Target Health Blog

Glaucoma

January 14, 2019

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Quiz
Source:

Photo showing conjunctival vessels dilated at the corneal edge (ciliary flush, circumcorneal flush) and hazy cornea characteristic of acute angle closure glaucoma Photo credit: By Jonathan Trobe, M.D. - The Eyes Have It, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=16116086

According to National Eye Institute projections, by the year 2020, 80 million people worldwide will have glaucoma, with about 2 million people in the United States being affected. The risk of vision loss due to glaucoma increases sevenfold after the age of 55.

The word “glaucoma“ comes from the Ancient Greek a derivative of which commonly described the color of eyes which were not dark (i.e. blue, green, light gray). Eyes described as glaucomic due to disease might have had a gray cataract in the Hippocratic era, or, in the early Common Era, the greenish pupillary hue sometimes seen in angle-closure glaucoma.

Glaucoma is a group of 1) ___ diseases which result in damage to the optic nerve and vision loss. The damage begins in the peripheral visual field and progresses toward the center, resulting in complete blindness unless detected early. For this reason, degeneration in glaucoma is often hard to detect. The most common type is open-angle glaucoma with less common types including closed-angle glaucoma and normal-tension glaucoma. Open-angle glaucoma develops slowly over time and there is no pain. Closed-angle glaucoma can present gradually or suddenly. The sudden presentation may involve severe eye pain, blurred vision, mid-dilated pupil, redness of the eye, and nausea. Vision loss from glaucoma, once it has occurred, is permanent.

Risk factors for glaucoma include increased 2) ___ in the eye, a family history of the condition, and high blood pressure. For intraocular pressure (IOP), a value of greater than 21 mmHg or 2.8 kPa is often associated to a greater risk of developing glaucoma. However, some may have high eye pressure for years and never develop damage. Conversely, optic nerve damage may occur with normal pressure, known as normal-tension glaucoma. The mechanism of open-angle glaucoma is believed to be slow exit of aqueous humor through the trabecular meshwork while in closed-angle glaucoma the iris blocks the trabecular meshwork. Diagnosis is by a dilated eye examination. Often the optic nerve shows an abnormal amount of cupping.

If treated early it is possible to slow or stop the progression of disease with medication, laser treatment, or surgery. The goal of these treatments is to decrease eye pressure. A number of different classes of glaucoma medication are available. Laser treatments may be effective in both open-angle and closed-angle glaucoma. A number of types of glaucoma surgeries may be used in people who do not respond sufficiently to other measures. Treatment of closed-angle glaucoma is a medical emergency.

Glaucoma occurs more commonly among 3) ___ people. Closed-angle glaucoma is more common in women. Glaucoma has been called the “silent thief of sight“ because the loss of vision usually occurs slowly over a long period of time. Worldwide, glaucoma is the second-leading cause of blindness after cataracts. While the word glaucoma is of Greek origin, in English, the word was used as early as 1587. However, it did not become commonly used until after 1850, when the development of the ophthalmoscope allowed people to see the optic 4) ___ damage.

The modern goals of glaucoma management are to avoid glaucomatous damage and nerve 5) ___, and preserve visual field and total quality of life for patients, with minimal side-effects. This requires appropriate diagnostic techniques and follow-up examinations, and judicious selection of treatments for the individual patient. Although IOP is only one of the major risk factors for glaucoma, lowering it via various pharmaceuticals and/or surgical techniques is currently the mainstay of glaucoma treatment. A review of people with primary open-angle glaucoma and ocular hypertension concluded that medical IOP lowering treatment slowed down the progression of visual field loss.

Vascular flow and neurodegenerative theories of glaucomatous optic neuropathy have prompted studies on various neuroprotective therapeutic strategies, including nutritional compounds, some of which may be regarded by clinicians as safe for use now, while others are on trial. Intraocular pressure can be lowered with medication, usually eye 6) ___. Several classes of medications are used to treat glaucoma, with several medications in each class. Each of these medicines may have local and systemic side effects. Adherence to medication protocol can be confusing and expensive. If side effects occur, the patient must be willing either to tolerate them or to communicate with the treating physician to improve the drug regimen. Initially, glaucoma drops may reasonably be started in either one or in both eyes. Wiping the eye with an absorbent pad after the administration of eye drops may result in fewer adverse effects, like the growth of eyelashes and hyperpigmentation in the eyelid. Poor compliance with medications and follow-up visits is a major reason for vision 7) ___. A recent study of patients in an HMO found half failed to fill their prescriptions the first time, and one-fourth failed to refill their prescriptions a second time. Patient education and communication must be ongoing to sustain successful treatment plans for this lifelong disease with no early symptoms.

A recent study published in the Proceedings of the National Academy of Sciences, describes recent experiments showing that glaucoma is very much like other central nervous system diseases. This is a paradigm shift on how we think about this disease and will have global implications. This information opens up an entirely new domain of nerve-derived therapeutics. Combining this new understanding of where the first neuronal injury for glaucoma occurs, with the fact that the incidence of injury increases with age, researchers now have insight into how the loss of sensory function occurs in normal aging. Traditionally, glaucoma therapies have focused on lowering ocular pressure within the eye. But this new study gives credence to taking a new direction by focusing on neuronal activity in the middle of the 8) ___, where the optic nerve forms its first connections. This work demonstrates that we must consider both the eye and the brain when trying to understand blinding diseases such as glaucoma. The neurobiological approach will lead to new targets for potential treatments.

In other age-related diseases, like Alzheimer's disease and Parkinson's disease, the most significant contributor to neuronal susceptibility to injury is age. In these diseases, the injury to neurons occurs very early in the distal projections in a process called dying back. In dying back, the neuronal axon loses its ability to communicate with the target. In the case of glaucoma, it has been shown that the axons in the 9) ___ nerve lose their ability to communicate with their projection site in the mid-brain. The authors expected to find a loss of communication in the optic nerve of the eye, but what they also discovered was that the connectivity between the optic nerve and the brain was dying first. Using animal models with high pressure glaucoma, the authors were able to see that a very early mechanism of vision loss involves the breakdown of communication between the optic nerve and the mid-brain, where sensory information about sound, heat, cold, pain and pressure originate. By following the disease long enough, eventually the optic nerve, then the retina, showed signs of degeneration. Interestingly, the degeneration works in reverse order. It starts in the brain and works its way back to the retina so that in the very latest stages of the disease, the earliest structures, the ones nearest the eye, are the last to go.

Presently, the authors are exploring drugs that can improve or restore the connectivity between the optic nerve and the mid-brain. Using both synthetic compounds and natural nerve growth factors such as brain-derived neurotrophic factor (BDNF), the team is examining how to restore communication in the pathway. The study, also introduces the possibility of using MRI scans as an early 10) ___ tool.

Sources: Vanderbilt University Medical Center; David Calkins, Ph.D; Sam Crish PhD; nih.gov; Glaucoma Research Foundation; National Eye Institute; Research to Prevent Blindness; Wikipedia

ANSWERS: 1) eye; 2) pressure; 3) older; 4) nerve; 5) damage; 6) drops; 7) loss; 8) brain; 9) optic; 10) diagnostic

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