Glaucoma: the Sight Stalker

Glaucoma is a very common, insidious, chronically progressive disease of the optic nerve, which if not treated and stabilized, results in irreversible loss of vision. In most cases, it causes no notable symptoms until very late in the disease process, when central vision has been permanently reduced. Glaucoma is treatable, and vision salvageable, if the diagnosis is recognized early, prior to vision loss.

There are many types of glaucoma; they all have in common the underlying pathology of the disease, which is described as progressive “cupping”, or excavation, of the optic nerve head. This progressive optic nerve damage occurs due to possibly a number of adverse effects, most notably intraocular pressure.

Increased intraocular pressure is the most consistently proven, dose-related risk factor known to cause glaucoma in most cases, and treatment in all cases is aimed at lowering and controlling eye pressure. Other risk factors may include peripheral vascular disease such as high or low blood pressure, diabetes, sleep apnea, Raynaud’s phenomenon (inappropriately cold hands and feet), ocular migraine syndromes, and atherosclerosis, especially with regard to the carotid arteries. Increased age, a family history of glaucoma, and near-sightedness, or myopia, also increase a person’s chance of having the disease.

The optic nerve head is the “coming together” of all of the retinal nerve fibers lining the posterior segment of the eye. The health of these nerve fibers is essential for vision. After these long nerve fibers coalesce on the head of the nerve, they exit the back of the eye and travel as the optic nerve bundle to the brain, where they then divide and travel to different regions of the brain to help produce vision images. (figure 1)



If the fluid pressure inside the eye is inappropriately high for a particular eye, it exerts mechanical “crushing”, excavating damage on the head of the optic nerve, which results in progressive death of the long retinal nerve fibers. This leads to progressive, irreversible loss of vision if not treated. (figure 2)



Progressive loss of vision due to glaucoma, as well as some other neurologic diseases, such as pituitary tumor, and some other brain tumors, can be discovered and followed by testing “visual fields” over time. This is the only currently available method of assessing a patient’s functional peripheral (side) and central vision. Although the testing is fairly tedious for the patient, visual fields can be critically useful in predicting risk of central vision loss before it occurs. (figures 3, 4)



Also, we now have commercially available computerized instruments, which are capable of measuring the nerve fiber layer thickness surrounding the optic nerve head; these nerve fibers are usually the first to be damaged by glaucoma, a long time prior to initial visual field and vision damage.

Both visual field testing, and computerized optic nerve analysis are invaluable for following patients with glaucoma, and can predict the risk of functional vision loss before it occurs.


The pressure debate: how high is too high?
Even though we know that intraocular pressure is the most consistently proven risk factor for developing glaucoma, the relationship between increased eye pressure and glaucomatous damage is not a direct one. Not all “high” eye pressures should be treated, and some “normal” eye pressures should be lowered aggressively!

Most humans have an intraocular pressure of 16 to 22 mm Hg, and it varies considerably during a 24-hour period, with the highest pressures being typically in the very early morning hours.

We have a wealth of data in the literature, which has shown, that for people who have an eye pressure of 30 mm Hg, and who present with healthy optic nerves, the statistical chance of developing glaucoma is only 10% to 30% (the minority of these people will develop glaucoma; a pressure of 30 may be normal for these people).

On the other hand, we now know that 50% of people who lose vision from glaucoma, are never documented as having “high” eye pressure! Nonetheless, the literature repeatedly teaches us that lowering even these patients’ eye pressures tends to be protective and prevent glaucomatous vision loss.

So, it is critically important that the diagnosis of glaucoma be based on the appearance and health of the optic nerve head, and not on the specific intraocular pressure! This emphasizes the importance of regular, repetitive dilated eye exams, even for healthy people with no vision symptoms and no known medical problems!

Once the decision is made to lower a patient’s eye pressure, the most protective goal is a 30% decrease, and/or achieving an eye pressure of less than 18 mm Hg, in some cases near 10 mm Hg. (For cases in which damage is more advanced, a lower pressure is better.)

We have several categories of treatment options, including eye drops, laser treatment, and surgery. Dramatic technological advancements have increased our choices within each of these option categories. In general, by far the highest treatment success rates are seen with surgery, which is appropriate for those patient’s who have threatened central vision, and nonsurgical treatment options have failed or are inappropriate due to risk of imminent vision loss.

Timely, aggressive treatment, which is aimed at lowering and stabilizing eye pressure, is the mainstay of successful preservation of vision for patients with glaucoma. Early diagnosis is essential, and lifelong compulsive follow up is mandatory, in order to detect optic nerve and visual field change prior to the risk of further vision change.