Glaucoma

Glaucoma is an assortment of eye diseases, which in most cases, are characterized by elevated intraocular pressure (IOP). This elevated pressure is caused by a buildup of fluid (aqueous humor) in the eye. Over time, this pressure causes damage to the optic nerve, resulting in loss of peripheral vision.

Elevated IOP is normally any IOP above 20mmhg.

IOP is not static. It changes throughout the day, usually being highest in the morning and gradually decreasing as the day progresses.

Elevated IOP is different from elevated blood pressure. Blood pressure can be affected by mood, diet, exercise levels, etc.

Elevated IOP is strictly a “plumbing issue”. Think of your eye as a sink, in which the faucet is always running and the drain is always open.

Your eye produces aqueous humor at a constant rate. This fluid also flows out of the eye at a constant rate, thru a drain called the trabecular meshwork. As the drain becomes clogged, the fluid begins to build up, causing the eye to become pressurized, like an overfilled balloon.

As pressure increases, it pushes against the optic nerve, which is the weakest part of the eye. Over time, this constant pressure causes damage to the optic nerve, resulting in a loss of peripheral vision. The loss of peripheral vision manifests itself as a “tunneling” of your vision.

Glaucoma is known as the silent robber of sight since there are no symptoms associated with the disease.

Early diagnosis and treatment is critical in preventing optic nerve damage and maintaining vision.

Glaucoma can be diagnosed through a painless comprehensive exam by your ophthalmologist.

Current diagnostic tests available at Terry & Alsheikh Eye Associates include:

Visual Field Test/Perimetry – A test that maps a person’s field of vision, in order to detect any defects. The test is done with one eye patched. The head and forehead are held flush against a chin and forehead rest. The eye that is being tested is looking straight ahead at a fixation light. During the test, a series of lights will flash on and off at different places on a white domed surface. The lights will be different sizes and different intensities, and you will be asked to press a button every time you see a light in order to record your response.

Since glaucoma tunnels your vision, this test is able to pick up finite changes in your visual field. In many cases, the test is able to pick up changes before the individual is even aware that a change has taken place.

There are 3 main types of visual fields:

  • Humphrey Visual Field (HVF) – Computerized perimetry that stimulates parvocellular ganglion cells in primary visual cortex.
  • Frequency Doubling Technology (FDT) – Computerized perimetry that stimulates magnocellular ganglion cells in primary visual cortex. This test can detect very early glaucomatous damage. This test can only be done in patients with good visual acuities.
  • Goldmann Visual Field (GVF)-manual perimetry used in patients with poor visual acuity, or in patients with slower reflexes.

 

Tonometry – A test that measures intraocular pressure, or the pressure inside the eye. The measurement usually involves anesthetizing the cornea with a numbing drop, then lightly touching the surface of the cornea with a probe to obtain a measurement in mmHg.

Corneal Pachymetry – A test that measures the thickness of the cornea. The measurement is an important diagnostic tool that an ophthalmologist uses to gauge the severity of a patient’s glaucoma, or their likelihood of developing glaucoma. People who have ocular hypertension (OHT) and thin corneas are at greater risk of developing glaucoma than people with OHT and normal to thick corneas. In addition, glaucoma patients with thin corneas are more likely to become worse over time, than glaucoma patients with normal to thick corneas.

Gonioscopy – A quick and painless examination of the angle that is formed when the iris meets the cornea, for the purpose of diagnosing open and narrow angle glaucoma. This exam is completed by placing a goniolens on the surface of the cornea, and examining the angle under magnification.

Ocular coherence tomography (OCT) – An advanced imaging technology, similar to an ultrasound, that uses light instead of sound, to obtain 2 and 3d cross sectional images of the retina and optic nerve. In glaucoma management, these cross-sectional images measure the thickness of the retinal nerve fiber layer (RNFL). As glaucoma progresses, the RNFL becomes thinner. By consistently taking RNFL measurements, an ophthalmologist can track your progress and detect very early glaucomatous damage to the optic nerve. If any changes are noted, treatment can be adjusted accordingly, thus preventing any loss of vision associated with glaucoma.

Glaucoma is thought to be hereditary.

Risk factors for developing glaucoma include:

  • A family history of glaucoma
  • Being aged 50 or over
  • African American or Hispanic descent
  • Having diabetes or cardiovascular disease
  • Being very near-sighted /myopic

Glaucoma can be roughly categorized as open angle or narrow angle glaucoma.

