Eye Health Summary
Eye Health Summary
Important disclaimer: The information on Unite For Sight's website and contained in the Unite For Sight Online Eye Health Course is for educational purposes only and should not be considered to be medical advice. It is not meant to replace the advice of a physician. All medical advice and information should be considered to be incomplete without a physical exam, which is not possible without a visit to your doctor.
Eye Anatomy:
The human eye works like a living camera. Like a camera, the eye processes light and takes mental snapshots of images, which are then developed in the brain. In order to create vision, all parts of the eye must work together as a team. The cornea, the clear, film-like part of the eye, is the leader. When light enters the dark pupil of the eye, the cornea bends it. The refracted light travels to the lens behind the pupil. The lens changes its shape to adjust the focus on both distant and near objects. This process is known as accommodation. The cornea is a critical part of the eye, and in certain circumstances, if the cornea is damaged, it may need to be replaced through a transplant.
The lens projects light from the outside world as an inverted image into the retina, which then acts like film in a camera and captures the image. The image is sent to the brain in the form of electric impulses to be developed.
Parts of the Eye:
Sclera: The outer, white part of the eye that gives protection to the delicate inner structures.
Iris: The colored part of the eye that contains very fine muscles that control the size of the pupil.
Pupil: The little black spot in the center of the iris that controls the amount of light reaching the retina by expanding in the dark to allow more light in, and contracting in the light to prevent excess light from entering.
Aqueous humor: A fluid produced by the ciliary body that circulates through the front and rear of the eye to maintain eye pressure and provide nourishment to the cornea and the lens.
Macula: A tiny part of the retina that focuses and produces color vision.
Ciliary body: Contains a gland that secretes aqueous humor and a muscle that contracts and expands to control the curvature of the lens.
Optic disc: The point where the retina meets the optic nerve, which is often referred to as the blind spot because of its insensitivity to light.
Vitreous gel: A clear gel that fills the eye and provides it with a spherical shape.
Choroid: Located between the sclera and the retina, it is made up of blood vessels that provide nourishment to the eye.
Zonulae: Threadlike structures that attach the lens to the ciliary muscle and help it to change its curvature.
Vision Defects:
Nearsightedness (myopia)
What is it?
A person who has myopia can clearly see objects that are near, but objects that are far appear blurred.
What are the symptoms?
Myopic patients see objects at a distance as quite blurry, and often squint to see far-away objects.
How is it acquired or spread?
Myopia is caused by a refractive problem of the cornea or lens, or the eyeball is too long. It cannot be spread between people.
How is it treated or prevented?
Corrective lenses (glasses or contacts) are used to improve myopia. It is critical that these distance glasses are provided by health care professionals, rather than volunteers or trained community members.
Who does it affect?
Myopia can affect anyone.
Farsightedness (hyperopia)
What is it?
A person with hyperopia can clearly see objects that are far away, but objects that are near appear blurred.
What are the symptoms?
Near objects appear blurry, and patients may be found squinting to see objects at a close distance.
How is it acquired or spread?
Hyperopia is caused by a malfunction in the cornea or lens, or the eyeball is too short. It cannot be spread between people.
How is it treated or prevented?
Reading glasses can correct a person’s near vision. Like distance glasses, these readers must be distributed by optometrists and eye care professionals. Otherwise, patients may receive glasses that do not help, or they might not realize that they need additional care, especially if they have other vision impairment. Eyeglasses are tremendously helpful, but are not a panacea – they do not solve all vision problems. Thus, a comprehensive exam from an eye doctor is crucial.
Who does it affect?
Hyperopia can affect anyone.
Cataract
What is it?
Cataract is the leading cause of blindness worldwide, affecting about 20 million people. A cataract is formed when the lens becomes clouded.
What are the symptoms?
Cataracts can cause blurry vision, poor night vision, or sensitivity to light.
How is it acquired or spread?
