Why is this topic important;
Glaucoma is the second-leading cause of blindness in the world, affecting around 70 million people globally.
Glaucoma is a group of diseases affecting the eyes. In lay terms, I can describe this disease as a pot placed on a tripod stand. The tripod stand here is the 3 sequences of events that give rise to glaucoma which are; 1. There is abnormally high pressure in the eye (raised intraocular pressure). 2. This pressure leads to the damage of the nerve which relates information between the eye and the brain (Optic nerve damage) and 3. This optic nerve damage results in loss of vision.
By National Eye Institute, Public Domain, Wikimedia
So, first of all, let us look at how this raised intraocular pressure occurs.
The eye produces a fluid called the aqueous humor. This fluid is produced by a part of the eye called the ciliary body. The fluid helps to provide nutrients to the eyes, especially the cornea and the lens since they don't have any blood vessels to supply nutrients to them. It also removes waste products from the eyes and maintains the pressure in the eyes.
When the fluid is produced, it flows from the posterior chamber of the eye, through the pupil, to the anterior chamber of the eye, and after performing its functions, it drains through some structures in the eye which are the trabecular meshwork, canal of shlemn and then to the aqueous veins. There is also the uveoscleral outflow channel. These maintain the pressure in the eye at a normal range of 10 - 21 mmHg.
This sequence of production, flow, and drainage is always tightly regulated to maintain a specific quantity of this fluid in the eyes at all times. Anything that will cause the eye to produce this fluid more than it is drained, or not to drain as much as that is produced, will lead to the accumulation of this fluid in the eyes which will cause a rise in the pressure within the eye (intraocular pressure). This raised intraocular pressure through mechanical, vascular, and other mechanisms cause damage to the optic nerve by killing the retinal ganglion cells. This optic nerve damage is irreversible.
Having understood how the raised eye pressure and nerve damage occurs, let us discuss how this leads to loss of vision.
The optic nerve is the 2nd cranial nerve and its function is to transmit visual information (impulses) from the eyes to the brain. The brain then interprets the information and sends feedback to the eye and vision occurs. When light from an object enters the eyes, it passes through the lens and falls on the retina which has the photoreceptors (the rods and the cons). This sends the impulse to the optic nerves which transmit it to the brain through the visual pathway. Therefore, the optic nerve plays a very key role in vision and any damage to it invariably leads to loss of vision as seen in glaucoma. This vision loss follows a specific pattern and usually, peripheral (side) vision is lost before the central vision.
By Myupchar, CC BY-SA 4.0, Wikimedia
TYPES OF GLAUCOMA
Glaucoma can be grouped into 3; congenital glaucoma, primary glaucoma, and secondary glaucoma. We will look at them one after another, their differences, and their treatment options.
In congenital or developmental glaucoma, there is a problem in the development of the eye, the angle structure of the eye where the drainage apparatus for the aqueous humor is located is not well developed.
So glaucoma can manifest at any point in childhood and this can be further grouped into 3 depending on the age at which glaucoma manifests.
The first group is the true congenital glaucoma where the baby develops a raised intraocular pressure from the womb and by the time the child is born, from the first day of life, the child already has glaucoma. The second group is infantile glaucoma where the disease manifests before the child is 3 years of age. And the last group is juvenile glaucoma where the disease manifests between the age of 3 to 16 years. Though these conditions are relatively rare, it is always a big concern for parents to see their child develop glaucoma at that early age.
How to notice this is that the child's eyeball becomes enlarged, with increased sensitivity to light (photophobia), excessive blinking of the eyes (blepharospasm), and tearing of the eyes (lacrimation).
For these patients, surgery is always the preferred choice of treatment. However, drugs like Timolol can be used while making plans for surgery. The surgical option of choice is goniotomy where the surgeon makes an opening in the trabecular meshwork to allow the drainage of the aqueous humor. The second available surgical option is trabeculoplasty which also helps to drain the aqueous humor and reduce the intraocular pressure. There is a need for proper monitoring and follow-up after the surgery.