Primary Open Angle Glaucoma (POAG) – The term angle refers to the space between the cornea and the iris. Where the cornea and iris meet, an angle is formed, and at the base of that angle is where the trabecular meshwork is located. If the angle is open, the fluid can reach the drain and leave the eye.

Open angle glaucoma refers to a condition where the angle is open, but the IOP is still elevated due to a clogged drain. Thus, the fluid can reach the drain, but can’t exit the eye, causing a build up of excess fluid, and subsequent high IOP.

Current treatments for open angle glaucoma include:

New treatments for open angle glaucoma:

Narrow Angle Glaucoma refers to the anterior chamber depth being too small. The angle where the cornea and iris meet is too shallow, making the trabecular meshwork hard to reach, thus the fluid can’t readily drain from the eye.

Narrow angle glaucoma refers to a condition where the drain is fully functional, but fluid still accumulates, and IOP becomes elevated, because it can’t fully access the drain.

If the angle completely closes (acute angle closure), the drain becomes inaccessible, causing a dramatic increase in IOP, and possible total vision loss within 12 to 24 hours if immediate treatment is not received.

Current treatments for narrow angle glaucoma include:

Open angle glaucoma suspect/ocular hypertension (OHT) is a condition usually characterized by elevated IOP’s, but upon examination, gonioscopy, visual fields, and RNFL analysis, all yield results that are within normal limits (WNL). Patients can also present with other risk factors for developing POAG such as ABNL optic discs, a family history of glaucoma, or being of African American or Hispanic descent. These risk factors, with a combination of test results, which are WNL, will result in a classification as an open angle glaucoma suspect.

Glaucoma syndromes

Pigment dispersion syndrome (PDS) is a rare condition characterized by the iris rubbing up against the natural lens of the eye, causing iris pigment granules to flake off into the aqueous humor. Once this occurs, the iris granules can become trapped in the trabecular meshwork, where they can continue to build up, and eventually clog the drain of the eye. As the drain becomes clogged, the IOP becomes elevated, eventually leading to the development of pigmentary glaucoma.

A higher incidence of PDS has been seen in young Caucasian men between 20 and 40 years of age.

High myopia is also believed to be a risk factor for development of PDS.

Exercise can increase the amount of pigment granules flaking off from the iris, thus vigorous exercise should be avoided.

Patients that develop pigmentary glaucoma should be treated aggressively due to the rapid progression of the disease.

Treatment for PDS:

Patients with PDS can either be closely monitored (4 times per year) without treatment, or can be treated with miotic eye drops, such as Pilocarpine. Treatment with Pilocarpine has a dual effect. It not only lowers IOP, but by constricting the pupil, it also increases the space between the peripheral iris and the zonular fibers of the lens, thus decreasing the amount of pigment granules that flake off.

Laser surgeries such as SLT and ALT, which attempt to unclog the drain, can also be performed. see glaucoma surgery and laser link

Pseudoexfoliation syndrome (PXS) is a common systemic disease characterized by the production, shedding, and accumulation of a fibrillar protein. This disease affects the eye and internal organs. It has been associated with cardiac and cerebrovascular diseases (a group of diseases that affect the blood flow to and from the brain), such as coronary artery disease, aortic aneurysm, and peripheral artery disease.

These fibrils are produced by the cornea, iris, and lens of the eye. Eventually, the protein fibrils are shed and begin to float in the aqueous humor. As the aqueous humor begins to drain from the eye, the fibrils begin to accumulate in the trabecular meshwork, resulting in a clogging of the drain. As the drain progressively clogs, aqueous humor builds up in the eye, and leads to an increase in IOP.

PXS can lead to the development of pseudoexfoliation glaucoma.

PXS is rarely seen in people less than 40 years of age, and is more prevalent in people 70 or older.

PXS is a common systemic disease found in populations around the world.

A clinical examination of the eye with a microscope (slit lamp) yields the presence of “dandruff-like” flakes that have accumulated on the surface of the lens.

PXS is linked to specific complications during cataract surgery.

PXS is thought to be hereditary. Current research shows a strong genetic link involving single nucleotide polymorphisms (SNP’s) of the loxl1 gene.

Treatment for PXS

Congenital glaucoma

Low tension glaucoma

Other Glaucomas

Steroid induced glaucoma

Neovascular glaucoma

Glaucoma Surgery
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