Although commonly a result of aging (senile cataract), some people are born with them (congenital cataract). Trauma, medication, and long-term inflammation can also cause cataracts.
How is it treated or prevented?
Treatment can involve extraction and replacement of the lens. Sunglasses can help to prevent cataracts. Research has shown that cataract surgery has a far-reaching impact on the quality of life for the elderly. Further, “[r]estoration of vision that accompanies most cataract operations reduces both psychiatric and somatic symptoms."(1) For example, nursing home residents who underwent cataract surgery because of functional problems experienced significant improvements in their quality of life, in addition to dramatically improved vision.(2) Following cataract surgery, many individuals are able to once again engage in productive activities such as business, farming, or maintaining the household. In addition, many experience an increased level of independence after surgery, better communication ability, and stronger social relationships.
Who does it affect?
Cataracts can affect anyone, especially the elderly.
“Over the past twenty years, the major advance in the treatment of cataract has been the worldwide availability of low-cost, good-quality intraocular lenses (IOLs) since the early 1990s. Their routine use has resulted in an increase in both the quality of visual outcome for patients (as shown by population-based rapid assessment of cataract surgical services) and the willingness of surgeons to perform cataract surgery at an earlier time, before blindness has developed… There is evidence that, since the introduction of IOLs, there has been an increase in cataract surgical rates around the world, and particularly in low-income countries.”(3)
Glaucoma
What is it?
Glaucoma is a condition resulting from too much aqueous humor present in the eye, causing the pressure to rise and push against the optic nerve, resulting in nerve damage and vision loss.
What are the symptoms?
Glaucoma is detected based on intraocular pressure testing and examination of the aqueous drainage system, but because there are no early warning signs and vision loss is so gradual, a person may not realize that he/she is becoming blind.
How is it acquired or spread?
Glaucoma is not contagious, but can be hereditary.
How is it treated or prevented?
Early detection is the key to successful treatment, but there is no cure for glaucoma, as damage done to the optic nerve is permanent. However, treatment can minimize the effects of glaucoma, and prevent further damage.
Who does it affect?
Glaucoma is particularly prevalent among the elderly, people with a family history of the disease, those who are nearsighted, and people of African descent.
Diabetic retinopathy
What is it?
Diabetic retinopathy is the condition in which the blood vessels at the back of the eye become weak and burst.
What are the symptoms?
A person may have the beginning stages of diabetic retinopathy without knowing it, as it does not affect vision in the early onset.
How is it acquired or spread?
Diabetic retinopathy is caused by diabetes, and is not contagious.
How is it treated or prevented?
Diabetic retinopathy can be prevented through a healthy diet and lifestyle including foods that have complex carbohydrates instead of fats and sugars. Fruits and vegetables are important to prevent diabetes, as is regular exercise.
Who does it affect?
This affects patients with diabetes.
Macular degeneration
What is it?
Macular degeneration is a condition in which central vision is lost due to the deterioration of the macula, a part of the retina where most of the light focuses.
What are the symptoms?
Macular degeneration will cause a patient to lose central vision slowly, though peripheral vision may remain. Other symptoms include bent or warped images, dark, foggy, or light spots, and words on a page may appear distorted or incomplete.
How is it acquired or spread?
Age-related macular degeneration is hereditary, and is the most common form. Patients are not contagious.
How is it treated or prevented?
Sunglasses can help to prevent macular degeneration, as can cardiovascular health, regular blood pressure, avoidance of smoking and diabetes, and a healthy diet. Only certain types of macular degeneration are treatable, usually with photodynamic therapy and medication.
Who does it affect?
Macular degeneration is a large cause of disability in older people, lowers patients’ quality of life, and is a risk factor for depression. “Until recently, the emotional impact of AMD was rarely addressed, leaving patients with few options for coping. Fortunately, there has been a recent interest in the psychosocial consequences of AMD and blindness in general, and this research underscores the extent of the disability caused by eye diseases”.(4)
Amblyopia
What is it?
