eMedicine Specialties > Ophthalmology > Intraocular Pressure

Glaucoma, Low Tension: Differential Diagnoses & Workup

Author: Iqbal Ike K Ahmed, MD, FRCSC, Clinical Assistant Professor, Department of Ophthalmology, University of Utah
Coauthor(s): Baseer U Khan, MD, Staff Physician, Department of Ophthalmology, University of Toronto, Canada; Khalid Hasanee, MD, Glaucoma and Anterior Segment Fellow, Department of Ophthalmology, University of Toronto
Contributor Information and Disclosures

Updated: Jun 22, 2006

Differential Diagnoses

Other Problems to Be Considered

Intermittent IOP elevation
Burned-out glaucoma
Nonglaucomatous optic nerve
Congenital disc anomalies/cupping
Myopia with peripapillary atrophy
Optic nerve coloboma/pit
Vascular etiology
Carotid and ophthalmic artery occlusion
Previous blood loss or shocklike episode
Neurologic etiology
Hereditary optic neuropathy
Leber optic atrophy
Dominant or recessive optic atrophy
Tonometric error (thin cornea)

Workup

Laboratory Studies

• Perform blood tests
  • CBC (rule out anemia)
  • Erythrocyte sedimentation rate (ESR) rarely is elevated in LTG and typically is obtained in cases of decreased central acuity with a pale nerve to rule out anterior ischemic optic neuropathy (AION).
  • Rapid plasma reagent (RPR), fluorescein treponema antibody (FTA)
  • Checking for the presence of antinuclear antibody (ANA) is recommended to rule out collagen-vascular and autoimmune diseases. Screening for extractable nuclear antigens (ie, Ro, La, Sm) also is recommended to rule out autoimmune diseases.
  • Serum immunofixation for monoclonal gammopathy is indicated. Approximately 10% of patients with LTG have monoclonal gammopathy (paraproteinemia), which represents a benign condition two thirds of the time. However, lymphoproliferative disorders (ie, cancers) need to be ruled out by a hemato-oncology specialist if this test is positive.
  • High-sensitivity C reactive protein is becoming the criterion standard for documenting both symptomatic and nonsymptomatic ischemic heart disease and is often positive in patients with LTG.
  • Mitochondrial testing for Leber (when indicated)

Imaging Studies

• Optic nerve head and/or retinal nerve fiber analysis may be helpful in diagnosing and monitoring progression of glaucomatous optic neuropathy.
  • Analyze optic nerve head with confocal scanning laser ophthalmoscopy (SLO), eg, Heidelberg Retinal Tomograph, or optical coherence topography (OCT).
  • Analyze retinal nerve fiber with confocal SLO, OCT, or scanning laser polarimetry (GDx). Often, retinal nerve fiber layer changes may occur before any changes on visual field testing. Most often nerve fiber layer thinning occurs first in the superior and inferior poles.
• Neuroimaging of orbits and head
  • MRI is the preferred imaging modality compared to CT scan because of its higher sensitivity.
  • Controversy exists as to whether neuroimaging should be performed routinely. Some advocate referral to neuroophthalmology if concerned.
  • Neuroimaging should be performed in any case with the following:
    • Markedly asymmetric disease
    • Increased optic disc pallor relative to cupping
    • Unusual visual field defects, particularly those with respect to the vertical midline
    • Rapid progression of visual fields
    • Rapid progression of optic neuropathies
    • Dyschromatopsia
    • Afferent papillary defect with mild cupping
• If indicated, carotid Dopplers are recommended to rule out carotid insufficiency.
• When indicated, a chest x-ray is necessary to rule out sarcoidosis.

Other Tests

• To rule out nocturnal hypotension, 24-hour ambulatory blood pressure monitoring is advised.
• Diurnal tension curve: Although IOP may be normal during an examination, the patient may have intermittent spikes in IOP throughout the day that may explain optic nerve and visual field damage.
• Future diagnostic modalities - Ocular blood flow analysis
  • SLO - Retinal and choroidal, superficial optic nerve head
  • Doppler ultrasound - Carotid arteries
  • Confocal scanning laser Doppler flowmetry (Heidelberg Retinal Flowmetry) - Short PCA circulation, optic nerve head

Histologic Findings

Findings include posterior deformation of cribriform plate, with compression of lamina due to direct deformation by secondary vascular compression, resulting in glial atrophy.

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