Glaucoma suspect describes a person with one or more risk factors that may lead to glaucoma, but this individual does not have definite glaucomatous optic nerve damage or visual field defect. A great overlap can exist between findings in patients with early glaucoma and those who are glaucoma suspect without the disease.[1, 2, 3] Five to 10 million Americans with ocular hypertension have elevated intraocular pressure (IOP) above 21 mm Hg without evidence of damage. Many of these patients are being treated, but the indications for treatment are not clear-cut. Many others are glaucoma suspect based on the suspicious appearance of the optic nerve head or other risk factors.
With an earlier accurate diagnosis and timely therapy, the goal for this century should be to prevent glaucoma-related blindness. For example, during Glaucoma 2001, a public service project of the foundation of the American Academy of Ophthalmology, individuals with sufficient risk factors that make them susceptible to glaucomatous visual loss were identified and evaluated. The goal of identifying and treating patients who are glaucoma suspect is to preserve visual function by monitoring them for the earliest signs of glaucomatous damage. In individuals who are at a high risk of developing glaucomatous damage, preventive measures, including lowering IOP, may be indicated.
The mechanisms that cause glaucoma are not fully understood. In most clinical cases, a painless elevation of IOP occurs, which can lead to progressive optic nerve damage and visual field loss.[4] The mechanical theory of resistance to outflow (at the juxtacanicular meshwork) is one postulated mechanism for glaucoma. Disturbances of trabecular meshwork (TM) collagen, TM endothelial cell dysfunction, basement membrane thickening, glycosaminoglycan deposits, narrowing intertrabecular spaces, and/or collapse of the Schlemm canal may occur. Experimental and clinical studies show that sustained elevation of IOP can cause optic nerve damage similar to primary open-angle glaucoma (POAG), thus providing support for the role of IOP.
Vascular risk factors and the role of optic nerve perfusion may be of importance.[5] The blood supply to the optic nerve, the axonal or ganglion cell metabolism, and the lamina cribrosa extracellular matrix may play a role. This is especially important in a subgroup of individuals with low-tension glaucoma who have progressive disease despite IOP of less than 21 mm Hg.
Susceptibility of the optic nerve to damage varies from individual to individual.[6, 7] Along with other risk factors, it also depends on the level of IOP. Certain historical and demographic factors, including age, race, family history, and past ocular history, have been shown to have a high association for the disease. Even sleeping position may play a role; Sedgewick et al have shown that lateral and prone sleeping positions result in a significant IOP elevation in patients with pigment dispersion.[8]
Congenital variations, especially in the appearance of the optic nerve or a onetime vascular insult, may be the underlying etiology for a patient's findings and subsequent diagnosis of glaucoma suspect. The key is whether any progression occurs.
United States
Elevated IOP (ocular hypertension) is estimated to affect 5-10 million Americans, placing them at risk for developing glaucomatous damage. Each year, about 1% of individuals with ocular hypertension develop glaucomatous damage. Similarly, many patients with other risk factors, such as suspicious optic nerve appearance, nerve fiber layer defects, and family history of glaucoma without definite glaucomatous damage, are observed.[9, 10] More than 7 million office visits occur per year to monitor patients with glaucoma or to observe those who are glaucoma suspect.
International
More than 100 million people have elevated IOP. More than 3 million people worldwide are blind secondary to POAG; about 2.4 million people develop POAG each year.
Glaucoma is the second most common cause of legal blindness (described as visual acuity [VA] of 20/200 or poorer and visual field of less than 20° in width of its diameter) in the United States, and it is the leading cause of blindness in African Americans. Between 80,000-116,000 persons are legally blind secondary to glaucoma. Each year, an additional 5,500 people are estimated to become legally blind. At least 2.25 million people older than 40 years have glaucoma, but only one half are aware of it and are being treated. As an example, in the United States in 1977, $400 million was spent on direct health costs related to glaucoma; $1.3 billion was lost because of decreased productivity.
African Americans have a significantly increased risk for developing POAG. The prevalence of POAG is 3-6 times higher in African Americans than in whites. Glaucoma usually occurs earlier in African Americans than in whites. African Americans not only are 4-8 times more likely to become blind but also go blind 8 times faster.[11]
Incidence of OAG in Latinos is higher than in non-Hispanic whites, but lower than in Afro-Caribbeans.[12]
Asians, Canadians, Alaskans, Greenland Inuit Indians, and certain South American Indians are at an increased risk for narrow-angle glaucoma.
No sexual predilection exists for POAG.
Women are at a greater risk for angle-closure glaucoma than men.
Increasing age is a definite risk factor.
The risk of POAG increases with advancing age.
The prevalence of POAG is 3-10 times higher among individuals older than 80 years (than people in their 40s).
Most patients who are glaucoma suspect do not develop glaucomatous optic nerve damage and/or visual field loss. Overall, about 1% of individuals with ocular hypertension develop glaucoma per year. The risk is higher for patients with additional risk factors.
