eMedicine Specialties > Ophthalmology > Intraocular Pressure

Glaucoma, Suspect, Adult

Author: Robert H Graham, MD, Senior Associate Consultant, Department of Ophthalmology, Mayo Clinic, Scottsdale, Arizona
Contributor Information and Disclosures

Updated: Mar 19, 2009

Introduction

Background

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.

Pathophysiology

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. 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.

Frequency

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.^8,9 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.

Mortality/Morbidity

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.

Race

• 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.¹⁰
• Asians, Canadians, Alaskans, Greenland Inuit Indians, and certain South American Indians are at an increased risk for narrow-angle glaucoma.

Sex

• No sexual predilection exists for POAG.
• Women are at a greater risk for angle-closure glaucoma than men.

Age

• 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).

Clinical

History

• 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^11,12 :
  • Myopia
    • Risk factor for glaucoma
    • Disc evaluation difficult (myopic fundus, tilted disc)
    • Visual field testing more difficult (fundus abnormalities, refraction-related inaccuracies)
  • Pseudoexfoliation - Increases with advanced age
  • Pigment dispersion (25-50% risk of developing glaucoma)
  • Ocular trauma
  • Glaucoma in one eye
    • Associated with increased risk of future damage in the other eye
    • Development of visual field defects in an average of 5 years in about 29% of untreated undamaged fellow eyes
  • History of uveitis/inflammatory ocular disease
  • Congenital anomalies
  • Prior eye surgery
  • Retinal vascular occlusion - In individuals who are susceptible, increased IOP is associated with a risk of developing central retinal vein occlusion (CRVO).
  • Current or past use of steroids
    • Topical steroids may elevate pressure in certain individuals.
    • Optic nerve damage may be residual from previous increased IOP associated with steroid use.
    • The elevation of IOP is usually seen within a few weeks of starting topical steroids.
• Systemic history includes the following conditions that have been associated as risk factors for developing glaucoma^11,12 :
  • Low blood pressure - Also includes overmedication of systemic hypertension
  • A previous episode of hypotensive shock, trauma, vascular surgery, or hemorrhage can be significant; it may indicate that optic nerve damage is not progressive but may have been a onetime insult.
  • History of vasospastic disorders - A higher prevalence of migraine headaches and Raynaud syndrome exists with normal-tension glaucoma.
  • Medications
    • In individuals who are susceptible, steroids may cause a rise in IOP.
    • Anticholinergics (antihistamine and antipsychotics) may precipitate angle-closure glaucoma.
  • Cardiovascular disease may be a factor in low-tension glaucoma.
  • Hypertension
  • Diabetes mellitus
    • Small association
    • Some studies have reported a higher prevalence of increased mean IOP and POAG with diabetes mellitus.
    • Diabetes is a questionable risk factor for glaucoma. The association may be a result of self-selection into the health care system.
• 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:
    • POAG - Juvenile onset; genetic linkage mapped to band 1q23¹³
    • POAG - Adult onset^14,15
    • Pigmentary glaucoma - Gene responsible for fragment dispersion syndrome mapped to band 7q35q36¹⁶
    • Pseudoexfoliation
    • Aniridia
    • Axenfeld-Rieger syndrome
    • Primary congenital glaucoma
• 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.)

