Glaucoma: Eye Biology, Nerve Damage, and Recent Research

Updated on January 2, 2018
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Linda Crampton is a teacher with a first class honors degree in biology. She writes about human biology and the scientific basis of disease.

A healthy eye with efficient drainage of fluid is important for vision.
A healthy eye with efficient drainage of fluid is important for vision. | Source

What Is Glaucoma?

The word “glaucoma” refers to a group of eye problems that involve damage to the optic nerve. This nerve transmits signals from the retina at the back of the eyeball to the vision centre of the brain, which creates an image. In many cases of glaucoma, the pressure inside the eyeball is increased. This injures the optic nerve and causes loss of vision.

Glaucoma can generally be treated once it's discovered. At the moment, however, the optic nerve can't be repaired and any vision that has been lost before the diagnosis can't be restored. The cause of the disorder isn’t completely understood. A better understanding of the disease could lead to improved treatments. Recent research may be very significant in this regard.

Internal anatomy of the eye
Internal anatomy of the eye | Source

The numbers in the eye shown above represent the structures named below. Though Schlemm's canal is one structure, in places it consists of more than one passageway. 1 = sclera, 2 = choroid, 3 = Schlemm's canal, 4 = iris root, 5 = cornea, 6 = iris, 7 = pupil, 8 = anterior chamber, 9 = posterior chamber, 10 = ciliary body, 11 = lens, 12 = vitreous chamber, 13 = retina, 14 = optic nerve, 15 = suspensory ligament

Circulation of Fluid in the Eye

In a healthy eye, a liquid known as aqueous humour is secreted by the ciliary body into the posterior chamber of the eye. This chamber is located between the suspensory ligament and the back of the iris, as shown in the illustration above. The liquid comes from blood plasma. It moves through the pupil (an opening in the middle of the iris) and into the anterior chamber. The anterior chamber is located between the front of the iris and the cornea.

The aqueous humour is an essential liquid for the health and functioning of the eye. It contains nutrients for the eye and removes waste substances and debris. It also help the eye to maintain its shape, which is necessary for effective light transmission.

The aqueous humour drains from the anterior chamber into a spongy, sieve-like tissue known as the trabecular meshwork. The drainage area is located in the angle between the cornea and the iris. The fluid travels from the trabecular meshwork into the Schlemm's canal, then into connector channels, and finally into the bloodstream. Aqueous humour is continually being secreted from the blood and then drained back into it.

Aqueous humour secretion and drainage
Aqueous humour secretion and drainage | Source

One problem with illustrations that show a flat section of the eye is they may give the viewer a false impression. For example, in the two illustrations shown above, it looks as though the "angle" is present at only two places in the eye. In reality, because the iris and the cornea are circular, the angle is, too.

The eye as viewed from the front
The eye as viewed from the front | Source

The iris is the coloured part the the eye and is circular. It's covered by the transparent cornea. The sclera is the white part of the eye.

Drainage Problems in the Eye

In many people with glaucoma, the drainage system described above doesn’t work properly. The aqueous humour isn’t drained from the eyes fast enough or is blocked from entering the trabecular meshwork. As a result, the pressure in the area increases. This pressure is transmitted to the vitreous chamber of the eye, which holds a gel known as the vitreous humour. Unlike the aqueous humour, the vitreous humour is a permanent material and isn’t created and drained. The increased pressure in the eye (the intraocular pressure) injures the optic nerve.

Glaucoma generally develops in older people but sometimes appears in younger ones. Some people develop increased pressure in their eyeball without developing glaucoma. Others have glaucoma without increased pressure in their eyeball. These observations add to the mysteries of the disease. The disease is more common in people who have specific disorders, including hypertension (high blood pressure) and diabetes.

Symptoms of glaucoma don't appear until the disease is at an advanced stage. It's important to get eyes checked regularly so that the disease can be recognized at an early stage and vision loss stopped.

