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
Ocular predisposition
1. Severe Myopia (Nearsightedness)
2. Thin central Cornea
Eye Injury
1. Eye Trauma
2. Uveitis
3. Corticosteroids (especially intra- and periocular)

Associated Conditions

Endocrine
1. Diabetes Mellitus
  1. Glaucoma Relative Risk: 1.4 to 1.5
2. Hypothyroidism
3. Cushing Disease
Cardiopulmonary
1. Obstructive Sleep Apnea
2. Cardiovascular Disease
Hematologic
1. Sickle Cell Disease
Inflammatory and Infectious conditions
1. Herpetic infections
2. Lyme Disease
3. Rheumatoid Arthritis
4. Sarcoidosis
5. Systemic Lupus Erythematosus
Miscellaneous
1. Aggressive Blood Pressure lowering

Pathophysiology

Increased Aqueous Humor production
Aqueous outflow obstruction by microscopic blockages
Normal chamber angles (contrast with Narrow Angle Glaucoma)
Increased introcular pressure progressively compresses the Optic Nerve Heads and injures the Retinal axons
1. Vascular theory suggests an ischemic injury mechanism
2. Neurodegenerative theory suggests Autoimmunity or failed nerve repair mechanisms

Symptoms

Bilateral eyes affected but asymmetrically
Colored halos around lights
Reduced contrast sensitivity
1. Decreased ability to distinguish small objects against their background
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. Gradual blind spot development
  2. Peripheral Vision Loss progresses to blindness
  3. 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. Visual Field changes do not occur until 50% of Retinal pigment cells are lost
2. 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
3. Methods
  1. Screen Visual Fields by confrontation
  2. Perimetry
    1. Computerized Visual Field evaluation
Glaucoma-Related changes in the optic disc
1. General
  1. Optic Cup becomes more prominent (cupping) as the Neuroretinal Rim thins
  2. Focal thinning of Neuroretinal Rim
    1. Nerves at edge of cup and edge of disc
    2. Thinning may be most prominent at temporal (lateral) disc margin
    3. Thinning may be asymmetric with "notching" at regions of thinning
  3. Superficial Hemorrhage overlying disc edge
2. Diagnostic changes
  1. Symmetrically enlarged cup-to-disc ratio >0.3 to 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. Optic disc changes and Visual Field Deficits may be present without IOP increase on initial presentation
2. Normal Intraocular Pressure in 40-50% of POAG at time of diagnosis
  1. A single value may be insufficient to exclude Ocular Hypertension (IOP is lower in the evening)
3. Most patients with Intraocular Pressure >21 mm Hg do not develop Glaucoma (with Optic Nerve injury)
  1. Elevated Intraocular Pressure results in Glaucoma in 10% at 5 years and 30% at 20 years
4. 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
Other testing performed by Ophthalmology
1. Pachymetry (Corneal thickness measurement)
2. Gonioscopy (anterior chamber angle)
3. Optical Coherance Tomography (OCT)
  1. Evaluates Optic Nerve Head anatomy by analyzing reflected light off the optic disc
  2. Neuroretinal Rim thinning identified on serial OCT evaluations often precedes Visual Field Deficits

Differential Diagnosis

Acute Angle Closure Glaucoma
1. Presents as a painful Red Eye
2. Requires immediate evaluation and management
Optic Neuropathy
1. Ischemic Optic Neuritis
2. Retrobulbar Optic Neuropathy (Multiple Sclerosis)

Management

Precautions
1. Diagnosis of Glaucoma is often unclear early in the course
2. Serial, longterm periodic Eye Exams by ophthalmology are required
Decision for ophthalmologists to start medications is based on multiple factors
1. Optic Nerve and optic disc status
2. Normal Intraocular Pressure may still warrant medication management to lower IOP
  1. Glaucoma related changes (e.g. Optic Cupping, peripheral field deficit) should be treated
  2. Rate of IOP increase may indicate starting medications more than the absolute IOP measurement
3. Ocular Hypertension associated risk of Glaucoma
  1. https://ohts.wustl.edu/risk/
  2. Increased Intraocular Pressure alone is not always an indication to start medications
General
1. Regular aerobic Exercise reduces Intraocular Pressure
2. Emphasize Medication Compliance (<50% continue medications >1 year)
  1. Simplify regimens as much as possible
  2. Review barriers with patients (e.g. cost, adverse effects)
  3. Consider generic, inexpensive alternative medications for patients for whom cost is a barrier
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. Increases uveoscleral aqueous outflow (lowers IOP 25 to 35%)
  2. Once daily, effective agent with low side effects
  3. Latanoprost (Xalatan) 0.005% one drop daily
2. Intraocular Beta Blockers (Betaxolol, Carteolol, Levobunolol, Metipranolol, Timolol)
  1. Decrease Aqueous Humor production (lowers IOP 20-25%)
  2. Less expensive than other Glaucoma medications
  3. Consider other medications if higher risk for adverse effects
    1. Systemic Beta Blocker use
    2. Beta Blockers otherwise contraindicated (e.g. COPD, Asthma)
  4. 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)
  1. Increase aqueous outflow (lowers IOP 20 to 30%)
Adjunctive Agents
1. Intraocular Sympathomimetic (Dipivefrin, Propine)
2. Topical Carbonic Anhydrase Inhibitor (Brinzolamide, Dorzolamide)
  1. Decrease aqueous production (lowers IOP 15-20%)
3. Intraocular Alpha-Adrenergic (Apraclonidine, Brimonidine)
  1. Decrease aqueous production and increase aqueous outflow (lowers IOP 20 to 25%)
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)
New novel medications
1. Latanoprostene (Vyzulta)
2. Netarsudil (Rhopressa)
  1. Rho-Kinase Inhibitor lowers Episcleral venous pressures and increases aqueous outflow (lowers IOP 10 to 20%)
Surgery for refractory cases
1. Selective Laser trabeculoplasty (SLT)
  1. Increases permeability of the trabecular meshwork, reducing resistance to aqueous outflow to venous system
  2. May be used as first line therapy (esp. for patients non-compliant with topical drops)
  3. When compared with Topical Medications, SLT had better outcomes, and 75% no longer needed Topical Medications
  4. Gazzard (2019) Lancet 393(10180): 1505-16 [PubMed]
2. Surgical trabeculectomy
  1. Small incision made in Sclera to increase aqueous fluid drainage
  2. Higher risk procedure used as last available option

Prevention

See Preventive Eye Examination for Glaucoma screening intervals
Glaucoma Screening Indications
1. USPTF does not recommend routine screening for Glaucoma in the general adult population
2. U.S. Centers for Medicare and Medicaid (CMS) covers eye care professional exams for high risk conditions
  1. Diabetes Mellitus
  2. Family History of Glaucoma
  3. African Descent (age over 50 years)
  4. Hispanic Descent (age over 64 years)
3. Eyecare America (AAO sponsored)
  1. https://www.aao.org/eyecare-america
  2. No cost Glaucoma exams and follow-up for patients at moderate to high risk for developing Glaucoma

Complications

Blindness
1. Without treatment, POAG progresses from normal Vision to blindness over 25 years
2. More than half of patients are asymptomatic, as peripheral Vision Loss goes unnoticed until severe

References