Concentrate on the essentials when treating glaucoma patients

Glaucoma patients are most concerned with the quality of their vision, not IOP, visual fields or optic discs.

Issue: April 1, 2006

ByGeorge L. Spaeth, MD

George L. Spaeth

For patients, the only real significance of glaucoma is that it can disable them. Of course we physicians are concerned about keeping our patients from becoming disabled and preventing those who already have a disability from becoming more incapacitated. But we are so entangled with the important details of the mechanics of care — measuring IOP, obtaining a meaningful history, filling out complex forms — that we may ignore the forest through the trees, forget that the IOP, the field and the details of the forms are only the indicators we use to try to keep patients healthy; they do not constitute health themselves.

In ophthalmology, disability is related primarily to reduced vision, although it can be the result of pain, emotional problems or the wide variety of side effects caused by the treatments employed. Many markers of the severity of illness in patients with ocular conditions are those that are easy to measure — IOP, visual field loss or even damage to the optic nerve. In contrast, disabilities, as shown by a worse quality of life or an inability to perform the activities of daily living, seem to be hard to measure, define and quantitate, so they are often ignored. But unless educated differently by us, patients do not give a whit about their IOP or their visual field or their optic disc. They care about symptoms and disability, and they care about worsening symptoms and worsening disability.

Because we concentrate on indirect measures of disability and because we rarely attempt seriously to develop quantitative estimates of rate of change, we may allow real disability to develop unnecessarily and may make patients ill with medications unnecessarily, as we try to prevent projected disabilities that do not exist and will not actually materialize. Phrased differently, we tend to concern ourselves mainly with surrogate measures, such as IOP or visual field loss, when the primary outcome measures should be quality of life and activities of daily living.

Indications of glaucomatous process

Glaucoma is a process that presents identifiable signs including characteristic optic nerve damage, peripheral anterior synechiae, the presence of a gene associated with the development of glaucoma and IOP so high that it virtually never occurs in the absence of the glaucomatous process. In this regard, IOP over 40 mm Hg or IOP asymmetry of greater than 50% between the right and left eyes are findings highly suggestive of the presence of the glaucomatous process. Characteristic changes in the discs sufficiently typical that they are diagnostic of the process include an acquired pit of the glaucomatous nerve (Figure 1), absence of the rim in average or small-sized discs (Figure 2) and a rim narrower than 0.1 rim/disc ratios in a small disc (Figure 3). A Disc Damage Likelihood Scale (DDLS) score of 6 or greater is a characteristic sign of disc damage (Figure 4).

Characteristic changes in the disc are sufficiently typical that they are diagnostic of the glaucomatous process include acquired pit of the optic nerve.

Characteristic changes in the disc are sufficiently typical that they are diagnostic of the glaucomatous process include localized absence of neuroretinal rim in an average-sized disc.

Characteristic changes in the disc are sufficiently typical that they are diagnostic of the glaucomatous process include rim-disc ratio less than 0.01 in a small disc.

A Disc Damage Likelihood Scale score of 6 or greater is a characteristic sign of disc damage. This eye has a score of 7.

Images: Spaeth GL

Suggestions of glaucomatous process

Suggestions that the glaucomatous process is present include an anterior chamber angle believed capable of occlusion but without peripheral anterior synechiae, characteristic visual field loss, IOP above 30 mm Hg, asymmetry of IOP between the two eyes greater than 30% and a central corneal thickness less than 500 µm in the presence of IOP above 28 mm Hg. These are, however, merely suggestions that the glaucomatous process is present.

Activity of glaucomatous process

Simply because the glaucomatous process is present does not mean that it is active or that the person will get worse. The process can be active, quiescent or covertly developing (in such an early stage that it is not yet detectable). To give proper care requires knowing the activity of the glaucomatous process.

If it is quiescent, then treatment is unnecessary. Activity of the process is shown by a variety of signs, including a progressive narrowing of the disc rim, extension of rim absence, a deteriorating visual field when there is no other cause for deterioration except glaucoma and worsening symptoms attributable to glaucoma. A change in the DDLS score of two units or more is diagnostic in this regard. It may be possible in the future to know that a definite deterioration has occurred based on particular amounts of change in the parameters of the various image analysis devices. When IOP is 40 mm Hg or above, it is highly likely that the process is active. Additionally, activities shown by a marked, typical deterioration of the visual field are almost certainly due to glaucoma. Such marked changes are uncommon, however. The common, minimal changes, even when considered by “the computer” to represent change, are rarely sufficiently noted to use as the basis for treatment. Last, a reliable, worsening history is important to establish.