Fluid Drainage in the Eye and Glaucoma

Types of Glaucoma

Multiple types of glaucoma exist. The names of the different types sometimes vary, which can cause confusion. The classification system given below is used by John Hopkins Medicine in the United States and the National Health Service in Britain.

Open Angle (or Primary Open Angle)

Open angle glaucoma is by far the most common type of the disease. Its name is derived from the fact that the angle between the cornea and the iris is wide, as it should be. The condition is thought to be caused by the drainage canals being slowly clogged or by death of cells in the drainage area. These factors lead to increased pressure in the eyeball. In some cases, however, the intraocular pressure is normal and the problem is believed to arise due to a different reason. Some organizations classify this variation as normal tension glaucoma.

Angle Closure (or Narrow Angle)

Some people have unusual eye anatomy in which the structures around the drainage area are crowded together. The angle between the cornea and the iris is narrow. This puts a person at risk for angle closure glaucoma. The condition develops suddenly when the iris is pushed over the drainage area by pressure of some kind. Intraocular pressure may then increase rapidly, damaging the optic nerve. Immediate medical attention is essential in order to retain vision.

Secondary

Secondary glaucoma is produced by another condition. This condition may be an eye injury, a particular medication, a particular type of surgery, or disorders that cause long-term and widespread inflammation.

Childhood (Congenital or Developmental)

Congenital glaucoma is diagnosed in babies and young children up to the age of around three. The condition is present at birth, but its effects may not be noticed immediately. It's caused by a problem in the development of the eye's drainage system. The sooner the disorder is diagnosed and treated, the better the outcome.

An Overview of Glaucoma

Peripheral vision is lost first in glaucoma. Central vision isn't lost until the disease is at a very advanced stage.

Layers of the retina
Layers of the retina | Source

Optic Nerve Damage

The retina consists of layers. The rods and cones (R and C in the simplified diagram above) are stimulated when struck by light energy. An electrical signal is then transmitted through the cell layers of the retina and along the optic nerve to the brain.

The retinal ganglion cells (G) are neurons (nerve cells) located at the back of the retina. Their extensions or axons (Ax) travel along the bottom of the retina at about an angle of ninety degrees and eventually form the optic nerve. This leaves the eye in an area known as the optic disc (or the head of the optic nerve), which is labelled in the illustration below. In glaucoma, the retinal ganglion cells and the optic disc are damaged. This means that the electrical signal is hindered in its journey from the rods and cones to the brain.

Interior of the eye
Interior of the eye | Source

Vision loss caused by glaucoma can't be reversed, but further damage to eyesight can often be prevented. The goal of most treatments is to reduce the amount of aqueous humour that's made or to help it drain. Treatments generally involve special types of eye drops, oral medications, or surgery. Eye drops and medications may cause side effects. Some types of surgery may cause complications or need to be repeated over time.

Potential Benefit of Lipoxins

Current glaucoma treatments deal with problems within the eye. It would be wonderful to find a treatment that prevents further damage to the optic nerve. Researchers may have discovered a substance that can do this. It should be noted that the research described in the studies mentioned below was performed with rodents. The news is certainly hopeful, but further research involving clinical trials in humans is needed.

Researchers from the University of California, Berkeley and the University of Toronto have discovered that specific lipoxins are anti-inflammatory and neuroprotective in rats and mice. The chemicals are secreted by astrocytes, star-shaped cells located around neurons. (Since we are mammals like rats and mice, we have astrocytes that produce lipoxin, too.) Lipoxins A4 and B4 are the kinds that are beneficial with respect to glaucoma.

According to the researchers, in glaucoma the astrocytes are injured and stop their production of the helpful lipoxins. As a result, the optic nerve is damaged. The scientists found that administering lipoxins to rats and mice with glaucoma stopped the degeneration of retinal ganglion cells. The researchers suspect that the lipoxins will eventually be useful for humans with glaucoma and perhaps for people with other neurodenerative diseases.

A simulation of vision loss in glaucoma
A simulation of vision loss in glaucoma | Source

At present, there is no cure for glaucoma, which is estimated to affect 80 million people worldwide.

