Open Angle Glaucoma

See Also

Epidemiology

Most common type of Glaucoma (89%)
Lifetime Prevalence: 10% of U.S. population (50% are unaware of diagnosis)
More common in older patients
1. Rare under age 40 years
2. Prevalence among those over 80 years old: 14%
3. However most undiagnosed Glaucoma is at age <60 years old

Risk Factors

Increasing age
1. Odds Ratio increases 1.6 to 2.2 per decade of life
2. Prevalence at age 40-49 years old
  1. Black: 1.3 to 1.4%
  2. Hispanic: 0.5 to 1.3%
  3. Caucasian: 0.2 to 0.5%
3. Prevalence at age >80 years old
  1. Black: 11.3 to 23.2%
  2. Hispanic: 12.6 to 21.8%
  3. Caucasian: 1.9 to 11.4%
Ethnicity or Race
1. See age related Prevalence above
2. Black patients
  1. Relative Risk: 3.5 to 4 fold increase in Glaucoma risk over caucasian patients
3. Hispanic Patients
  1. Relative Risk: 2 fold increase in Glaucoma risk over caucasian patients
First Degree Relative with Glaucoma (4-16% Risk)
1. Sibling Relative Risk: 3.7 to 16
2. Child or parent Relative Risk: 1.1 to 2.2
3. Specific Glaucoma related genetic mutation accounts for <5% of cases
Diabetes Mellitus
1. Relative Risk: 1.4 to 1.5
Severe Myopia (Nearsightedness)
Eye Injury
1. Eye Trauma
2. Uveitis
3. Corticosteroids (especially intra- and periocular)

Pathophysiology

Increased Aqueous Humor production
Aqueous outflow obstruction by microscopic blockages
Normal chamber angles

Symptoms

Bilateral eyes affected but asymmetrically
Colored halos around lights
Asymptomatic until severe visual field or central loss
1. Visual field loss irreversible unless caught early
2. Compensation from opposite eye masks earlier visual changes
3. Insidious painless Vision Loss
  1. Peripheral Vision Loss progresses to blindness
  2. Loss not symptomatic until 40% of nerve fibers lost

Signs

Pupil dilatation
Increased Intraocular Pressure (by Tonometer)
1. IOP < 22 mmHg: Normal if optic disks normal
2. IOP 22-30 mmHg: Borderline
3. IOP >31 mmHg: Abnormal
Progressive peripheral Vision Loss
1. Stages of Vision Loss
  1. Stage 1: Loss of nasal and superior visual field
  2. Stage 2: Loss of peripheral visual field
  3. Stage 3: Total blindness
2. Screen visual fields by confrontation
3. Perimetry offers computerized visual field evaluation
Glaucomatous changes in the optic disc
1. General
  1. Focal thinning of neural rim
    1. Nerves at edge of cup and edge of disc
    2. Thinning seen at temporal (lateral) disc margin
  2. Superficial Hemorrhage overlying disc edge
2. Diagnostic changes
  1. Symmetrically enlarged cup-to-disc ratio >0.5 or
  2. Cup-to-disc ratio difference between eyes >0.2 or
  3. Significantly asymmetric cup in one eye

Diagnosis

Formal Open Angle Glaucoma diagnosis requires a combination of findings
1. IOP measurement
2. Stereoscopic Optic Nerve exam
3. Visual Field testing
Intraocular Pressure alone is not sufficient for diagnosis
1. Normal Intraocular Pressure in 50% of POAG
2. Most patients with Intraocular Pressure >22 mm Hg do not develop Glaucoma (with Optic Nerve injury)
3. Screening is not recommended to be performed in primary care (USPTF)
  1. Combination of factors needed for diagnosis (see signs above)
  2. Typically performed by eye specialists

Differential Diagnosis

Acute Angle Closure Glaucoma
1. Presents as a painful Red Eye
2. Requires immediate evaluation and management

Management

General
1. Regular aerobic Exercise reduces Intraocular Pressure
2. Emphasize Medication Compliance (<50% continue medications >1 year)
  1. Simplify regimens as much as possible
3. Approach treatment in similar fashion to systemic Hypertension Management
  1. Start with initial first-line agents
  2. Advance first-line agents
  3. Add additional medications as needed for persistent elevated pressures
First Line Agents
1. Prostaglandin Analogues (Latanoprost, Travoprost, Bimatoprost, Tafluprost, Unoprostone)
  1. Once daily, effective agent with low side effects
  2. Latanoprost (Xalatan) 0.005% one drop daily
2. Intraocular Beta Blockers (Betaxolol, Carteolol, Levobunolol, Metipranolol, Timolol)
  1. Less expensive than other Glaucoma medications
  2. Consider other medications if higher risk for adverse effects
    1. Systemic Beta Blocker use
    2. Beta Blockers otherwise contraindicated (e.g. COPD, Asthma)
  3. More adverse effects
    1. Due to Beta Blocker systemic absorption with Hypotension and bronchoconstriction risk
    2. See Don't Open Eyes Technique for Eye Drop Instillation (to reduce systemic absorption)
Second Line Agents
1. Intraocular Cholinergics (Pilocarpine, Carbachol)
Adjunctive Agents
1. Intraocular Sympathomimetic (Dipivefrin, Propine)
2. Topical Carbonic Anhydrase Inhibitor (Brinzolamide, Dorzolamide)
3. Intraocular Alpha-Adrenergic (Apraclonidine, Brimonidine)
Acute exacerbations of refractory chronic Glaucoma
1. Systemic Carbonic Anhydrase Inhibitor
Combination agents to consider
1. Dorzolamide and Timolol Maleate (Cosopt, generic)
2. Brinzolamide and Brimonidine (Simbrinza, expensive)
3. Brimonidine and Timolol (Combigen, expensive)
Surgery for refractory cases
1. Laser trabeculoplasty
  1. May be used as first line therapy (esp. for patients non-compliant with topical drops)
2. Surgical trabeculectomy
  1. Higher risk procedure used as last available option

Prevention

See Preventive Eye Examination for Glaucoma screening intervals

References