"Glaucoma," a condition that causes damage to the optic nerve
Glaucoma is a condition in which the intraocular pressure (water pressure inside the eye) increases, causing pressure on and eventual loss of the optic nerve.
While, together with cataracts, this is a condition the name of which is generally known as a disease affecting the eyes, there are probably only a few people with a correct understanding of the phenomenon.
Indeed, there are people who, upon hearing the word "glaucoma," go into a panic believing that they will lose their eyesight the following day.
The truth is that, in almost all cases of glaucoma, there are absolutely no subjective symptoms at the onset, the condition slowly developing over a period ten to twenty years, and as long as treatment is properly controlled, there is very little chance of loss of sight.
Let's start by improving our understanding of glaucoma.
Although the eyeball is shaped rather like a rubber ball, it contains various internal components and a uniform hardness (intraocular pressure) is maintained.
The most important factor in the maintenance of intraocular pressure is the flow of "aqueous humor," a fluid found in the eye.
As you can see in the illustration, this aqueous humor is produced by the ciliary body and flows along its main route from the Schlemm's canal located in the angulus iridocornealis, or corner angle (water outlet) to the venous duct, being completely transposed every 100 minutes or so.
Poor water flow from the corner angle results in accumulation of aqueous humor in the anterior chamber and a consequent increase in intraocular pressure. If this phenomenon persists and affects the optic nerve, the condition is referred to as "glaucoma."
While there are several types of glaucoma including those caused by congenital anomalies or aging and types occurring due to other diseases and conditions, glaucoma can be broadly divided into two categories, depending on whether the corner angle is wide and open (open-angle glaucoma) or narrow and blocked (closed-angle glaucoma). Anatomically speaking, there are people born with wide or narrow corner angles (some surveys have shown a high rate of incidence of people with narrow corner angles in western Japan), and, in addition to this, congenital narrowing of the corner angle may also occur for a wide variety of reasons including swelling of the crystalline body and the appearance of new veins.
The idea that glaucoma is a disease that quickly results in loss of vision came about due to acute glaucoma.
An attack of acute glaucoma causes obstruction of the flow of aqueous humor for some reason, resulting in a sudden increase in intraocular pressure, producing symptoms such as severe headaches or nausea. While such attacks may also produce symptoms including pain in the eyes, dim eyesight or iridopsia (the glare of lights will appears to be surrounded by rainbow colors), concerned about other symptoms, patients suffering from acute glaucoma may first tend to go to an internist or brain specialist, with the result that, by the time the condition has been accurately diagnosed, loss of sight may already have set in. It seems that the name "glaucoma" came into use due to observation in olden times that the pupils of sufferers of the condition became cloudy and greenish in appearance.
The vast majority of cases of acute glaucoma are caused by a blocked corner angle. In addition, during the process of production of new veins in people with diabetic retinopathy or other retinal vascular disorders, a time may come when an open corner angle gradually becomes closed or blocked. This is an ophthalmological condition requiring emergency treatment or surgical procedures to quickly lower the intraocular pressure.
In addition, surgical procedures that use lasers, for example, to open a minute hole in the iris, or surgery on the crystalline body (Surgery to remedy cataracts: This procedure widens the corner angle and is, therefore, sometimes selected for people with a narrow corner angle, even in cases where cataracts have not yet advanced to a problematic stage) are among the measures available to prevent the occurrence of this kind of acute glaucoma in people with congenitally narrow corner angles.
It should be born in mind that medication or various other drugs used during endoscopic examinations may bring on attacks of glaucoma in people with narrow corner angles, and this is why patients are often asked if they suffer from glaucoma during medical examinations.
It has been estimated by epidemiological studies that glaucoma occurs in 3.5% of people of the age of 40 or over in Japan, and open-angle glaucoma accounts for 90% of these cases.
In patients suffering from open-angle glaucoma, the corner angle that serves as the channel for water is open, but the drainage channel (Schlemm's canal) becomes blocked, preventing the outward flow of water, resulting in increased intraocular pressure. While this differs depending on the individual, normally, visual field sensitivity deteriorates extremely slowly, and this means that the condition may not be identified until has it has advanced to a considerable extent. For this reason, in many cases, the optic nerve has already been weakened by the time the person concerned becomes aware of the condition, with the result that many patients are already suffering the effects of considerably advanced visual field defects.
Moreover, it has been discovered that, in patients suffering with open-angle glaucoma, there is a very high incidence of "normal tension glaucoma," a condition in which the intraocular pressure (Normal value: 10 - 20 mmHg) is no higher than 12 mmHg. Although accompanied by visual field defects, like open-angle glaucoma, normal tension glaucoma has become the focus of attention as a disease caused not only by intraocular pressure, but related to a great many other factors such as cardiovascular abnormalities and environmental factors. Moreover, normal tension glaucoma is the most common type of glaucoma in Japan and, as a result, while in the past, factors including "intraocular pressure," "findings on the optic nerve head" and "visual field tests" formed important parts of examinations for open-angle glaucoma, "intraocular pressure" has become a less important consideration nowadays.
The approach that has been proven to be anatomically effective during actual treatment for glaucoma, including normal tension glaucoma, is reducing intraocular pressure. This slows the progress of the condition. Usually, the patient is started on a course of single-drug treatment with eye drops for glaucoma (Prostaglandin preparations are the first choice), but, depending on observations of the progress of intraocular pressure or visual field defects, 2 or 3 medications that provide other medicinal actions may be used, or the medication may be changed. If measures such as these prove ineffective in controlling the condition, treatment may include surgical procedures.
It should be noted that a special type of open-angle glaucoma known as "corticosteroid glaucoma" exists, and this type may occur concomitant with the use of steroidal eye drops or systemic administration of medications, for example. It is said that the ratio of responders (i.e. people likely to suffer side effects) among patients taking steroidal medications is 30% and users of such medications need to be watchful of their intraocular pressure.
Open-angle glaucoma is not such a terrible affliction as long as it is detected and brought under control in the early stages. That being said, open-angle glaucoma is characterized by a total absence of subjective symptoms in the early stages and this means that sufferers are unable to detect the condition themselves. People with this type of glaucoma do not become aware of problems with the visual field until the condition has already advanced to considerable degree, by which time progress of the condition cannot easily be arrested, even with treatment. Excessive myopia is also one of the risk factors for glaucoma, and it is advisable to be on the lookout for this telltale sign.
So, what can we do to spot glaucoma? First of all, once you pass the age of 40, it is advisable to take advantage of company health checks that include eye tests, regional health checks and thorough physical examinations. However, ophthalmologists are not usually present during these types of checkups, and the possibility of glaucoma is only spotted after observation of the optic nerve head depression during examination of photographs of the fundus of the eye after the checkup. For this reason, conditions that are not glaucoma are often spotted.
Diagnosis of glaucoma based on typical or advanced cases is simple, but the opinions of physicians on early stage cases are widely divided. In addition, since, once diagnosed, this is a condition that required continued, lifelong treatment and continued visits to an ophthalmologist, initial diagnosis requires great care. However, since the prevalence of normal tension glaucoma in Japanese people was established, use of diagnosis of intraocular pressure values has become less meaningful, and, even at my own outpatient practice, it is a fact that patients are sometimes erroneously diagnosed with glaucoma. I would like anyone who suspects that they are in the early stages of glaucoma, or has been diagnosed with the condition, to be aware that obtaining a second opinion by undergoing an examination by a different specialist is always an option.
Editorial supervision: Masato Wakakura, Director, Inouye Eye Hospital