Glaucoma causes silent damage; follow-up care is essential to exclude any progressive change over time that may warrant treatment.
Left untreated, patients with optic nerve damage may progress, resulting in progressive loss of side vision and eventually total optic nerve atrophy and irreversible blindness.
Patients should be educated regarding their risk factors, prognosis, and the importance of follow-up care. Glaucoma can cause silent damage with eventual vision loss.
For excellent patient education resources, visit eMedicineHealth's Eye and Vision Center. Also, see eMedicineHealth's patient education articles Adult Glaucoma Suspect, Glaucoma FAQs, Normal-Tension Glaucoma, and Ocular Hypertension.
Patients do not usually experience any symptoms. Intermittent headaches, haloes, and blurred vision may suggest risk for angle-closure glaucoma.
Ocular history includes the following ocular conditions that have been implicated as risk factors for developing glaucoma[13, 14] :
Systemic history includes the following conditions that have been associated as risk factors for developing glaucoma[13, 14] :
Family history is a definite risk factor. Heritable susceptibility has been shown. Between 10-20% of patients with glaucoma have a positive family history. Ask about family history of glaucoma, especially in first-degree relatives. Family history of glaucoma in a sibling is the greatest risk factor, followed by glaucoma in a parent. Also, ask if glaucoma in other family members resulted in vision loss (the individual may have only had ocular hypertension). The Baltimore Eye Survey found that the relative risk of having glaucoma is increased 3.7-fold for individuals who have siblings with POAG.
Heritable susceptibility (genetics of glaucoma) has been shown for the following:
Review of old records: Note previous IOP, cup-to-disc ratios, ocular surgery, and past visual fields. (Caution: Poor agreement and observer variability can occur in disc examinations over time.)
Elevated IOP is a definite and important risk factor for developing glaucomatous damage but is not sufficient for a diagnosis.[20, 21, 14, 22] The prevalence of POAG is higher with increasing IOP. One tenth of patients with ocular hypertension develop field loss within 10 years. Each year, about 1% of all individuals with increased IOP progress to glaucomatous damage. As many as 50% of patients with glaucomatous optic neuropathy or visual field changes have IOP of less than 21 mm Hg on initial evaluation. Some eyes undergo damage at IOP of less than 18 mm Hg; others tolerate IOP of more than 30 mm Hg.
A pressure of 10-21 mm Hg is considered normal; a nongaussian distribution occurs with a skew toward higher pressures.
The diurnal variation is as follows:
Peak usually occurs in the morning hours.
Goldmann-type applanation tonometry is the criterion standard for IOP measurement. In patients who are obese, handheld tonometry may be more accurate by minimizing strain to fit to the slit lamp.
Landers et al proposed an ibopamine challenge test to differentiate patients who are glaucoma suspect from those who have either stable glaucoma or progressive glaucoma.[23]
Common pitfalls in IOP measurement are as follows:
The Ocular Hypertension Treatment Study (OHTS) showed central corneal thickness as a significant predictor of the development of POAG.[9, 20]
Patients with a central corneal thickness of less than 555 µm had a 3 times greater risk of developing POAG than patients with a central corneal thickness of greater than 588 µm.
Look for signs of secondary causes/risk factors of glaucoma, as follows:
Perform on all patients who are glaucoma suspect, and repeat it periodically. It is especially important in the following cases:
Examine for the following:
The best examination method is a slit lamp combined with a 60-D, 78-D, or 90-D Hruby lens or a posterior pole lens through a dilated pupil, which offers the following benefits:[24, 25]
The normal vertical cup-to-disc ratio is 0.3. In a normal rim, the inferior portion is thickest, followed by the superior rim. Patients with myopia have larger eyes and larger discs and cups. Assessing optic nerve damage in small optic discs with minimal cupping may be difficult.[26] Large optic discs may appear pathologic when they actually show only physiologic cupping, especially in African Americans.
Signs of early glaucomatous damage can be subtle, as follows:[27]
Search for other abnormalities that may account for the visual field defect, as follows:
Document the appearance of the optic nerve head. The preferred technique is baseline stereo disc photographs for future comparison. Detailed description and drawings should be obtained.
Automated techniques are as follows:
Look for nerve fiber layer defects/dropout.
Techniques are as follows:
Instruments for retinal nerve fiber layer analysis are very accurate, but they are expensive.[29] Sehi et al have shown that progressive atrophy of the retinal nerve fiber layer has been associated with subsequent visual field loss.[30] Miki et al found that faster retinal nerve fiber layer thinning corresponded to an increased risk of developing visual field defects.[31]
Results of visual field testing should be normal.
Absence of visual field defects does not ensure absence of glaucoma.
As many as 50% of optic nerve fibers in a single optic nerve may be damaged before visual field defects are found by Goldmann perimetry.
Common pitfalls in visual field testing are as follows:
Interpretation of visual field testing: Use comparable tests when comparing fields. For example, one cannot directly compare Swedish interactive thresholding algorithm (SITA) with Fastpac or HVF 30-2 threshold testing. If a field defect is detected, ensure that it is reproducible. The abnormal points should be contiguous, paralleling the pattern of the nerve fiber layer in an arcuate pattern respecting the horizontal midline. The greater the abnormal points and the deeper the defects, the more likely it represents a true scotoma.
