Glaucoma (open-angle, closed-angle, and normal-tension) – pathology, diagnosis, treatment


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much more. Try it free today! Glaucoma is actually a group of 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. 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 in the anterior section of the eye, while the vitreous
chamber is part of the posterior section of the eye. Typically all of the chambers in the eye are
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, watery
fluid that is 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 Schlemm and finally
into aqueous veins that are part of the episcleral venous system—the veins around the sclera
of the eye. 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 pressure greater than 21 mmHg or 2.8kPa. The high pressure affects all of the structures
in 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’re a couple types of glaucoma,
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, so there’s a 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 glaucoma, also called angle-closure
glaucoma or narrow-angle glaucoma, and this is due to the angle between the iris of 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 up against the iris. The result is that the drainage system gets
blocked again, but this time causes a rapid buildup of pressure within the eye, causing
an abrupt onset of severe eye pain, eye redness, blurry vision, headaches, nausea, and visual
haloes. 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. 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, that 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. While 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 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 treat closed angle glaucoma. And there are also laser treatments, for example
ones that destroy the humor-producing cells, which reduces 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. Alright 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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