqueous from the posterior chamber to the anterior chamber. A laser peripheral iridectomy (PI) or a peripheral iridotomy will allow the movement of aqueous through a laser-induced, new hole and will help to reduce the intraocular pressure. Only one eye is lasered at a time. If a laser PI is not possible to do, then another option is a surgical iridectomy. Other more serious options are a trabeculectomy when the IOP remains high despite previous treatments including a PI and maximum medical treatments. These options are usually considered when there is significant optic nerve cupping. There is a new device called an I-stent that is being used to treat glaucoma patients, but it is being used for open angle glaucoma patients, not narrow or closed angle glaucoma patients.
Depending upon state laws, optometrists can treat and manage glaucoma patients. When treatment is needed for NAG and lasers are used for a PI, opticians and optometrists must refer these patients to an ophthalmologist who is a glaucoma expert. There are some states where optometrists are seeking the right and privilege to use lasers. These standards of care may change in the future depending upon the laws of each state. Every office should have a plan as to how to manage referrals of any kind especially for complicated patient problems or emergencies. ECPs are fortunate that there are specialists at every level and in many different locations to provide the highest quality of eye care possible with the hope that some difficult problems will have a positive outcome.
Jason Smith, OD, MS