The standard testing strategy used by many ophthalmologists in past evaluations has been HVF 30-2 or 24-2 traditional threshold testing with statistical analysis.
Humphrey Fastpac requires less testing time; decrease in precision of threshold algorithm estimate.
SITA reduces testing time by about 50% without sacrificing accuracy. Less interindividual variability occurs, and gray scale printouts may look lighter.
Short wavelength automated perimetry (SWAP) uses blue target on a yellow background to isolate those visual pathways that are believed to be damaged selectively in early glaucoma. Many studies suggest that it is capable of earlier detection of glaucomatous defects, which may be useful in detecting progression to glaucoma in those patients who are glaucoma suspect and at a high risk.[32, 33] It requires longer testing time with 3-minute adaptation to yellow background.
Frequency-doubling technology perimetry uses a coarse striped grating of rapidly alternating dark and light bands. It takes 4-5 minutes for each eye; screening test takes less than 1 minute. A potential role exists in diagnosing early glaucoma and in detecting moderate-to-advanced glaucoma.[34] Liu et al suggest that frequency-doubling technology is effective in monitoring visual field progression and that it may detect field defects earlier than standard automated perimetry.[35]
Risk factors that are associated with developing glaucomatous damage include the following:
The greater the number and the degree of risk factors, the greater the risk of developing glaucoma over time.
Some risk factors, such as pigment dispersion, increased IOP, suspicious optic nerve head appearance, increasing age, glaucoma in one eye, pseudoexfoliation, a strong family history of glaucoma, and race (ie, African American), are more important than other factors.
Start treatment if documentation of progression to glaucoma with optic nerve damage and/or reproducible visual field defect exists. The initiation of ocular hypotensive medication among glaucoma suspects significantly reduced the velocity of VF progression.[37]
Ocular hypertension with pressure-lowering medication may delay or prevent subsequent development of glaucomatous damage. The OHTS, a large multicenter clinical trial sponsored by the National Eye Institute, studied this possibility. The OHTS concluded that for individuals with ocular hypertension at significant risk for developing glaucoma, topical ocular hypotensive medications were effective in delaying or preventing the onset of primary open-angle glaucoma (POAG).[20, 38, 39]
In general, most ophthalmologists treat patients with IOP of greater than 30 mm Hg.
Carefully weigh the likelihood that the patient's risk factors will contribute to glaucomatous optic nerve damage against the ocular and systemic risks that are associated with possible treatments.[40] Lim et al found that 2.6% of normal-tension glaucoma suspects progressed to glaucoma per year, with higher baseline IOP and thin average retinal nerve fiber layer being risk factors for progression.[41]
The decision to treat a patient who is glaucoma suspect and at high risk is individualized, considering the following: the risks and the rate at which glaucomatous damage and decreased visual function can occur, the patient's desires, expected longevity, and tolerance of treatment.
Other factors, such as reliability of visual field testing, availability of follow-up visits, and ability to examine the optic disc, may contribute to starting treatment.
If an ophthalmologist decides to treat a patient who is glaucoma suspect and at high risk, using one or more topical antiglaucoma agents to lower the IOP may be preferable.[42] The adverse effects, the profile, and the frequency of use should be weighed against the patient's ocular and medical histories. Animal data are available that suggest that Alphagan, Xalatan, or Betoptic may play a role in improving optic nerve perfusion.
In patients with very shallow, occludable anterior chamber angle depth, laser peripheral iridotomy can be a preventive measure in decreasing the risk of acute angle-closure glaucoma.
Laser trabeculoplasty is infrequently indicated for treating patients who are glaucoma suspect. In patients with POAG and OHT, the percentage of IOP reduction after SLT was significantly greater in eyes with thinner corneas (CCT < 555 μm), indicating patients with thinner corneas had better IOP control after SLT.[43]
Filtering procedures are generally reserved for patients with documented glaucomatous optic nerve damage.
The frequency and the composition of follow-up evaluation depend on the age of the patient, the level of elevation of IOP, the appearance of optic nerve head cupping, a family history of glaucoma, the presence of additional risk factors, and the stability of the patient's clinical course.
In general and depending on the patient's risk factors, check IOP every 3-12 months. If the patient is a low-tension glaucoma suspect with normal IOP but suspicious optic nerve head cupping, conduct a diurnal assessment of IOP.
Perform visual field examinations every 6-12 months. If a new visual field defect is suspected, the test should be repeated (preferably within 1 mo) to ensure that the defect is reproducible.
Gonioscopy and optic nerve head evaluation are generally performed annually.
Baseline documentation, such as stereo disc photographs, should be obtained for future comparison to objectively evaluate any possible subtle progression. In selected patients, some ophthalmologists prefer to obtain this documentation yearly for detailed comparison.