— Yasmin Anwar, News Release from the University of California, Berkeley

Function of Schlemm's Canal

One of the frustrations of dealing with glaucoma is that its cause isn't fully understood. Multiple causes may exist. Researchers at Korea's Center for Vascular Research in the Institute of Basic Science have made some potentially significant discoveries. The scientists' research suggests that problems in the Schlemm's canal may be responsible for some cases of glaucoma.

Like other cells in the body, the endothelial cells in the wall of the Schlemm's canal contain vacuoles, or sacs. Some of the vacuoles in the canal cells are unusually large. They transport aqueous humour across the wall of the canal and towards the bloodstream. They therefore play a vital role in maintaining normal pressure in the eye.

Proteins and a Receptor in Schlemm's Canal

The Korean scientists' research was centred on proteins named angiopoietins. The specific angiopoietins that the researchers investigated are named Ang1 and Ang2. Proteins often bind to receptors on the cell membrane in order to trigger a particular activity. Ang1 and Ang2 bind to a receptor called Tie2. This binding is known to be important in the Schlemm's canal.

Effects of Decreased Tie2

The researchers found that mice with insufficient Tie2 in their eye had a high intraocular pressure, damage to neurons in their retina, and partial loss of vision. In addition, they had a greatly decreased number of large vacuoles in the endothelial cells of their Schlemm's canal, suggesting that they were experiencing problems in draining liquid from their eye.

Observations in Older Mice

The risk of glaucoma in humans increases as people age. Interestingly, the scientists found that compared to younger mice, older ones has a decreased level of large vacuoles, Tie2, Ang1, and Ang2. They also had a lower level of Prox1, another protein involved in the activity of angiopoietin and Tie2.

Angipoietin/Tie2 and Glaucoma

Experimental Treatments in Mice

Yet more evidence supports the idea that the angiopoietin-Tie2 receptor system may be involved in glaucoma, at least in mice. The researchers injected an antibody named ABTAA into one eye of mice but not into the other. ABTTA stands for Ang2-binding and Tie2-activating antibody. One week after the treatment, the eye that had received the antibodies had an increased number and size of large vacuoles in the Schlemm's canal and a higher level of Tie2 and Prox1 compared to the values in the eye that didn't receive treatment.

Even more significantly, when the antibody was given to mice with primary open angle glaucoma, in addition to the results observed above, intraocular pressure decreased. This suggests that the antibody could be used as a medicine.

Some researchers are exploring the possibility of treating glaucoma with stem cells. These unspecialized cells can be triggered into producing specialized ones. It may one day be possible to create new cells for the eye's drainage system or new retinal ganglion cells.

Understanding Glaucoma and Improving Treatment

Human biology is complex. This is especially true at the microscopic level, where a myriad of processes occur to maintain life and keep our bodies functional. Understanding these processes can be challenging.

It's good that we have some treatments for glaucoma. Improved methods of dealing with the disease are needed, however. Fully understanding the cause or causes of glaucoma could be a huge help in the treatment of eye and nerve damage that has already occurred, the prevention of further damage, and the prevention of the disease altogether.

References

© 2018 Linda Crampton

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    • AliciaC profile image
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      Linda Crampton 3 days ago from British Columbia, Canada

      I appreciate your comment, Nithya. Early detection is certainly important.

    • Vellur profile image

      Nithya Venkat 3 days ago from Dubai

      A detailed and clear explanation about glaucoma and the ongoing research. Early detection will sure help save eye vision. Thank you for sharing.

    • AliciaC profile image
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      Linda Crampton 6 days ago from British Columbia, Canada

      Thank you very much, Devika.

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      DDE 7 days ago

      You shared an important hub on the eye and Glaucoma. Some people don't know this about the eye. Important and useful!

    • AliciaC profile image
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      Linda Crampton 11 days ago from British Columbia, Canada

      Hi, Martie. I agree—medical scientists make some wonderful discoveries. Thank you for the kind comment.

