Module 2: Eye Conditions

2.1 Amblyopia or “Lazy” Eye

Amblyopia is a condition in which one eye has less vision because the brain favors visual input from the other eye.(1)

High Risk Group:

A common cause of visual problems in childhood, amblyopia affects 2 to 3 out of every 100 children. If not treated in early childhood, it can persist into adulthood, causing monocular (affecting one eye) visual impairment.(2)

Signs & Symptoms:(3)

Causes & Consequences:(4)

Treatment & Prevention:(5)

In order to treat amblyopia, the patient must create a stronger link between the weak eye and the brain by:

Early detection and subsequent treatment of the problem in children can help to prevent permanent loss of vision.

2.2 Cataracts(6)

"According to the latest assessment, age related cataract is responsible for 48% of world blindness, which represents about 18 million people. Although cataracts can be surgically removed, in many countries surgical services are inadequate, and cataract remains the leading cause of blindness.”(7) – World Health Organization

In a cataract patient, the lenses of the eyes become clouded, blocking the passage of light to the light-sensitive retina.

High Risk Group:

Mostly in older people, as the lens grows cloudy with age.

Signs & Symptoms:

According to the Mayo clinic, the following are the signs and symptoms:(8)

----------------Healthy Eye --------------------------------- Eye with a Cataract--------------------

Causes & Consequences:

Treatment:

Treatment involves a simple surgical procedure, which replaces the affected lens with an artificial one. This procedure has a high rate of success.

 Prevention:

--------Actual Cataract Removed by a Surgeon--------

2.3 Color Blindness

Color blindness is a problem in seeing color. When light falls on the retina, light-sensitive photoreceptors are activated, sending electrical signals to the brain. The brain “interprets” the signals to enable a person to see color. There are two kinds of photoreceptors, namely the rods (which transmit mostly black and white information to the brain) and cones (which are sensitive to light of different wavelengths, and thus colors). There are three kinds of cones, each sensitive to red, green, or blue light. If one or more of these types of cones fail to function properly or are absent, color vision is impaired.(9) 

High Risk Group:

Color blindness is more common in males than females because it is sex-linked, meaning that it comes from the X-chromosome which is passed from a mother to her son.(10)

Signs & Symptoms:(11)

Causes & Consequences:(12)

 

Detection, Diagnosis & Treatment:
Color blindness is detected using special colored charts with lots of colored dots. Some of these colored dots form a number, and the patient is asked to identify the number.(13) Unfortunately, inherited color blindness cannot be cured. However, if a cataract or other eye diseases or conditions are causing problems with color vision, treating those problems may restore normal color vision. Children must be diagnosed earlier on for color blindness to prevent learning difficulties in school.

2.4 Pterygium(14)

Pterygium is a wedge-shaped, raised outgrowth that forms over the conjunctiva and grows onto the corneal surface.

Signs & Symptoms:

Causes & Consequences:

Treatment & Prevention:

Surgery is the only way to remove a pterygium, and unfortunately, it may grow back. Protecting eyes from sun, dust and wind is essential. Artificial tears may be helpful to reduce irritation and sensation of a foreign body in the eye, and topical steroids may be used to diminish inflammation.

2.5 Refractive Error

Refractive errors are the most common eye conditions. In order to see clearly, the light that enters the eye must be bent by the cornea and the lens and focused properly onto the retina. The retinal cells then generate electrical impulses that travel along the optic nerve to the brain. If the light is not refracted correctly, a blurred image results. There are four common types of refractive errors:(15)

2.5.1 Myopia (Near-sightedness)(16)

A nearsighted person can see near objects but objects further away appear blurred.

Signs & Symptoms:

Causes & Consequences:

The eyeball is too long so that light rays entering the eye focus in front of the retina rather than on the retina, causing blurry vision. Myopia runs in families. People who practice poor reading habits like reading in dim light may also develop myopia.

Treatment:

Prevention:
Myopia cannot be prevented, but eye health can be maintained by eating foods rich in vitamins A & C, wearing sunglasses outdoors to protect the eyes from UV radiation, wearing goggles when working with hazardous chemicals, having regular eye exams etc.

2.5.2 Hyperopia (Far-sightedness)(17)

A farsighted person can see distant objects clearly but close objects appear blurred.

Signs & Symptoms:

Causes & Consequences:

Eyeball is too short or the cornea too flat, so that light rays entering the eye focus behind the retina rather than directly on it. 

Treatment:

Prevention:

Myopia cannot be prevented, but eye health can be maintained by eating foods rich in vitamins A & C, wearing sunglasses outdoors to protect the eyes from UV radiation, wearing goggles when working with hazardous chemicals, having regular eye exams etc. 

