Glaucoma Primer for Expert Witness Testimony

posted in: Glaucoma

Glaucoma occurs when the pressure inside the eye becomes too high. Elevation of eye pressures causes damage to the optic nerve. A damaged optic nerve leads to visual loss. The goal in treating glaucoma has been to arrest the continuum that leads from its early stages when it does have symptoms to advanced disease where patients suffer from functional impairment. Glaucoma is the most common neurodegenerative disease.

When is pressure elevated?
Generally, a pressure that exceeds 21 mm Hg may predispose to glaucoma.

Can patients with normal eye pressure develop glaucoma?
A very small group of patients develop glaucoma despite eye pressures that would be considered normal. These patients have what is known as “normal-tension” glaucoma.

What tests are used to detect glaucoma?
1) Tonometry. This measures eye pressure.
2) Visual field testing also known as perimetry. This measures the field of vision.
3) Optic nerve photography
4) Optical Coherence Tomography (OCT). This measures the retinal nerve fiber layer and the structure of the optic nerve.

How is tonometry measured? A device known as a tonometer is gently applied to the eye following application of an anesthetic eye drop. The reading of the tonometer is a direct measurement of the eye pressure. Tonometry is non-invasive and complications from tonometry such as a corneal abrasion are extremely rare.

A visual field test measures the extent of straight-ahead (central) and side vision (peripheral vision). Glaucoma may present as loss of peripheral vision. The loss of peripheral vision may or may not have a specific pattern. Loss of peripheral vision in glaucoma usually occurs before loss of central vision.

Optic nerve photography is utilized to document the appearance of the optic nerve and serve as a baseline for future examinations.  A variety of structural changes of the optic nerve may indicate disease or progression of glaucoma.  The optic nerve is seen in color photographs as a disc with a white center.  The white center is known as the “cup” because it represents a crater within the surface of the optic nerve.  The ratio between the size of the cup and the overall size of the optic nerve is known as the cup to disc ration.  An enlarged cup happens when there is loss of optic nerve tissue from glaucoma.  Therefore the ratio of the cup to the overall size of the optic nerve (disc) is increased. A cup to disc ratio of 0.1 to 0.3 is considered within normal limits for most patients.  A ratio greater than 0.4 is suspicious for glaucoma.

Signs of glaucoma that may be visualized on optic nerve photos include splinter-like hemorrhages at the border of the optic nerve and notching of the optic nerve cup.  As glaucoma develops the optic nerve may appear white in appearance.  A chalky white appearance of the optic nerve is consistent with advanced glaucoma.

Optical coherence tomography measures the thickness of the retina nerve cells (ganglion cells). In glaucoma there is a progressive loss of ganglion cells from elevated eye pressure. The loss of ganglion cells in the retina often precedes loss of peripheral vision from months to years.

What factors predispose to glaucoma?
Besides elevated eye pressure, there are many other factors that may cause glaucoma. A family history of glaucoma, elevated blood pressure, and history of damage to the drainage pathway inside the eye can predispose to glaucoma.

What treatment is available for glaucoma?
Most patients use eye drops to reduce eye pressure. A laser procedure known as Selective Laser Trabeculoplasty (SLT) is also available. Surgical procedures known as filtering procedures are also available to reduce eye pressure.  Filtering procedures work by draining fluid from inside to outside of the eye.

What are the possible complications from glaucoma surgery?
• Eye infection
• Bleeding (hemorrhage)
• Abnormally high or low eye pressure
• Loss of vision
• Development of cataracts

What contribution may expert witness testimony provide?
A board certified ophthalmologist may be able to determine if the diagnosis and treatment are appropriate for a specific patient. Proper management and appropriate surgery, when indicated, are key aspects that are reviewed by a qualified glaucoma expert witness. An informed attorney may be able to determine if his client has the right to claim compensation when there is a breach in the standard of care.

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