    • MartieCoetser profile image

      Martie Coetser 11 days ago from South Africa

      Thank you, Linda, for this superb informative hub about the eye and Glaucoma. The eye is such a small but extremely complicated organ. I take my hat of to medical scientists.

    • AliciaC profile image
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      Linda Crampton 11 days ago from British Columbia, Canada

      Thank you very much, Natalie. I appreciate your visit a great deal.

    • Natalie Frank profile image

      Natalie Frank 11 days ago from Chicago, IL

      This is such an informative article full of important topics about a serious eye condition. Hopefully, it will help encourage and motivate all of us to keep up with our eye exams regularly. I know I will be scheduling another checkup soon after reading this. Thanks for the article!

    • AliciaC profile image
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      Linda Crampton 13 days ago from British Columbia, Canada

      Hi, Peggy. Yes, it would be horrible to lose vision if this can be prevented. I appreciate your visit.

    • AliciaC profile image
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      Linda Crampton 13 days ago from British Columbia, Canada

      Thank you very much for the visit and the comment, Mary.

    • Peggy W profile image

      Peggy Woods 13 days ago from Houston, Texas

      Good article about glaucoma Linda. This is one of the best reasons I know to regularly visit an eye doctor. As you said glaucoma can be treated if discovered. It would be a shame to lose vision because it went untreated!

    • Blond Logic profile image

      Mary Wickison 13 days ago from Brazil

      It has been quite some time since I've been for an eye exam. I know this is something they routinely check for. Your article explains the disease clearly.

      Well written and researched.

    • AliciaC profile image
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      Linda Crampton 13 days ago from British Columbia, Canada

      I'm sorry your mother has glaucoma, Kari. I hope the potential treatments work in humans and that they are very helpful.

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      Kari Poulsen 13 days ago from Ohio

      My mother recently was diagnosed with Glaucoma. I like hearing about things like ABTAA, it sounds promising.

    • AliciaC profile image
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      Linda Crampton 13 days ago from British Columbia, Canada

      Hi, Audrey. Perhaps your doctor saw features in your eye that increase the likelihood of glaucoma development. I hope that never happens! It's good that you see the specialist regularly so that any probem can be dealt with right away.

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      Audrey Hunt 13 days ago from Nashville Tn.

      A well-written article! I see my eye specialist regularly. Keeping an eye (no pun untended) on one of my eyes for possible glaucoma. not sure what type. I haven't been diagnosed with this disease which leaves me somewhat confused.

    • AliciaC profile image
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      Linda Crampton 2 weeks ago from British Columbia, Canada

      It's interesting to read about people's experiences with glaucoma and its risk. Thanks for the comment and for sharing the information, Heidi. Best wishes for 2018!

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      Heidi Thorne 2 weeks ago from Chicago Area

      Had laser surgery for narrow angle... better than waiting for it to get worse! Excellent and thorough discussion of the issue which so many seem to have. Thanks and Happy New Year!

    • AliciaC profile image
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      Linda Crampton 2 weeks ago from British Columbia, Canada

      Thank you for the comment, Larry. I'm sorry that your brother has passed.

    • Larry Rankin profile image

      Larry Rankin 2 weeks ago from Oklahoma

      My brother, who has passed, was an optometrist. Glaucoma was one of the more serious disorders he had to treat.

      As always, great read. Very educational.

    • AliciaC profile image
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      Linda Crampton 2 weeks ago from British Columbia, Canada

      Hi, Bede. Unfortunately, the tendency to develop the eye diseases that you mention is genetically based in some forms of the disease. This doesn't necessarily mean that we'll get the disease if a relative has it, since environmental factors may be involved as well, but it does indicate that we need to be vigilant with respect to eye health.

    • Bede le Venerable profile image

      Bede 2 weeks ago from Minnesota

      Thanks Linda for the good research and article. My Dad has glaucoma, cataracts, and macular degeneration, which has unfortunately made him legally blind. He's 89 years old, and his mother had the same eye problems. The eye doctor told me that my eyes are healthy, but is there an indication that eye diseases are passed predominantly through one's mother or father?