This condition, also known as "lazy eye," occurs when one eye is weaker than the other. Both eyes cannot blend an image.
What are the symptoms?
Symptoms can include frequent squinting or closing one eye to see, poor visual acuity, eye strain, headaches, eyes that do not move together or fix on the same point, crying in children, or complaining when one eye is covered, cloudiness in the pupil, and drooping of the upper eyelid.
How is it acquired or spread?
Lazy eye usually starts at childhood, and can be corrected if detected and treated by the age of five. It is caused by a lack of brain stimulation from the weaker eye, forcing the strong eye to become dominant. The amblyopic eye is suppressed and may become blind.
How is it treated or prevented?
Glasses to align or focus the eyes
Surgery on the eye muscles
Eye exercises
Wearing a patch on the stronger eye, forcing the amblyopic eye to work, developing more connections with the brain
Atropine drops can be placed in the strong eye to blur its vision temporarily and stimulate the weak eye
Who does it affect?
This can affect anyone, particularly those with misaligned or crossed eyes, those with a different visual acuity between the two eyes, and those who have one eye that is nearsighted, farsighted, astigmatic, or has cataract.
Vitamin A deficiency (xerophthalmia)
What is it?
An eye disease caused by a deficiency in Vitamin A, xerophthalmia is a range of disorders that can eventually lead to blindness.
What are the symptoms?
Symptoms include Bitot’s spots (foamy, soapy, and whitish patches on the white part of the eye that can affect sight at night), conjunctival xerosis (dryness and wrinkling of the white part of the eye), corneal lesions (lesions that cover the clear part of the eye, causing blindness), night blindness and difficulty seeing things in dim light, blindness, and weakened teeth, bones, and immune system.
How is it acquired or spread?
Xerophthalmia is acquired when the patient lacks a sufficient amount of Vitamin A.
How is it treated or prevented?
Xerophthalmia is prevented by a diet high in Vitamin A, which maintains health cells in various structures of the eye, and is required for converting light into nerve signals in the retina. Prevention strategies include breastfeeding (this is a natural source of Vitamin A), Vitamin A supplements, food fortification (adding Vitamin A to foods like oil, sugar, milk, and flour), and Vitamin A-rich foods, including liver, egg yolk, milk products, butter, small fish, and dark green leaves.
Who does it affect?
Xerophthalmia can affect anyone, especially those without access to Vitamin A-rich foods.
Trachoma
What is it?
Trachoma is an eye infection that scars the upper eyelid and causes it to go inward, resulting in the eyelashes scratching the cornea. This can be a slow, painfully blinding condition.
What are the symptoms?
Symptoms include tearing, pain, swollen eyelid, corneal inflammation, scratching of eyelids, scars, and potentially blindness.
How is it acquired or spread?
Trachoma is a communicable infection that spreads through direct contact with the eye, nose, and throat secretions from affected individuals. It can be prevented by proper hygiene.
How is it treated or prevented?
Trachoma can be treated by surgery or antibiotics.
Who does it affect?
Anyone can get trachoma, especially those living in communities with limited access to hygienic practices, such as safe water and sanitation.
River blindness (onchocerciasis)
What is it?
River Blindness is caused by a parasite spread by black flies that breed in rivers and deposit the larvae of the worm onto the person they bite.
What are the symptoms?
Symptoms can include severe itching and eye lesions, eventually leading to blindness.
How is it acquired or spread?
The disease is acquired through bites from black flies, often prevalent in Africa.
How is it treated or prevented?
River Blindness can be treated by medication, sometimes requiring the removal of nodules. It can be prevented by wearing full sleeve or protective clothing, spraying insecticide along riversides and fast-flowing waters to control the black fly population, and prophylactic medications.
Who does it affect?
River Blindness is predominant in certain African countries.
Conjunctivitis (pink eye)
What is it?
Conjunctivitis is an eye infection that targets the conjunctiva, the outermost eye layer that covers the sclera.
What are the symptoms?