Indicators that the glaucomatous process is present but quiescent include the combination of definite existing damage (such as a DDLS score of 7 or greater) in the absence of any symptomatic deterioration, as described by a patient able to give a reliable history; absence of change in the disc or visual field over a period of at least 5 years; and stability of IOP, in which there has been an increase of less than 20% from baseline over a period of 3 years.

Modifying factors

A variety of factors may help make the glaucomatous process express itself. These are often called risk factors, but I prefer to call them modifiers. These include a positive family history of visual loss, certain ethnic characteristics such as being of black African descent, central corneal thickness less than 500 µm, associated entities such as pigment dispersion syndrome and exfoliation syndrome, certain molecular biological characteristics, a disc that is severely damaged in the range of a DDLS score of 7 or greater, and blood pressure lower than 100/60 mm Hg.

Is disability already present?

Because the goal of treatment is the prevention of disability or the prevention of any increasing disability, searching for disability is an essential part of the evaluation of the patient. Indicators that the glaucomatous process has caused disability come primarily from the history, but also from the evaluation of the optic disc and to a lesser extent the visual field. When the disc is severely damaged (DDLS score of 8 or greater), there will always be some decrease in the person’s ability to function. The person may not be aware of this and may not complain of this until the disability has been pointed out. Correlations between visual field loss and functional ability are poor, and visual field indices are variable, so that is not a reliable indicator of the amount of disability until the field loss is extreme.

The evaluation of the visual field is an essential part of understanding a patient with glaucoma, and the findings must be interpreted with caution. There are no visual field changes that are completely specific for glaucoma, although defects that respect the horizontal meridian are often highly suggestive. Additionally, patients may have a deterioration in their visual field due to a variety of other causes, such as a retinal vein occlusion or optic nerve compressive lesion, and these may mimic the changes that occur in patients with glaucoma. In this regard, some patients with unquestionable glaucoma also develop additional causes for field deterioration, such as retinal vein occlusions, optic nerve compressive lesions and other causes for progressive visual field damage.

Conversely, fields can deteriorate markedly without any corresponding change in the printed-out visual field. Areas that already show on the printed-out field chart as zeros cannot be depicted as below zero, yet that zero does not mean that the field loss is absolute. Vision can be and frequently is still present in an area that has been designated as zero; larger, brighter objects may be visible, perhaps even just slightly larger or brighter than used as part of a test. But because that slightly brighter or slightly larger test object was not employed, the person being tested does not see the object, which is then reported as a zero. Later the patient may lose the ability to see that slightly larger or slightly brighter object and yet be able to see a still larger or brighter object, etc. Thus, patients can have serious deterioration of visual fields that are not picked up by perimetric testing as performed in most physicians’ offices. Finally, evaluation of the visual field is difficult, as has been pointed out by a variety of authors. Visual field findings, as important as they are, are best used as confirmatory evidence of changes in the optic disc or in the history.

The rate of deterioration in patients with glaucoma varies greatly, as does the shape of the curve of change. There is remarkably little known about this rate of change or the forms that the curve of change assumes. Grant and Burke showed that after 20 years, 30% of glaucoma patients were blind in one eye. In a study by Hattenhauer and colleagues, after 20 years 54% were unilaterally blind and 22% bilaterally blind. In contrast, Chen found 6% to be bilaterally blind after 15 years, and Eid and colleagues noted 8% to be unilaterally blind after 19 years. The rate of field progression is highly variable. These figures only hint at the great variability of the course of glaucoma, sometimes progressing rapidly within months and at other times showing minimal change after 15 years. Consequently, in order to get any meaningful estimate of the rate of change in a particular patient with glaucoma, the nature of the clinical course must be developed individually for each patient.

The rate of change is obviously important when one is interested in determining where the glaucomatous process is going to lead the patient. Furthermore, it has been shown by Caprioli’s group that when the rate of change is rapid, rate of change of visual field is an accurate predictor of what will happen in the future.

