Glaucoma

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Introduction0:00–0:15

[Osmosis sound logo] Glaucoma is actually a group of eye diseases that are usually due to intraocular hypertension --or increased pressure in the eye-- which damages the optic nerve and, if left untreated, can lead to blindness.

Physiology0:15–1:43

Taking a closer look at this cross-section of the eye, you can see that it's split up into different chambers. The anterior chamber includes the area from the cornea to the iris; the posterior chamber is this really narrow space between the iris and the lens; and then this larger, vitreous chamber includes the space between the lens and the back of the eye.
Not to be too confusing, but both the anterior and posterior chambers are located within the anterior section of the eye, while the vitreous chamber is part of the posterior section of the eye.
Typically, each of these chambers is filled with fluid. The chambers in the anterior section are filled with a liquid called aqueous humor and the posterior section is filled with vitreous humor.
The aqueous humor is a transparent and watery fluid that's secreted by the ciliary epithelium, which, in addition to secreting aqueous humor and providing nutrients to the lens and cornea, it provides structural support and helps to keep the shape of the eye.
So that fluid's secreted into the posterior chamber, and then flows through a narrow space between the front of the lens and the back of the iris, through the pupil, to the anterior chamber.
From there, the fluid flows out of the eye through the trabecular meshwork, which is a spongy tissue that acts like a drain, and this allows the fluid to go down into a circular channel called the canal of Schelmm, and finally into the aqueous veins, which are part of the episcleral venous system --the veins around the sclera of the eye.

Pathology1:43–2:21

In glaucoma, part of this aqueous humor drainage pathway becomes partially or completely blocked, so that fluid can't easily drain out.
This causes the pressure within the fixed space of the anterior chamber to quickly build up, causing intraocular hypertension, which is defined as a pressure greater than 21 millimeters of mercury or 2.8 kiloPascals.
This high pressure affects all the structures of the eye, including the optic nerve, which is the nerve that carries visual information from the eyes to the brain.
And this means that, over time, as the optic nerve gets damaged, glaucoma leads to vision loss. Now, there are a couple of types of glaucoma.

Open angle glaucoma2:21–2:58

First, there's open-angle glaucoma, which is actually the most common, and it has this name because the angle between the cornea and the iris is "open".
In this type, the drainage system slowly gets clogged over time, and so, there's this gradual increase in pressure on the optic nerve.
This increase in pressure initially results in atrophy of the outer rim of the nerve, resulting in a decrease in peripheral vision.
As that pressure increases even more though, there's continued damage to the optic nerve, which eventually leads to a loss in central vision, as well.

Closed angle glaucoma2:58–3:34

Another type of glaucoma is closed-angle glaucoma, also known as angle-closure glaucoma or narrow-angle glaucoma, and this is due to the angle between the iris and the cornea being too small, meaning that the passageway for aqueous humor outflow is too narrow and this is as a result of the lens being pushed against the iris.
The result of this is that the drainage system gets blocked again, but this time causes a rapid buildup of pressure within the eye, which can cause abrupt onset of: severe eye pain, eye redness, blurry vision, headaches, nausea, and visual haloes.

Normal or low tension glaucoma3:34–3:57

Finally, normal-tension glaucoma --or low-tension glaucoma-- happens when the pressure's normal in the eye. The cause of normal-tension glaucoma is largely unknown, although it's thought that the optic nerve becomes damaged due to hypoperfusion --or poor blood flow-- as well as, potentially, genetic hypersensitivity to pressures that are "even" in the normal range.

Diagnosis3:57–4:25

For diagnosis of glaucoma, tonometry can be used to assess for increased intraocular pressure. Also though, visual field testing can be done, as well as looking for optic nerve damage --either through imaging or by direct observation.
In particular, the pressure on the optic nerve results in a thinning of the outer rim of the nerve, which starts to give it this cup shape-- and this is called "cupping"--and it's often seen in individuals with glaucoma.

Treatment4:25–5:48

Even though glaucoma is not curable, it can be slowed with treatment. If the underlying issue is intraocular hypertension, then it can be managed by taking medications that decrease the pressure in the eye.
This can be done in a couple of ways: First, by decreasing the production of aqueous humor --with medications like beta-adrenergic receptor antagonists and carbonic anhydrase inhibitors.
Also though, you can increase the outflow of aqueous humor --by taking prostaglandin analogs. Or finally, some medications both decrease production and increase outflow --like alpha adrenergic agonists.
In addition to medications, there are also laser treatments available. For example: trabeculoplasty is a treatment where a laser is used to open the trabecular mesh network and this helps treat open-angle glaucoma.
And there's also iridotomy, which uses a laser to punch a tiny hole in the iris --which helps to treat closed-angle glaucoma.
And there are also other laser treatments: For example, ones that destroy the humor-producing cells --which reduces the production of the fluid; and in serious cases, --sometimes they can be used to create a new channel through which the aqueous humor can be drained out.
And, finally, there are implants that shunt fluid out of the anterior chamber by bypassing the trabecular meshwork and collecting system.

Review5:48–6:13

All right, as a quick recap: Glaucoma is an eye disease where a buildup of aqueous humor causes increased pressure in the eye and this damages the optic nerve and can result in blindness.
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