Module 3: Eye Diseases

3.1 Conjunctivitis(1)

Conjunctivitis is a relatively common condition, often referred to as pink eye, in which the conjunctiva (a clear membrane lining the eyeball and inner eyelids) becomes inflamed.

High Risk Groups:
Anyone, but children more so than adults because they spend more time in school where the risk of catching conjunctivitis is higher.

 Causes & Consequences:
There are three type of conjunctivitis:

Pink eye does not normally cause loss of vision, especially when treatment is administered in a timely manner. However, if bacterial conjunctivitis is serious and left untreated, it may damage the eye permanently, leading to loss of vision.

Signs & Symptoms:


Treatment:


Prevention:

3.2 Corneal Diseases & Transplantation

The Cornea: Its Structure

The cornea is a dome-shaped transparent layer that covers the front of the eye. The cornea is made up of several layers as follows:

The Epithelium (Outermost layer):

Bowman’s Membrane (2nd layer):

The Stroma (3rd layer):

Descemet’s membrane (4th layer):

The Endothelium (Innermost layer):

One important function of the cornea is working with the lens to focus the light that enters the eye onto the retina. Disease, infection, or injury to the cornea can interfere with this process, leading to blindness.

The Cornea: Its Function(2)

Common Symptoms of a Corneal Disorder:(3)

Causes & Consequences:(4)

Some threats to the cornea include:

For more information, please visit http://www.nei.nih.gov/health/cornealdisease/

Diagnosis & Treatment:

A person showing symptoms of corneal disease should see an ophthalmologist for a thorough eye examination. The kind of treatment used varies with the nature of the corneal disorder.

Prevention:(5)

Some general guidelines to prevent corneal disease,

Corneal Transplantation(6)

A cloudy cornea impedes the passage of light into the eye to the retina, resulting in poor vision or possibly even blindness. In this case, a corneal transplantation, which involves a surgical procedure to replace diseased cornea with a clear cornea, is necessary. The clear cornea is normally donated through an eye bank.

In a corneal transplant, a cutting instrument called a trephine is used to take out the diseased cornea. The new cornea is sewn into the opening using very fine thread. Eye drops must be applied over the next few months to aid the healing process. Thanks to modern technological advances, corneal transplantation is performed with a high success rate and has restored sight to many who otherwise have been blind.

Corneal Donation

Corneal transplantation surgery would not be possible without donors who have donated  corneal tissue. The transplantation process depends upon the priceless gift of corneal donation from one human to the next. Donated human eyes and corneal tissue are used for research, education, and transplantation.

When consent for donation is given, corneas must be surgically removed within twelve hours of the donor’s death. Very few conditions, such as infectious disease, exclude individuals from donation. Cataracts, poor eyesight, or age do not prevent an individual from being a donor.

The need for corneal tissue is never satisfied. With advances being made in artificial corneas, donations tend to be reserved for patients who require donor cornea transplantation. Success rates are higher with donor corneas.

If you wish to become a donor, you should first consult your family, as the hospital would not normally approach a family for an eye donation from a recently deceased.

3.3 Diabetes & Diabetic Retinopathy

Some Diabetes Facts from the World Health Organization:(7)

Causes & Consequences of Diabetes:(8)

Diabetes is caused by the inability of the pancreas to produce enough insulin (type 1 diabetes), or the inability of the body to utilize the insulin it produces (more common type 2 diabetes).  Insulin is needed to convert sugars into energy. When the body cannot use insulin properly, blood sugar increases, leading to serious damage to nerves and blood vessels, which can in turn cause heart attack and stroke, kidney & eye diseases as well as blindness.

Diabetes can lead to diabetic retinopathy, an eye complication in which the blood vessels in the retina, the light-sensitive tissue, is damaged, causing loss of vision.

Signs & Symptoms:

According to the American Diabetes Association, the following are the symptoms of diabetes:(9)

In the early stages of diabetic retinopathy, there are usually no symptoms. A diabetic person should go for a comprehensive dilated eye exam at least once a year.(10) In the advanced stages of the disease, internal bleeding of the eye can occur, and patients may see spots or experience severely blurred vision.

A Diabetic Retina



Treatment and Prevention

Diabetes must be treated in order to keep blood sugar within normal range and to prevent life-threatening complications. The diabetic individual must watch his diet closely and perform regular exercise in order to maintain normal weight. The doctor may also prescribe oral diabetes medications and insulin.

Diabetic retinopathy is treated with laser surgery to stop the bleeding and prevent new blood vessels from growing in the eye. Treatment may cause some loss of central vision and reduced night vision.

3.4 Glaucoma(11)

According to the World Health Organization, glaucoma affects nearly 65 million people worldwide, making it one of the leading causes of blindness.(12)

High Risk Groups:

African Americans over 40; everyone over 60, especially Mexican Americans; people with a family history of glaucoma

Causes & Consequences:

Glaucoma is caused by an increase in fluid pressure inside the eye, leading to irreversible damage to the eye’s optic nerve. This causes a loss of peripheral vision, or the ability to see the edges of the visual field, eventually leading to blindness.