Physical

• IOP
  • IOP is a definite and important risk factor for developing glaucomatous damage but is not sufficient for a diagnosis.^17,18,12,19
    • 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.
  • Diurnal variation
    • 2-6 mm Hg - Normal
    • Greater than 10 mm Hg - Variation suggestive of glaucoma
  • Peak usually occurs in the morning hours.
  • IOP measurement
    • Goldmann-type applanation tonometry is the criterion standard.
    • In patients who are obese, handheld tonometry may be more accurate by minimizing strain to fit to the slit lamp.
  • Common pitfalls in IOP measurement
    • Too much/too little fluorescence occurs.
    • Meridians are not averaged in patients with high astigmatism.
    • The upper lid is not held gently.
    • Patients should breathe normally.
    • Unless dangerously elevated, IOP is checked numerous times before initiating treatment to assess diurnal variation.
    • Abnormally thick corneas may result in artificially high IOP measurements by applanation tonometry, while abnormally thin corneas may result in artificially low IOP measurements.
• Corneal pachymetry
  • The Ocular Hypertension Treatment Study (OHTS) showed central corneal thickness as a significant predictor of the development of POAG.^8,17
  • 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.
• Slit lamp examination - Look for signs of secondary causes/risk factors of glaucoma.
  • Corneal endothelium
    • Krukenberg spindle
    • Keratic precipitates
    • Pigmentary changes on endothelial cells
  • Anterior chamber angle depth
    • Identification of narrow occludable depth
    • Avoidance of mydriatics in such eyes
  • Iris
    • Mid iris spokelike transillumination defects (seen in pseudoexfoliation and pigment dispersion)
    • Dandrufflike material on pupillary margin and on lens capsule (pseudoexfoliation)
    • Neovascularization
• Gonioscopy - Perform on all patients who are glaucoma suspect, and repeat it periodically. It is especially important in the following cases:
  • The chamber shallows, and IOP rises.
  • Angle problems (eg, hyperopia, symptoms of subacute/acute angle-closure glaucoma, narrow angle) are evident.
  • The patient is diabetic.
  • Vein occlusion is present.
  • A history of ocular trauma exists.
• Evaluation of angle depth, signs, and risk factors for secondary glaucoma
  • Narrow-angle depth
  • Angle recession
  • Heavy pigmentation of TM (pigment dispersion)
  • Patchy pigmentation of TM (pseudoexfoliation)
  • Hemorrhage
  • Inflammatory changes
  • Angle closure
  • Peripheral anterior synechiae
  • Neovascularization of the angle
• Evaluation of the optic nerve head^20,21
  • 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.
    • High magnification
    • Stereoscopic view
    • Excellent illumination
    • Special attention to contour and color
  • 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.²²
    • 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.²³
    • Generalized enlargement of cup
    • Focal notching
    • Superficial splinter hemorrhage
    • Asymmetry of cupping between 2 eyes
    • Nerve fiber layer dropout
    • Asymmetry of neuroretinal rim
    • Focal thinning of neuroretinal rim
    • Acquired change in disc rim appearance
    • Acquired change in retinal nerve fiber layer
    • Nerve fiber layer deficit
    • Thinning of inferior-temporal rim
    • Progressive enlargement of cup
    • Vertical elongation of cup
    • Cupping to rim margin
    • Exposure of lamina cribrosa
    • Peripapillary atrophy
    • Baring of circumlinear vessels
  • Search for other abnormalities that may account for the visual field defect.
    • Tilted disc
    • Disc drusen
    • Optic pits
    • Retinal disease
    • Optic atrophy
  • Document the appearance of the optic nerve head.
    • The preferred technique - Baseline stereo disc photographs for future comparison
    • Detailed description and drawings
    • Automated techniques
      • Scanning lasers - Advantages include accurate, reproducible, and patient comfort (nondilated). A disadvantage is the cost (expensive).
      • Polarimetry - Advantages include accurate and reproducible. A disadvantage is the cost (expensive).
• Evaluation of the retinal nerve fiber layer - Look for nerve fiber layer defects/dropout.
  • Techniques
    • Ophthalmoscopic examination with red-free (green) filter
    • Good color photography
    • Red-free photography
  • Instruments for retinal nerve fiber layer analysis²⁴
    • Advantage - Most accurate
    • Disadvantage – Expensive
• 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
    • Pupillary diameter should be maximized.
    • Correct refraction should be used.
    • Patient reliability is limited in some cases.
  • 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.^25,26 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. Takes 4-5 minutes for each eye; screening test takes less than 1 minute. Potential role exists in diagnosing early glaucoma and in detecting moderate-to-advanced glaucoma.²⁷

Causes

• Risk factors that are associated with developing glaucomatous damage include the following:
  • Elevated IOP
  • Suspicious optic nerve head appearance
  • Nerve fiber layer defects
  • Increasing age
  • Family history of glaucoma
  • African American ethnicity
  • Myopia
  • Diabetes mellitus
  • Pseudoexfoliation
  • Pigment dispersion
  • History of ocular trauma with associated angle recession
  • History of uveitis
  • Glaucoma in one eye
  • Narrow anterior chamber angle depth
  • Prior eye surgery
  • Steroid use
  • Migraine headache
  • Cardiovascular disease
• 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.

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