2.5.3 Astigmatism(18)

To a person with astigmatism, objects that are near and objects that are far away appear blurred.

Signs & Symptoms:

Causes & Consequences:

Astigmatism may be hereditary. It can also be acquired through an injury to the lens or cornea. Diabetes causes high blood sugar levels which change the shape of the lens, leading to astigmatism.

Treatment & Prevention:

2.5.4 Presbyopia(19)

Presbyopia is similar to hyperopia or far-sightedness, in that the affected individual cannot focus on near objects properly.

Signs & Symptoms:

Causes & Consequences:

As a person ages, his lens loses elasticity, or its ability to expand, and hence cannot resume the shape it needs to focus on near objects. Only distant objects are seen clearly.

Treatment:

Prevention:

Presbyopia cannot be prevented because it is a natural part of the aging process of the eye.

Go To Module 3: Eye Diseases >>

Footnotes


(1) "Facts About Amblyopia [NEI Health Information]." National Eye Institute. Jul 2009. National Institutes of Health. 7 Jul 2009 <http://www.nei.nih.gov/health/amblyopia/amblyopia_guide.asp>.

(2) Ibid.

(3) "Amblyopia." St. Luke's Eye. St. Luke's Eye. 7 Jul 2009 <http://www.stlukeseye.com/Conditions/Amblyopia.asp>.

(4) "Facts About Amblyopia [NEI Health Information]." National Eye Institute. Jul 2009. National Institutes of Health. 7 Jul 2009 <http://www.nei.nih.gov/health/amblyopia/amblyopia_guide.asp>.

(5) Ibid.

(6) "WHO - Priority Eye Diseases." World Health Organization. World Health Organization. 7 Jul 2009 <http://www.who.int/blindness/causes/priority/en/index1.html>.

(7) Ibid.

(8) Mayo Clinic Staff, "Cataracts: Symptoms - MayoClinic.com." MayoClinic.com. Mayo Clinic. 7 Jul 2009 <http://www.mayoclinic.com/health/cataracts/DS00050/DSECTION=symptoms>.

(9) "Color Blindness: Causes, Symptoms, Diagnosis, and Treatment." WebMD. 31 Oct 2007. WebMD. 8 Jul 2009 <http://www.webmd.com/eye-health/tc/color-blindness-topic-overview>.

(10) "Color Blindness: More Prevalent Among Males." Howard Hughes Medical Institute. Howard Hughes Medical Institute. 8 Jul 2009 <http://www.hhmi.org/senses/b130.html>.

(11) "Color Blindness - color vision." StLukesEye.com. St. Luke's Eye. 8 Jul 2009 <http://www.stlukeseye.com/conditions/ColorBlindness.asp>.

(12) "Causes of color blindness." essortment. PageWise. 8 Jul 2009 <http://www.essortment.com/all/colorblindness_rkes.htm>.

(13) "Color Blindness - color vision." StLukesEye.com. St. Luke's Eye. 8 Jul 2009 <http://www.stlukeseye.com/conditions/ColorBlindness.asp>.

(14) Fisher, Jerome P and William B Trattler. "Pterygium." emedicine 12 Jan 2009 Web.08 Jul 2009. <http://emedicine.medscape.com/article/1192527-overview>.

(15) "Refractive Errors (Blurred vision)." visionchannel. 08 Aug 2007. Healthcommunities.com, Inc.. 8 Jul 2009 <http://vision.healthcommunities.com/refractiveerrors/index.shtml>.

(16) Adapted from "Myopia or Nearsightedness - visionchannel." visionchannel. 04 Dec 2007. Healthcommunities.com, Inc.. 8 Jul 2009 <http://vision.healthcommunities.com/refractiveerrors/myopia.shtml>.

(17) Adapted from "Myopia or Nearsightedness - visionchannel." visionchannel. 04 Dec 2007. Healthcommunities.com, Inc.. 8 Jul 2009 <http://vision.healthcommunities.com/refractiveerrors/myopia.shtml>.

(18) Adapted from "Vision Correction Surgery Options, LASIK & Others - visionchannel." visionchannel. 08 Aug 2007. Healthcommunities.com, Inc.. 8 Jul 2009 <http://vision.healthcommunities.com/refractivecorrection/surgery.shtml >.

(19) Adapted from "Presbyopia - Problem with Close Vision, Age-Related - visionchannel." visionchannel. 08 Aug 2007. Healthcommunities.com, Inc.. 04 Dec 2007 <http://vision.healthcommunities.com/refractiveerrors/presbyopia.shtml>.