Despite the fact that there are many different types of glaucoma with different manifestations, diagnostic approaches, and treatment modalities, this chapter summarizes some of the generalizable concepts of glaucoma management. While there are probably as many approaches to glaucoma as there are different patients and different caregivers, the concepts presented here are the result of years of experience and are applicable to the extent that generalizations can be; however, they must be modified to the requirements of each patient and physician.
SYMPTOMS AND HISTORICAL INFORMATION RELATED TO THE GLAUCOMAS
Many factors in the patient’s history bear on the diagnosis and treatment of glaucoma. Most patients with glaucoma, especially primary open-angle glaucoma (POAG), chronic angle-closure glaucoma, and other chronic forms of glaucoma, are asymptomatic until late in the course of the disease. However, certain patients may have symptoms such as pain, redness, halo vision, blurred vision, and a change in the appearance of the eye. Pain associated with glaucoma is related to the height of the intraocular pressure (IOP) and the rapidity with which it rises to that level. Conditions that cause rapid and sustained rises of IOP to high levels, such as acute angle-closure glaucoma, are often accompanied by pain. Conditions such as POAG that cause less dramatic changes in IOP are usually not associated with pain. Occasionally young patients with open-angle glaucoma (e.g., pigmentary glaucoma) may experience discomfort when IOP rises rapidly even to moderate levels. Other mechanisms for pain in glaucoma include inflammation, bullous keratopathy, and drug-induced side effects (e.g., miotic-induced ciliary and orbicularis muscle spasm). In angle-closure glaucoma or glaucoma associated with acute iritis, conjunctival injection may take the form of a ciliary flush. Other causes of red eyes in glaucoma patients include prostaglandin-like agents, other drug reactions, allergic conjunctivitis, endophthalmitis, neovascular glaucoma, hyphema, subconjunctival hemorrhage, bullous keratopathy, and increased episcleral venous pressure.
When IOP rises rapidly, the corneal endothelium may not be able to adequately pump fluid from the cornea – resulting in edema of the epithelium and, sometimes, the stroma. This condition may produce a visual sensation of colored halos around incandescent lights. Episodic blurring of vision is often noted when rapid elevations of IOP cause corneal edema. It is important to remember that many patients refer to uncolored semicircular or radiating images as halos. This distortion in vision may be caused by opacities in the media, uncorrected refractive errors, and alterations in the tear film. In these latter conditions, the ophthalmologist can often elicit ‘halo’ vision in the office while the IOP is normal and the cornea is clear.
Glaucoma can alter vision in a number of other ways. Occasionally a patient may note a diminished visual field during some activity that requires monocular vision (e.g., aiming a rifle, looking through a camera). Patients with asymmetric vision loss may not be aware of their defect until they close the better eye. Loss of Snellen visual acuity usually occurs late in the course of glaucoma unless some other problem occurs, such as central retinal vein occlusion. However, loss of color perception, motion perception, contrast sensitivity, temporal contrast sensitivity, vernier acuity, and other visual functions may occur much earlier in the disease than previously thought; patients may be aware of these subtle changes and complain about them even when visual acuity and standard visual fields are normal.
A few patients may complain of a change in the appearance of the eye which may come from exophthalmos, haziness of the cornea, or an alteration in pupil size, shape, or position.
A careful medical history may provide important information related to glaucoma. The medical history should include the following points:
Ocular history should include queries about amblyopia, trauma, inflammation, surgery, cataract, retinal detachment, and inflammation. If not questioned directly, patients may not remember a ‘trivial’ eye injury that may have occurred many years ago.
General medical history should focus on obtaining information about vascular diseases (e.g., hypertension, diabetes, cardiac problems, hypotensive episodes) that might affect ocular perfusion, or other conditions that could mimic or aggravate glaucomatous visual field loss (e.g., demyelinating diseases, central nervous system tumors, or aneurysms). A history of migraine or other vasospastic disorders is important to elicit, particularly for ‘normal-pressure’ glaucoma. The clinician must know about the patient’s general health before prescribing medication or considering surgery. For example, topical β-blocker agents can exacerbate asthma or congestive heart failure.
