Stages of Glaucoma Progression
January 26, 2005
Norma Devine, Editor
On Wednesday, January 26, 2005, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed “Stages of Glaucoma Progression.”
Moderator: Many believe that glaucoma damages the peripheral vision first, but glaucoma doctors and patients seem to have a different understanding of what peripheral means. Where does glaucoma first occur in the visual field and is that considered to be peripheral?
Dr. Rick Wilson: The visual field test that you all take extends out to 30 degrees from the center. Therefore, peripheral visual field loss on that test is only part way out to the 90 degrees that we see temporally. The earliest nerve damage secondary to early moderate nerve damage is usually above the center of vision, 15 to 20 degrees from the center, or in the nasal field 20 to 30 degrees from center. Remember that 35 to 45% of the optic nerve is damaged before consistent changes appear in the visual field.
P: Instead of saying that glaucoma affects peripheral vision first, shouldn’t that be phrased in another way?
Dr. Rick Wilson: It is more correct to say that glaucoma affects a doughnut of vision around the center, sparing the center and the periphery till later in the disease.
P: What is a nasal step?
Dr. Rick Wilson: Nerve fibers from the optic nerve spread out across the retina. They stop on the temporal side of the optic nerve at the horizontal midline of the retina. Therefore, damage above or below what is called the horizontal raphe produces asymmetric loss at the nasal mid-horizontal line. That often looks like a step. [A “raphe” (pronounced “ruh-FAY) is a demarcation line, similar to a seam, dividing two halves of an organ or structure. In the eye, it refers to a horizontal line separating the upper from the lower temporal retinal nerve fiber layer patterns.]
P: What is a scotoma?
Dr. Rick Wilson: Damage to optic nerve fibers occurs diffusely, which is hard to notice as the whole field becomes less sensitive, and/or in a patchy distribution in the retina. Patches of dead or dying retina from pressure on the nerve that supplies them with growth factors give localized areas of decreased sensitivity to light in the visual field. That hole in the field is called a scotoma.
P: An ophthalmologist told me glaucomatous loss of vision seems generally to occur in pronounced steps, rather than as a gradual dimming of vision.
Dr. Rick Wilson: Early on in the disease, when there are 1.0 to 1.5 million fibers in the optic nerve, loss is usually gradual. When the loss is extensive and the visual field is small, the loss often is more stepwise than a gradual downward slope.
P: My year-old daughter seems to do quite well in low light. Why is that?
Dr. Rick Wilson: Patients with congenital glaucoma have young, soft eyes that stretch with the high pressure. The stretching and the pressure of fluid pushing into the cornea causes light sensitivity. Your daughter probably does better in low light because her corneas are sensitive. Most patients with serious glaucoma do worse in low light because there is less contrast in what they are looking at.
P: My husband has been complaining that any breeze or wind in his eyes causes a considerable amount of discomfort. Is that normal for late-stage glaucoma? The light sensitivity is extreme to the point that it is more comfortable for him to go around with his eyes closed, rather than open.
Dr. Rick Wilson: Your husband’s symptoms may be related to allergy or toxicity of the medication, possibly combined with dry eyes. Both make the eyes much more sensitive to wind and light.
P: Is there a certain pattern the vision loss follows, such as blurred vision first, then colors not as bright, for all glaucoma patients?
Dr. Rick Wilson: There does not seem to be a definite pattern that fits all patients. Some patients lose blue-yellow sensitivity early in the disease, while others have excellent color vision with limited visual fields. Most lose some contrast sensitivity as the disease progresses.
P: Can a doctor determine if loss of color vision and contrast sensitivity are caused by cataract or by glaucoma?
Dr. Rick Wilson: Modern visual field testing machines have a statistical package that helps select out localized defects from the global decrease in sensitivity due to cataracts. Some tests, frequency-doubled perimetry for example, are hindered by cataracts. The extent of visual field loss usually defines the extent of glaucoma damage, as well as the condition of the optic nerve.
Moderator: What are the most important factors in determining if and how glaucoma damage will progress?
Dr. Rick Wilson: The main factors are intraocular pressure, genetic susceptibility to pressure, adequate blood pressure and circulation, and thickness of the cornea. Other factors, such as race, are important. Nearsightedness and diabetes play a lesser role.
P: In my family’s case, damage shows up first in the outer area that only the 30-2 visual field test catches. Months later the damage spreads to adjacent (more central) areas in the 24-2 test. I know the 24-2 is a bit faster, but not much. It seems to me that the 30-2 is worth doing more often, or is my family relatively atypical?
Dr. Rick Wilson: The 24-2 goes out to 30 degrees nasally. It is only the temporal area, where little is going on, that the visual field is constricted to 24 degrees.
P: I had an eye exam by an ophthalmologist in July of 2002 (slit lamp, wall chart, etc.) Everything seemed fine, and my myopia had lessened significantly, so I was given a new prescription for glasses. Eight months later, I had a large scotoma in one eye and an optic pit corresponding to the field loss. My intraocular pressures (IOPs) were normal. Does that sound like progression of normal-tension glaucoma? Also, can you talk about progression in normal-tension glaucoma, generally?
Dr. Rick Wilson: You would need to have IOPs checked throughout the day to know if they ever went above 22 mm Hg. The only differentiating factors about patients with normal-tension glaucoma and how they progress are the consistently normal IOP, a greater frequency of tiny hemorrhages, called Drance hemorrhages, on the edge of the optic nerve, and a tendency to have dense visual field defects close to the center of vision. The nerves exhibit less tissue for the same amount of visual field loss.
Moderator: Does the attitude of the patient affect progression of glaucomatous damage?
Dr. Rick Wilson: Absolutely. A compulsive person who always instills the eye drops on time has a far better chance than a recalcitrant or forgetful patient. I also think that a positive attitude and sense of humor help a great deal.
P: How many visual field tests are needed to form a baseline that is used to help determine if the patient is losing visual field?
Dr. Rick Wilson: Two if they are similar; best two of three if they are not similar.