There are several different forms of glaucoma:

 

Signs & Symptoms:

In the early stages of the disease, vision is normal, and there are no symptoms. The following symptoms appear later:


Treatment:

If detected and treated early, the damage can be minimized or avoided. The following treatment options are available:

Early Detection & Prevention:

If a person belongs to the high risk group, he should go for a comprehensive dilated eye exam at least once every two years.

3.5 Macular Degeneration(13)

Macular degeneration is the gradual loss of vision caused by the oxidation of the macula, which is a small, circular light-sensitive membrane at the center of the retina responsible for our central vision. When the macula degenerates, central vision deteriorates, resulting in dark spots and cloudiness.

High Risk Group:

Older people, worsens with age

Causes & Consequences:

It is caused by the oxidation of the macula. As the arteries harden with age, the delicate structures of the eye begin to lose some of their function. The condition may be aggravated by factors such as smoking, cardiovascular disease, exposure to sunlight, high blood pressure, high cholesterol, diabetes, or poor diet. Heredity may also influence the development of macular degeneration. The condition is very rare before age 50.

There are two types of age-related macular degeneration:

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Signs & Symptoms:

Treatment & Prevention:

3.6 River Blindness or Onchocerciasis

 

“The World Health Organization's (WHO) expert committee on onchocerciasis estimates the global prevalence is 17.7 million, of whom about 270,000 are blind and another 500,000 have visual impairment. About 99% of infected persons are in Africa; the remainder is in Yemen and six countries in the Americas.”(14)

High Risk Group:

River blindness mostly affects individuals in Africa, who live in rural villages situated next to streams where blackflies breed in running water.(15)

Causes & Consequences:

River Blindness is caused by a parasitic worm (Onchocerca Volvulus), which infects blackflies. The disease is transmitted when the infected black-fly bites a person, infecting the person’s body with the larvae.(16) Infected persons may suffer from eye lesions, which can progress to blindness.(17)

Signs & Symptoms:

The affected individual may not display symptoms, but he may have skin rash, eye lesions and bumps under the skin.(18)

Treatment:

A skin biopsy can be done to identify the presence of the disease. An oral medicine, Ivermectin, is administered as treatment.(19)

Prevention:

There is no vaccine to prevent river blindness.(20) However, several preventative measures can be taken to control river blindness:

3.7 Trachoma

“Trachoma affects about 84 million people of whom about 8 million are visually impaired…It is responsible, at present, for more than 3% of the world’s blindness but the number keeps changing due to the effect of socio-economic development and current control programmes for this disease. In spite of this, trachoma continues to be hyperendemic in many of the poorest and most remote poor rural areas of Africa, Asia, Central and South America, Australia and the Middle East.”(23)

Causes & Consequences:

Caused by a bacterial infection of the eye with Chlamydia trachomatis, trachoma can easily spread from person to person, especially in crowded and unsanitary living conditions. A person can get the infection through contact with the eye, nose and throat secretions from an affected individual. If left untreated, the infection leads to irreversible blindness.(24)

Signs & Symptoms:

Trachoma causes the eyelid to turn inwards, which causes the eyelashes to scratch the front part of the eyeball, scarring it. The affected individual eventually becomes blind.(25)

Treatment:

As with most bacterial eye diseases, trachoma can be cured with antibiotics. Eyelid surgery to limit corneal scarring may be necessary.(26)

Prevention:

There are a few preventative measures that can be taken:

Go To Module 4: The Scourge of Eye Health: Vitamin A Deficiency >>

Footnotes

(1) Adapted from Haddrill, Marilyn. "Pink Eye - What Symptoms?/Is it Contagious?/How to Treat it." allaboutvision. Aug 2008. Access Media Group LLC. 8 Jul 2009 <http://www.allaboutvision.com/conditions/conjunctivitis.htm>.

(2) "Cornea (Eyes): Conditions, Symptoms, and Treatments Information on Medicinenet.com." MedicineNet.com. MedicineNet. 8 Jul 2009 <http://www.medicinenet.com/corneal_disease/article.htm>.

(3) Ibid.

(4) Adapted from "Facts About the Cornea and Corneal Disease [NEI Health Information]." National Eye Institute. May 2009. National Institutes of Health. 8 Jul 2009

(5) Adapted from "Cornea (Eyes): Conditions, Symptoms, and Treatments Information on Medicinenet.com." MedicineNet.com. 25 May 2005. MedicineNet, Inc.. 8 Jul 2009 <http://www.medicinenet.com/corneal_disease/page2.htm>.

(6) Hill, Jessica. "Cornea Transplant (Corneal Transplant or Penetrating Keratoplasty) - AllAboutVision.com." allaboutvision. May 2007. Access Media Group LLC. 8 Jul 2009 <http://www.allaboutvision.com/conditions/cornea-transplant.htm>.