The patient’s medication history and allergies should also be documented. Many drugs (e.g., corticosteroids or anticholinergic agents) can alter IOP and affect the course of glaucoma. Conversely, many ocular medications can induce or aggravate systemic medical problems. Frequent exchange of information between the ophthalmologist and the family physician is important. A history of sulfa allergy may make the use of carbonic anhydrase inhibitor therapy unwise unless no other alternative is available.
The presence of a family history of ocular diseases – especially glaucoma, but also including cataract, strabismus, amblyopia, and retinal problems – should be determined. Many glaucoma conditions are familial, and information about family members may aid diagnosis and treatment.
Furthermore, now that certain kinds of glaucoma have been related to specific gene abnormalities, elicitation of the family history and even pedigree may be very important for the patient and his or her siblings and offspring. Often, the patient may be aware of some familial eye problem but not be able to specifically identify it. Even in families with severe, blinding, genetic glaucoma, as much as one-quarter of the relatives may be unaware of the condition.
The ocular examination should include measurement of best visual acuity; an evaluation of the adnexa for exophthalmos, signs of trauma, or inflammation, and assessment of motility for signs of restriction or paresis. The pupil should be evaluated for size, shape, and reactivity. The slit lamp should be used for assessment of the cornea for epithelial, stromal, and endothelial abnormalities, and for anterior synechiae. The slit lamp should also be used to assess the iris for atrophy, growths, or blood vessels; the anterior chamber for depth and clarity, and the lens and vitreous for clarity. The IOP should be measured before dilation or gonioscopy. The examination should also include a careful evaluation of the retina and its vessels, the macula, and the optic nerve. The status of the optic nerve should be documented periodically, preferably by an objective method such as photography or another imaging technique. Careful descriptions or drawings are acceptable if photography or digital imaging is not available. The nerve fiber layer should be evaluated both for generalized thinning and for localized defects. Gonioscopy is indicated whenever the diagnosis of any kind of glaucoma is suspected. A visual field examination should also be undertaken either for baseline or for follow-up. Corneal thickness (pachymetry) should be ascertained in all open-angle glaucoma suspects and probably, at least once, in all glaucoma patients since thin corneas are a risk factor for progression to glaucoma from ocular hypertension and may help in determining target pressure ranges.
Several risk factors are known to contribute to the development of glaucoma, its progression or lack thereof, and its extent. The known factors include heredity, ethnicity, the size of the eye (small for angle closure, large for open angle), the presence or absence of systemic vascular disease, vasospastic disorders including migraine, and the size and shape of the optic cup (see Table 21-1 ). Although elevated IOP is a major risk factor, it is not the only one and is not, in and of itself, enough to account for all of the damage unless it is very elevated. As noted above, a thin cornea is a significant risk factor for development of open-angle glaucoma among ocular hypertensive eyes.
|Mild||0.0–0.5 with uniform pink rim||None, mild depression, or slight defect|
|Moderate||0.6–0.7 with some local narrowing of rim||General depression, arcuate defect, or paracentral scotoma|
|Advanced||0.8–0.9 with rim narrowing or notching||Large arcuate, double arcuate, hemifield loss, or fixation threatened|
People of black African descent have a much higher risk of developing open angle glaucoma and of becoming blind as a result of it. People of Hispanic descent also have a somewhat higher risk of open-angle glaucoma. Individuals descended from certain south-east Asian peoples, such as Chinese and Vietnamese, have a higher rate of angle-closure glaucoma than Caucasians; included in this group are some indigenous Americans.
If glaucoma is thought of as a disease that damages the structural and/or functional integrity of the eye and can often be slowed or arrested by lowering IOP, then decisions are simplified. Those patients who have structural or functional damage either caused by pressure or affected by pressure should be treated. In most instances, the damage is fairly obvious, in the form of visual field loss, classic disc cupping, nerve fiber layer defects, corneal edema, arterial pulsations, or sometimes pain. Usually IOP is above the statistically normal range, so glaucoma is easy to diagnose. Once the disease is diagnosed, the decision to treat is simplified.