    • AliciaC profile image
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      Linda Crampton 2 weeks ago from British Columbia, Canada

      That sounds very unpleasant, Larry. I'm sorry you're experiencing pain. I hope you eventually find a better treatment.

    • AliciaC profile image
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      Linda Crampton 2 weeks ago from British Columbia, Canada

      That's an interesting thought, Nadine. I wouldn't be surprised if you're right. It may have had an effect on some people's eyesight. I appreciate your comment.

    • AliciaC profile image
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      Linda Crampton 2 weeks ago from British Columbia, Canada

      Hi, K S Lane. It's nice to meet you! Thanks for the comment.

    • Larry Fish profile image

      Larry W Fish 2 weeks ago from Raleigh

      A great article. Linda. I have a different nerve damage. I have been diagnosed with Trigeminal Neuralgia. I have been getting stabbing pains to my right eye, up to 60 a day for a while. I am now on pain meds and it is somewhat controlled, but not totally.

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      Nadine May 2 weeks ago from Cape Town, Western Cape, South Africa

      Many thanks for that very informative article. I wonder if our eyes have been effected by the computer technology in the last say 20 years?

    • K S Lane profile image

      K S Lane 2 weeks ago from Melbourne, Australia

      I've heard the word 'glaucoma' thrown around a lot, but I've never gone to the trouble to learn what it actually means. Thanks for enlightening me!

    • AliciaC profile image
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      Linda Crampton 2 weeks ago from British Columbia, Canada

      Hi, Dora. Thanks for the visit. It about time that I had my eyes checked again, too!

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      Dora Weithers 2 weeks ago from The Caribbean

      Thanks for the information, the explanations and the warnings. My eyes haven't been checked in a while. After reading this, I'll put the eye check on my agenda.

    • AliciaC profile image
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      Linda Crampton 2 weeks ago from British Columbia, Canada

      Thank you very much for the kind comment, Dianna. I appreciate your visit.

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      Dianna Mendez 2 weeks ago

      This is the first article I've read on glaucoma that brings it out so clearly. I didn't realize it was a disease. Thank you for the education.

    • AliciaC profile image
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      Linda Crampton 2 weeks ago from British Columbia, Canada

      Hi, Manatita. I didn't include much information about current drugs for glaucoma because I wanted to concentrate on the biology of the condition and on new research related to the biology. I'm sorry that you're having problems with your eyes. I'm probably not the best person to discuss the treatments in detail because I don't have a medical background and I have never experienced the condition myself. Best wishes for a complete recovery. I will be thinking of you in February.

    • manatita44 profile image

      manatita44 2 weeks ago from london

      Fascinating! You did not touch on the drugs used and side-effects.

      My eyes are generally irritable and red. I have had a let trabeculectomy, with a right due 15th Feb. Your prayers are needed.

      You have done a very thorough job on this subject. Do something on pre-assessment - preparing for the traeculectomy and the recovery phase. Do it for me. Much Love.

    • AliciaC profile image
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      Linda Crampton 2 weeks ago from British Columbia, Canada

      It sounds like your father-in-law was very lucky with respect to his driving, Jackie. Thank you very much for the comment.

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      Jackie Lynnley 2 weeks ago from The Beautiful South

      My father-in-law had serious problems with this and the family had serious problems with him trying to hide it so he could continue to drive. Thankfully nothing terrible happened although he was in a couple of fender benders and it could have been serious.

      I do hope this helps many see early treatment is so important as with most diseases.

      Fantastic information as usual, Linda!

    • AliciaC profile image
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      Linda Crampton 2 weeks ago from British Columbia, Canada

      I'm glad your eyes were checked and that you don't have glaucoma, Bill. Happy New Year to you, too!

    • AliciaC profile image
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      Linda Crampton 2 weeks ago from British Columbia, Canada

      Hi, Nell. Your plan to get a regular eye exam is a great example to follow. Thanks for the visit.