Symptoms include itchiness, tearing, eye discomfort, redness, and discharge from the eye, sometimes causing the eyelids to stick together.
How is it acquired or spread?
There are three types of conjunctivitis. The viral strain is caused by an upper respiratory infection, cold, or sore throat. Allergic conjunctivitis is caused by intolerance to chemical substances such as cosmetics or drugs. Last, bacterial conjunctivitis stems from a bacterial infection.
How is it treated or prevented?
Conjunctivitis is fairly easy to treat with antibiotics, eye drops, or ointment for a bacterial infection. Viral or allergic conjunctivitis can be treated by bathing the eyes in water, antihistamines, or special eye drops.
Who does it affect?
Anyone is susceptible to conjunctivitis.
Color blindness
What is it?
Color blindness describes problems in recognizing various colors and shades of color. Normal color vision requires cones, which are in the retina of the eye. An abnormality or lack of any of the types of cones results in color blindness.
What are the symptoms?
Colorblind individuals cannot distinguish some colors, such as red and green or blue and yellow.
How is it acquired or spread?
Colorblindness is usually inherited. Aging, certain medications, and retinal or optic nerve disease may interfere with normal color vision.
How is it treated or prevented?
There is no cure for patients whose color deficiency has been present since birth. Some cases of color deficiency that begin later in life may be helped with surgery, changing medication, or treating the eye disease that caused the color deficiency.
Whom does it affect?
Color blindness can affect anyone, but is far more prevalent among males.
Pterygium
What is it?
Pterygium is a wedge-shaped, raised outgrowth of the conjunctiva.
What are the symptoms?
Symptoms include irritation, redness, sensitivity to light, tearing, foreign body sensation, double vision, and increased astigmatism.
How is it acquired or spread?
Pterygium is not contagious, and is often caused by continued exposure to UV-rays.
How is it treated or prevented?
Pterygium can be prevented by protecting eyes from sun, dust, and wind. Artificial tears and topical steroids may be helpful in reducing symptoms.
Whom does it affect?
Pterygium is especially common in the 20-30 year age group, particularly in males. It is predominant in tropical climates with exposure to ultraviolet light.
Presbyopia
What is it?
Presbyopia (farsightedness) is the world’s most common cause of visual impairment, primarily due to the difficulty for impoverished patients to obtain eyeglasses to treat the condition.(5)(6)
What are the symptoms?
Individuals with presbyopia have difficulty seeing objects that are near. They will likely also squint to see close-by objects.
How is it acquired or spread?
Presbyopia is caused when the light entering the cornea and crystalline lens is bent so that the image focuses behind the retina, distorting the image transmitted to the retina and brain.
How is it treated or prevented?
Wearing corrective lenses (glasses or contacts) improves presbyopia. Because presbyopia is progressive, patients will continually need to renew their eyeglasses prescriptions as they age.(7) Long-term access to eye care is essential to treating presbyopia. Additionally, patients are at higher risk for developing permanently sight-threatening conditions such as glaucoma and diabetic eye disease, making comprehensive eye care all the more essential.(8)
Who does it affect?
Presbyopia is prevalent among adults over 40 years of age. Presbyopia has significant effects on quality of life, particularly in the developing world, making corrective glasses a necessity. Those with functional presbyopia report higher dissatisfaction with their general health, difficulty in carrying out daily tasks, and increased problems with family relationships. Women are affected disproportionately, due to increased prevalence and severity of presbyopia among women and because presbyopia makes tasks traditionally performed by females such as sewing, knitting, and cooking in poor light very difficult. Uncorrected presbyopia impedes efforts to improve adult literacy, which is associated with higher life quality.(9)
Eye Safety:
Prolonged or improper exposure to sun rays can cause damage to the eyes, as well as damage to the skin. UVB radiation threatens the outside portions of the eye: the cornea, conjunctiva and crystalline lens, causing irritation, dryness, inflammation (keratitis) and precocious aging (photo-aging). UVA radiation is the most harmful to both the skin and eyes because the rays are shorter and able to penetrate furthest into the eye, damaging the retina.