Further thoughts on disability

To determine the destination at which a person will arrive requires knowing where she is, how fast she is going and how long she will travel. Similarly, to determine what will happen to a patient with glaucoma requires knowing 1) the amount of damage that is already present, 2) the rate of change, 3) the direction of change (better or worse), and 4) an estimate of how long the change is expected to continue; for most types of glaucoma this usually means the patient’s remaining years of life, although there are obvious exceptions, such as steroid-induced glaucoma.

Estimating life expectancy (the remaining years expected) cannot meaningfully be done using averages, any more than can estimating the rate of change by using averages. Data points can be safely and validly used to establish means. Means cannot be safely or validly used to establish data points. A healthy 25-year-old person with juvenile open-angle glaucoma will probably live for 10 to 50 years, whereas a 25-year-old person with disseminated metastatic pancreatic cancer is not likely to survive for more than a year. A 75-year-old marathon runner in superb health may well continue to live for 20 years, whereas a 75-year-old person on oxygen for advanced chronic obstructive pulmonary disease who has already had three myocardial infarctions and who continues to smoke is not likely to survive for a year. Factors influencing life expectancy are shown in the Table. It is, then, essential to take into account these individual characteristics when estimating an individual’s life expectancy. Additionally, this type of calculation must be updated at subsequent visits; life expectancy might change. For example, a few individuals with metastatic pancreatic cancer may survive for many years, and a few 75-year-old marathon runners may die from massive cardiac disease a day after their visit to your office.

Colored Glaucoma Graph

One way to evaluate the present and expected significance to the patient of the glaucomatous process is to draw graphically the Colored Glaucoma Graph (Figure 5). The colors of this graph help the physician and the patient understand the significance of that particular expression of the disease. When a patient is in the green zone, with a disc that has a DDLS score of 4 or less, the patient cannot be said with certainty to have damage, unless a previous evaluation showed a disc that had a smaller DDLS score. When patients have moved from the green zone to the yellow, they have gone from being at risk to having developed definite damage, although the damage is not sufficiently severe that it has produced symptoms noticeable to the patient. Finally, those who have more advanced disease, so that they are aware that they no longer can function normally, are in the red or disabled zone. All patients already in the red zone will have a further deterioration of quality of life if they have any worsening of their glaucoma. In contrast, patients in the green zone can develop considerable damage without accruing any disability.

In order to plot the rate of change on this graph, one must have valid, feasible units on the vertical axis. Parameters derived from various image analysis instruments may in the future provide this information. At present, however, this is not yet possible. Right now ophthalmoscopic evaluation and attribution of the DDLS score provide such information. The DDLS is valid and reproducible within ±1 scale unit. Thus, a change in two units on the DDLS is not likely to occur unless there is an actual change in the disc. There must be a sufficient number of points on the graph to establish a rate of change. The physician must be aware that any line that is being drawn may well not be linear. If the line appears to be sloping rapidly downward, it is possible that the slope could increase or decrease in the future. Additionally, as mentioned, for the graph to have any value there must be a meaningful estimate as the duration of the change will continue to occur.

The Colored Glaucoma Graph is utilized daily in my practice. A copy of it is shown to the patient while his condition is being discussed and the points are being drawn in order to develop a plot of the rate of change. Where multiple points are not yet known, then a comment is made to the patient that the rate of change cannot be accurately determined. The patient is told that it is possible, for example, to identify a type of bird by looking at a still photograph, but it is not possible to tell how fast the bird is flying based on a still photograph. In the same way, it may be possible to determine whether or not the patient has a sign of glaucoma, but whether the glaucomatous process is active and how rapidly it is changing cannot be determined with certainty based on a single examination, although careful history-taking may provide valuable clues in that regard.

What the patient wants to know, unless misled by us, is the answer to, “Will I lose my vision?” or “Will I lose more vision?” Whether or not they have “glaucoma” is not their concern, although we may introduce that often unanswerable issue. It is helpful to patients to direct their concerns (and ours as physicians) to the real issue — is disability present already, and if so, can further disability be prevented, or is disability likely to develop if treatment is not employed or changed? These are the issues we need to address meaningfully with our patients.

For Your Information:

George L. Spaeth, MD, can be reached at Wills Eye Hospital, 840 Walnut St., Philadelphia, PA 19107; 215-928-3197; fax: 215-928-0166; e-mail: gspaeth@willseye.org.

References:

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