    • AliciaC profile image
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      Linda Crampton 2 weeks ago from British Columbia, Canada

      I hope so, too. Research could help a lot of people.

    • AliciaC profile image
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      Linda Crampton 2 weeks ago from British Columbia, Canada

      Hi, Mary. I hope better treatments are found, too. Regular eye exams are important. It's time for me to have another one!

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      Bill Holland 2 weeks ago from Olympia, WA

      Well two weeks ago I was assured I do not have this, so good news there. I do have a floater, which is entertaining at times. :) Great information, Linda! Happy New Year to you!

    • Nell Rose profile image

      Nell Rose 2 weeks ago from England

      My aunt had glaucoma, so we always get a check up. I wear contact lenses so get a yearly check. This is great for anyone who needs to know and understand why it happens.

    • Glenn Stok profile image

      Glenn Stok 2 weeks ago from Long Island, NY

      Hi Linda, Thanks for your reply. I didn't realize you were referring to cure for a damaged optic nerve rather than a cure for the glaucoma itself. I agree–Nerves that die from lack of blood due to high pressure cannot be restored. The cure for the ailment needs to be done before damage to the nerve occurs, as you had mentioned in your article.

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      Alexander James Guckenberger 2 weeks ago from Maryland, United States of America

      I hope that funding for research increases.

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      Mary Norton 2 weeks ago from Ontario, Canada

      I do hope that these studies find the treatment as so many people suffer from this. I am one of those who take the eyes for granted and not have regular check up.

    • AliciaC profile image
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      Linda Crampton 2 weeks ago from British Columbia, Canada

      Your mother's experience sounds scary, Flourish. I'm glad that she was helped and hope that she has no problems in the future.

    • AliciaC profile image
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      Linda Crampton 2 weeks ago from British Columbia, Canada

      Hi, Glenn. Thanks for sharing your experience. I'm very glad that your eye pressure has remained normal after your treatment. I think what researchers mean when they say that there is no cure is that damage that has already been done to the optic nerve can't be repaired at the moment. If the problem is discovered and treated before vision is affected or before the optic nerve is damaged, however, I can certainly understand why the treatment could be considered a cure.

    • FlourishAnyway profile image

      FlourishAnyway 2 weeks ago from USA

      This is well researched and explained. My mother developed acute angle glaucoma which I assume is narrow glaucoma after two failed cornea surgeries. Her eye pressure was extremely high and she had to see a glaucoma specialist on a Sunday as an emergency measure. He did an emergency treatment on her and it was resolved but she’ll always need to be careful of pressure issues.

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      Glenn Stok 2 weeks ago from Long Island, NY

      Wonderful article with full detail. Your explanations are right-on Linda.

      I had narrow-angle glaucoma that suddenly developed over ten years ago. It’s also called pigmentary glaucoma because my pigment from my iris rubbed off and clogged the drainage of the aqueous humour.

      You quoted a news release that said there is no cure for glaucoma. But then you later discussed treatments that are being tested on mice. I actually had mine cured.

      I had a procedure done called Laser Iridotomy to control the pressure. A laser is used to make a pinhole in the eye above the iris. I consider that a cure because I never had to use drops anymore after that and my pressure remained normal ever since.

      There sure is a lot of research being done with finding cures for all types of disfunctions of the human body. We live in a good time period where this technology exists.

    • AliciaC profile image
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      Linda Crampton 2 weeks ago from British Columbia, Canada

      I appreciate your comment very much, Louise. Thanks for the visit.

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      Louise Powles 2 weeks ago from Norfolk, England

      Thanks for the information. Your article was really indepth and interesting. I've learned a lot about glaucoma by reading this.

    • AliciaC profile image
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      Linda Crampton 2 weeks ago from British Columbia, Canada

      Thank you very much, Kenna. It's definitely very important to think about our health as we get older!

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      Kenna McHugh 2 weeks ago from Northern California

      As we get older, we have to start thinking about our bodies getting older and keep an eye on our overall health. Great article, it has lots of detailed information.