Cataracts and macular degeneration are the most common eye diseases caused by the sun. Like skin diseases caused by exposure to sunlight, the eye disorders develop gradually over many years.
The use of protective sunglasses that can screen UV rays should begin during childhood. By minimizing the exposure to solar radiation, it is possible to prevent the damage to ocular tissues and delay the development of ultraviolet-related eye diseases.
Other eye injuries most often include chemicals in the home, workshop and tool parts, battery acid, sports accidents, fireworks, over-exposure to ultra violet (UV) radiation, and the use of toys and games without supervision. Common eye injuries and symptoms include:
Blunt trauma
Penetrating injuries
Orbital “foreign body” injury
Corneal injuries or abrasions
Radiation injuries
Chemical burns
Prevention of eye injuries includes the following strategies:
Keep a pair of goggles in the home, land and car
Always check spray nozzles before using household chemicals
Wash hands well after handling chemicals
Check for debris, rocks, stones, low-hanging branches before using a lawnmower or trimmer
Look around the home for potential hazards to eyes, such as protruding objects, sharp corners, etc.
Keep adults' and children's fingernails short
In the industrial workplace, wear appropriate safety eyewear always. Welders, plumbers, construction laborers, machine operators and carpenters should learn about safety eyewear for their occupation. Polycarbonate lenses are best.
Wear sunglasses that block both UVA and UVB rays to prevent radiation injury from UV light. Always wear special goggles when using a tanning bed. Higher UV exposure occurs on snow, sand, and water, concrete and in high altitudes and low latitudes. UV radiation is highest between 10 am and 4 pm and highest in spring and summer.
Children and adults should use sunglasses if they are involved in ANY contact sport, or sport that involves use of a racquet, bat or other equipment such as a hockey stick. Sports eye protectors with polycarbonate lenses should be worn for sports such as basketball, racquet sports, soccer, baseball fielders, lacrosse and field hockey. Boxing, wrestling and other full contact martial arts sports have a high risk of serious eye injury. Thumbless gloves may reduce the number of boxing eye injuries. Contact lenses offer NO protection when participating in sports.
There are NO safe ways for non-professionals to use any fireworks, including sparklers. Use of legal or illegal fireworks is strongly discouraged due to the very high numbers of eye injuries that occur.
Make sure gifts that you give to small children do not have sharp, protruding or projectile parts. Darts, bow and arrows, and guns can cause severe eye injuries or blindness.
To prevent further damage to the eye after an injury, seek medical care immediately. Never rub the eye, apply ointment, or remove an object from the eye. Flush chemical injuries with water or saline (salt) solution.
In order to prevent visual impairments including cataract, macular degeneration, and glaucoma, it is imperative to avoid cigarette smoke. Studies show that cigarettes contribute to the formation of cataracts in two ways. First, free radicals present in tobacco smoke assault the eye directly, potentially damaging lens proteins and the fiber cell membrane in the lens.(10)(11) Second, smoking reduces the body's levels of antioxidants and certain enzymes which may help remove damaged protein from the lens.(12)(13) Over time, this damage from smoking can double or triple an individual's risk of developing cataracts.(14)
Testing Visual Acuity:
The following video will help you learn how to test visual acuity, but this will also be reviewed on outreach.
Questions:
Include answers to the following questions in your typed response.
If someone has myopia, do they have trouble seeing things far away, or near?
If someone has hyperopia, do they have trouble seeing things far away, or near?
My grandmother’s eyes look cloudy and gray. What condition might she have?
What kind of glasses will help my father’s cataract?
My aunt fears cataract surgery because she believes it involves replacing her eye with an animal’s eye. What does the actual procedure involve?
My grandfather was diagnosed with glaucoma, and is losing his vision. Should he have surgery?