(7) "WHO/Diabetes." World Health Organization. Nov 2008. World Health Organization. 8 Jul 2009 <http://www.who.int/mediacentre/factsheets/fs312/en/index.html>.

(8) "WHO/Diabetes." World Health Organization. World Health Organization. 8 Jul 2009 <http://www.who.int/dietphysicalactivity/publications/facts/diabetes/en/>.

(9) "Diabetes Symptoms - American Diabetes Association." American Diabetes Association. American Diabetes Association. 8 Jul 2009 <http://www.diabetes.org/diabetes-symptoms.jsp>.

(10) "Facts About Diabetic Eye Disease [NEI Health Information]." National Eye Institute. Apr 2006. National Institutes of Health. 8 Jul 2009 <http://www.nei.nih.gov/health/diabetic/retinopathy.asp>.

(11) "Facts About Glaucoma [NEI Health Information]." National Eye Institute. Apr 2006. National Institutes of Health. 8 Jul 2009 <http://www.nei.nih.gov/health/glaucoma/glaucoma_facts.asp>.

(12) "World Glaucoma Day Warns Public of Blindness Risks." National Glaucoma Research. 10 Mar 2009. American Health Assistance Foundation. 8 Jul 2009 <http://www.ahaf.org/glaucoma/newsupdates/world-glaucoma-day-warns.html>.

(13) Haddrill, Marilyn. "Macular Degeneration - A Complete Guide from All About Vision." AllAboutVision. Jun 2007. Access Media Group LLC. 8 Jul 2009 <http://www.allaboutvision.com/conditions/amd.htm>.

(14) "Division of Parasitic Diseases - Onchocerciasis/River Blindness Fact Sheet." Centers for Disease Control and Prevention. 11 Sep 2008. Centers for Disease Control and Prevention. 8 Jul 2009 <http://www.cdc.gov/ncidod/dpd/parasites/onchocerciasis/factsht_onchocerciasis.htm>.

(15) "Division of Parasitic Diseases - Onchocerciasis/River Blindness." Centers for Disease Control and Prevention. 11 Sep 2008. Centers for Disease Control and Prevention. 8 Jul 2009 <http://www.cdc.gov/ncidod/dpd/parasites/onchocerciasis/default.htm>.

(16) "WHO/Onchocerciasis." World Health Organization. World Health Organization. 9 Jul 2009 <http://www.who.int/topics/onchocerciasis/en/>.

(17) "Division of Parasitic Disease - Onchocerciasi/River Blindness." Centers for Discease Control and Prevention. 11 Sep 2008. Centers for Disease Control and Prevention. 9 Jul 2009 <http://www.cdc.gov/ncidod/dpd/parasites/onchocerciasis/default.htm>.

(18) "WHO/Onchocerciasis." World Health Organization. World Health Organization. 9 Jul 2009 <http://www.who.int/topics/onchocerciasis/en/>.

(19) "Division of Parasitic Disease - Onchocerciasis/River Blindness." Centers for Disease Control and Prevention. 11 Sep 2008. Centers for Disease Control and Prevention. 9 Jul 2009 <http://www.cdc.gov/ncidod/dpd/parasites/onchocerciasis/factsht_onchocerciasis.htm>.

(20) Ibid.

(21) "WHO/Onchocerciasis." World Health Organization. World Health Organization. 9 Jul 2009 <http://www.who.int/topics/onchocerciasis/en/>.

(22) "Division of Parasitic Disease - Onchocerciasis/River Blindness." Centers for Disease Control and Prevention. 11 Sep 2008. Centers for Disease Control and Prevention. 9 Jul 2009 <http://www.cdc.gov/ncidod/dpd/parasites/onchocerciasis/factsht_onchocerciasis.htm>.

(23) "WHO/Priority Eye Diseases." World Health Organization. World Health Organization. 9 Jul 2009 <http://www.who.int/blindness/causes/priority/en/index2.html>.

(24) "WHO/Trachoma." World Health Organization. World Health Organization. 9 Jul 2009 <http://www.who.int/topics/trachoma/en/>.

(25) Ibid.

(26) Solomon, Anthony W and Hugh Ringland Taylor. "Trachoma: Treatment & Medication." emedicine 05 Sep 2007 Web.09 Jul 2009. <http://emedicine.medscape.com/article/1202088-treatment>.

(27) West, Sheila K.. "Blinding Trachoma: Prevention With the Safe Strategy." The American Journal of Tropical Medicine and Hygiene 17 Sep 2003 18-23. Web.9 Jul 2009. <http://www.ajtmh.org/cgi/content/full/69/5_suppl_1/18?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=Blinding+Trachoma%3A+Prevention+with+the+SAFE+Strategy&andorexactfulltext=and&searchid=1103212282200_556&stored_search=&FIRSTINDEX=0&sortspec=relevance&resourcetype=1&journalcode=tropmed>.

(28) Ibid.