By National Eye Institute, National Institutes of Health, Public Domain, Wikimedia
The second type of glaucoma is primary glaucoma in which there is no known identifiable cause. This second type is further grouped into 2, which are the Primary Open Angle Glaucoma and the Primary Angle Closure Glaucoma.
In the primary open-angle glaucoma, there is a blockage of the trabecular meshwork which impairs the drainage of the aqueous humor. However, the second drainage channel, uveoscleral outflow is still open. So the increase in intraocular pressure builds on gradually and can occur without any symptoms. This is why this type of glaucoma is dangerous. It can go on unnoticed till the optic nerve is totally damaged.
Some of the symptoms that the patient may notice include, mild headache, eye pain, blurring of vision, seeing color haloes around lights, etc. Sometimes, this type of glaucoma is detected incidentally during a regular eye check-up. The primary open-angle glaucoma is the commonest type of glaucoma.
The risk factors include age above 40 years, family history of glaucoma, race, some health conditions like hypertension, diabetes, short-sightedness, etc as well as cigarette smoking and alcohol consumption. The diagnosis is made through some ophthalmologic investigations which include Tonometry to measure the pressure in the eye, visual field test to check the loss of peripheral vision, slit lamp biomicroscopy, gonioscopy, etc.
The first line of treatment here is the use of medication. The common medication here includes the prostaglandin analog like latanoprost. These drugs increase the uveoscleral outflow since it is the only open drainage channel here. This helps to reduce the intraocular pressure and halt the damage to the retinal ganglion cells. Other drugs that can be given to reduce intraocular pressure include the miotics like pilocarpine which contracts the ciliary muscles, the beta blockers like Timolol, carbonic anhydrase inhibitors like methazolamide, etc.
Surgical options are the next available treatment options when medical treatment fails. The options here include the Argon Laser Trabeculoplasty (ALT) or the Selective Laser Trabeculoplasty (SLT) both of which are used to reduce the intraocular pressure by increasing the aqueous outflow through the trabecular meshwork. Trabeculectomy can also be done where the surgeon creates a hole in the trabecular meshwork to increase drainage. Other surgeries that can be done include minimally invasive glaucoma surgery and glaucoma drainage devices.
By U.S. Navy photo - Public Domain, Wikimedia
The second type of primary glaucoma is Primary Angle Closure Glaucoma. Here, there is the blockage of both the trabecular meshwork and the uveoscleral outflow. Therefore, it occurs acutely and it is a medical emergency. There is a sudden onset of eye pain, lacrimation, nausea, vomiting, seeing of haloes around lights, and blurring of vision. This occurs due to the anterior shifting of the iris too close to the cornea that it closes off the drainage channels at the iridocorneal angle (the angle between the iris and the cornea).
Females are generally more affected than males and it occurs at the age of 40 years and above. Race and family history also plays an important role. Intense emotional stress, staying in a poorly lighted room, trauma, etc have been found to precipitate the occurrence of acute angle closure glaucoma. The treatment here also involves using drugs to lower the intraocular pressure as fast as possible and also surgeries can be done when necessary.
The third type of glaucoma is secondary glaucoma which has an identifiable cause. The cause of glaucoma here is known and can be from trauma to the eye, Tumours in the eye which cause the rise in the intraocular pressure, bleeding in the eye (intraocular hemorrhage), glaucoma due to steroid use, glaucoma due to the formation of new blood vessels in the eye, etc. To treat this type of glaucoma is to treat the cause. Once the cause is identified and treated, glaucoma resolves.
In summary, glaucoma can easily lead to blindness when it is left to go on for a long time, especially open-angle glaucoma which goes on silently causing damage to the eye. Therefore, a regular eye check is very important to detect it early and halt the progression before it leads to total vision loss.
Thanks so much for reading.
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