My doctor said that I have diabetic retinopathy, but my vision seems fine – is this possible? If so, what can I do to prevent visual impairment in the future?
I want to encourage my mother to take her medication: how might macular degeneration negatively affect her life?
My son seems to have a lazy eye – what might cause this? Will it just go away on its own?
My doctor says that I’m deficient in vitamin A – how will this impact my health, and what foods can I eat to ameliorate this?
My friend has trachoma – do I need to take extra precautions around her? If so, what kind?
My daughter’s eye is red and swollen, and sometimes she can’t open it. Will glasses help her? If not, what will?
I was diagnosed with Pterygium, but I’m only 25! I’m a farmer and work daily in the fields – are there precautions I could take to prevent it from getting worse?
My aunt was diagnosed with presbyopia five years ago and received glasses, but now they don’t seem to be working. Why is this, and what should she do?
Footnotes
(1) Fagerström R. Correlation between depression and vision in aged patients before and after cataract operations. Psychol Rep1994;75:115–25.
(2) Owsley C, McGwin G Jr, Scilley K, Meek GC, Seker D, Dyer A. Impact of cataract surgery on health-related quality of life in nursing home residents. Br J Ophthalmol 2007;91:1359–63.
(3) Foster, A., Gilbert, C., and Johnson, G. “Changing patterns in global blindness: 1988-2008.” Community Eye Health. 21.67 (2008): 37-39.
(4) Casten RJ, Rovner BW, Tasman W. Age-related macular degeneration and depression: a review of recent research. Curr OpinOphthalmol 2004;15:181–3.
(5) Holden, B.A., Fricke, T.R., Ho, S.M., Song, R., Schlenther, G., Cronjé, S., Burnett, A., Papas, E., Naidoo, K.S. and Frick, K.D. “Global Vision Impairment Due to Uncorrected Presbyopia.” Archives of Ophthalmology. 126.12 (2008): 1731-1739.
(6) Sherwin, J.C., Keeffe, J.E., Kuper, H., Islam, F.M.A., Muller, A., and Mathenge, W. “Functional Presbyopia in a Rural Kenyan Population: The Unmet Presbyopic Need.” Clinical & Experimental Ophthalmology. 36.3 (2008): 245-251.
(7) “Refraction Training Manual: Presbyopia.” 2007. International Centre for Eye Health. www.cehjournal.org. http://www.cehjournal.org/files/refractiontraining/07.asp.
(8) Holden, B.A., Fricke, T.R., Ho, S.M., Song, R., Schlenther, G., Cronjé, S., Burnett, A., Papas, E., Naidoo, K.S. and Frick, K.D. “Global Vision Impairment Due to Uncorrected Presbyopia.” Archives of Ophthalmology. 126.12 (2008): 1731-1739.
(9) Patel, I., Munoz, B., Burke, A.G., Kayongoya, A., Mchiwa, W., Schwarzwalder, A.W., and West, S.K. “Impact of Presbyopia on Quality of Life in a Rural African Setting.” Ophthalmology. 113.5 (2006): 728-734.
(10) McCarty CA, Nanjan MB, Taylor HR. Attributable risk estimates for cataract to prioritize medical and public health action. Invest Ophthalmol Vis Sci 2000;41:3720–25.
(11) Van Heyningen R, Pirie A. Naphthalene cataract in pigmented and albino rabbits. Exp Eye Res 1976;22:393–94.
(12) Shalini VK, Luthra M, Srinivas L et al. Oxidative damage to the eye lens caused by cigarette smoke and fuel smoke condensates. Indian J Biochem Biophys 1994; 31:261–66.
(13) Wegener A, Kaegler M, Stinn W. Frequency and nature of spontaneous age-related eye lesions observed in a 2-year inhalation toxicity study in rats. Ophthalmic Res 2002; 34:281–87.
(14) Kelly SP, Thornton J, Edwards R, et al. Smoking and cataract: review of causal association. J Cataract Refract Surg 2005;31:2395–404.