In other situations, things are not quite so simple. There may be questionable damage with normal pressure, or there may be elevated pressure without damage. These patients are glaucoma suspects and can be divided into four categories, depending on the level of IOP, the evidence of damage, and the presence of other risk factors.
IDENTIFYING GLAUCOMA SUSPECTS
The purpose of identifying someone as a glaucoma suspect is to be able to monitor that individual for the earliest sign of damage and, by intervening at that point, to prevent any visually significant damage from occurring in that person’s lifetime. This approach has the advantage of withholding treatment from those who may never need it. Thanks to the Ocular Hypertension Treatment Study (and later the European Glaucoma Prevention Study) we can now identify ocular hypertension patients who are at greatest risk of developing glaucoma and, perhaps, in these highest risk patients, begin treatment even before serious damage has occurred to the optic nerve. Actual risk calculators have been worked out and validated to determine the relative risk of developing glaucoma from ocular hypertension.
Although some patients have progressive glaucomatous damage with no recorded IOPs above 21 mmHg, other patients have IOPs frequently above 21 mmHg without exhibiting glaucomatous damage. The 21-mmHg mark remains useful for classifying glaucoma suspects for two reasons. First, 21 mmHg represents 2 standard deviations above the mean IOP of 16 mmHg in white populations. Pressure above this would occur in only 2.5% of normal cases if IOPs were indeed distributed normally in the population. Actually, the distribution of IOP is skewed to the right, so that 4–5% of ‘normal’ patients may have pressures higher than 21 mmHg. Although this is a small percentage of the normal patients, the actual number of patients with elevated IOP who never develop damage far exceeds the number of those who do develop damage. Therefore the chance of requiring treatment when only elevated IOP is present (<30 mmHg), with no other risk factors, is probably less than 10%. Second, elevated pressure can cause glaucomatous damage. This is certainly true in experimental animals. The higher the pressure, the more rapidly the damage progresses. If the damage has not progressed too far, it can be arrested in many cases by adequate lowering of the IOP. Thus elevated IOP is an important risk factor and must be taken seriously.
Anatomic signs may also make someone suspicious for glaucoma. Signs include the presence of narrow angles, an enlarged but not definitely pathologic optic cup, and thinning of or defects in the nerve fiber layer. Functional signs such as early but not definite visual field changes could also place someone in the suspect category. Color vision deficits may also herald the onset of glaucomatous damage. Finally, hereditary or genetic information – such as a strong family history of glaucoma or possession of a gene associated with glaucoma, as well as other high-risk factors such as race or high myopia, even in the absence of elevated IOP or increased cupping – warrants closer observation than the general population. Table 21-1 lists the risk factors for primary open-angle glaucoma.
Damage to the optic nerve is central to the diagnosis of glaucoma. Damage to the functional or structural integrity of the eye that is typical of glaucoma may be absent, questionably present, or present. If it is present, the patient either has or has had glaucoma or some disease that mimics it. If it is absent or questionably present, the patient may have glaucoma. Usually, the dilemma arises when trying to recognize early optic nerve or visual function damage typical of POAG.
If a patient is a glaucoma suspect, the ophthalmologist must decide whether to treat or to observe the patient. That decision usually is based on both the physician’s judgment of the amount of risk to the patient if left untreated and the patient’s anxiety about the condition (or about medications). Boxes 21-1 through 21-4 list some examples of various types of glaucoma suspects and their management. Signs indicative of disc or field damage are listed in Box 21-5 . The purpose of observing the glaucoma suspect is to recognize any evidence of early damage. If damage progresses, then the presence of glaucoma (or other optic neuropathy) has been proven, and treatment must commence or be escalated.
Normal intraocular pressure, no damage
Strong family history of glaucoma
Retinal vascular occlusion
Pigmentary dispersion syndrome
History of halos
Management: monitor periodically and inform patient of need for follow-up.