How they work

Light (from the sun or an artificial light source) travels in a straight line. It bounces off objects and into our eyes. Light first passes through the cornea, the clear, dome-shaped surface that covers the front of the eye. The cornea bends (refracts) the incoming light, which then passes through the pupil. The iris, the coloured part of the eye, regulates the size of the pupil by stopping too much light entering the eye when it is bright and maximising the amount of light entering the eye when it is dark. The light then passes through the lens, which focuses the light onto the back surface of the eye, the retina. The eye changes the shape of the lens as we look at far or near objects to keep them in focus – this is called accommodation.

The retina is the thin, delicate, photosensitive tissue that lines the back of the eye. It contains “photoreceptor” cells that convert light into electrochemical signals. The signals are processed and travel from the retina to the brain through the optic nerve, a bundle of about one million nerve fibres. The brain processes the signal to create the image that you see. The image received on the retina is actually upside-down – as an infant our brains learn to invert the image so we don’t get confused.

Learn more about the parts of the eye and how they work together to allow you to see.

Anatomy and function of the eye

Caring for your eyes

It is important that you know your family’s eye health history; has anyone been diagnosed with a potentially hereditary disease or condition? This will help to determine if you are at higher risk for developing an eye disease or condition. Thereafter, incorporate care of your eye health into your regular daily routine and your annual health care check-up.

Have a comprehensive dilated eye exam

The painless test is one of the best things you can do to make sure that your eyes are healthy. The test looks for common vision problems and early stages of eye diseases that have no obvious early warning signs, such as glaucoma, diabetic eye disease and age-related macular degeneration. Regular comprehensive eye exams can help you protect your sight and make sure that you are seeing your best. The American Academy of Ophthalmology recommends that everyone gets a baseline eye examination at age 40 – follow up screening will depend upon the results of the baseline exam – and annual/biennial eye examinations from age 65.

Eat well

Eating a diet rich in fruits and vegetables, particularly dark leafy greens such as spinach, kale, or collard greens is important for maintaining healthy eyes. Research has also shown there are eye health benefits from eating fish high in omega-3 fatty acids, such as salmon, tuna, and halibut.

Maintain a healthy weight

Being overweight or obese increases your risk of developing diabetes and other systemic conditions; this can lead to vision problems such as diabetic eye disease or glaucoma.

Stop smoking (or better still, never start!)

Similar to the rest of your body, smoking is bad for your eyes. Smoking is linked to an increased risk of developing age-related macular degeneration, cataracts, and optic nerve damage, which can all lead to blindness.

Wear sunglasses

Sunglasses protect your eyes from the sun’s harmful ultraviolet rays. When purchasing sunglasses look for ones that block 99 to 100 percent of both UV-A and UV-B radiation.

Wear protective eyewear

Protective eyewear (safety glasses and goggles, safety shields, and eye guards) are designed to provide the correct protection for potentially dangerous activities, both at work and during recreational activities.

Reduce eye strain

If you spend a lot of time at the computer you sometimes forget to blink and your eyes can get fatigued. Try the 20-20-20 rule: Every 20 minutes, look away from the screen across the room (about 6 metres/20 feet in front of you) for 20 seconds.

Clean your hands and your contact lenses properly

To avoid the risk of infection, always wash your hands thoroughly before putting in or taking out your contact lenses. Make sure to disinfect contact lenses as instructed and replace them as appropriate.

Several cookbooks have been written providing nutritious every-day recipes promoting eye health

A Feast For Your Eyes
Eating for Your Eye Health
Feast Your Eyes on This

Risk factors for eye disease

Vision impairment – when a person’s sight cannot be improved with glasses or contact lenses – should not be considered an unavoidable part of the natural ageing process. It is more than the loss of ability to read letters on a chart; it affects our ability to see in the dark and the speed at which we can read. Vision impairment is generally caused by an eye disease or some type of trauma. The term ‘eye disease’ encompasses a wide range of conditions including age-related macular degeneration, cataract, diabetic retinopathy, glaucoma, retinitis pigmentosa, refractive errors (myopia, hyperopia, presbyopia, astigmatism), colour blindness.

It is important that you know your family’s eye health history; has anyone been diagnosed with a potentially hereditary disease or condition? This will help to determine if you are at higher risk for developing an eye disease or condition. In addition to hereditary factors, there are a number of recognised risk factors that play a role in the development of some eye diseases. These include tobacco use, alcohol consumption, diet and diet-related issues, eye infections, ageing/age, ultraviolet (UV) damage, injuries and accidents, and medication side effects.

Age-related macular degeneration (AMD)

occurs because of damage of the photoreceptor cells in the macular region of the retina as a result of aging. The damage resulting in AMD is accentuated by risk factors  such as tobacco use, genetics, hypertension, heart disease and poor diet. People of Caucasian descent are much more likely to get AMD than those of African descent.


is diagnosed when the lens of the human eye is shadowed and prevents clear vision. People with a diabetic family history have a high-risk factor for developing cataracts. Other factors include aging, smoking and alcohol use, eye infections, UV damage, injuries and accidents, high myopia, ocular hypertension, steroid medicines, and family history.

Diabetic retinopathy

is a complication resulting from diabetes, where progressive damage occurs in the vascular cells of the retina. All people with diabetes – both type 1 & type 2 – are at risk. The longer a person has diabetes, the greater the chance of developing diabetic retinopathy. High blood pressure, elevated glycaemia levels, pregnancy, elevated serum lipid levels, and sometimes genetic and nutritional factors play a role in diabetic retinopathy.


is damage to the eye’s optic nerve as a result of an increase in the pressure within the eye. Smoking, aging, alcohol consumption, eye infections, poor nutrition, UV damage, injuries and accidents, hypertension, ocular hypertension, diabetes, and people with a family history of glaucoma are among the various factors associated with increased risk of glaucoma.

Retinitis pigmentosa (RP)

is a term that refers to group of hereditary disorders that affect the retina’s ability to respond to light. The condition primarily affects rod cells—the photoreceptor cells that are responsible for night vision, seeing in dim light, and peripheral vision. RP may be caused by mutations in any one of at least ten different genes. Recent research findings suggest that in some forms of RP prolonged, unprotected exposure to sunlight may accelerate vision loss.

Refractive error

is the term used when light from an image is not perfectly focussed on their retina. Depending on the severity of the deviance this can lead to a person needing to wear glasses. Myopia, also known as near-sightedness or short-sightedness, is where light focuses in front of the retina. A short-sighted person can see things close-up but has trouble seeing things further away. Hyperopia also known as far-sightedness or long-sightedness is where light focuses behind the retina. A long-sighted person struggles to see near objects but can see distant objects. Presbyopia is a natural part of the aging process, due to hardening of the lens of the eye, causing the eye to focus light behind rather than on the retina. Adults are affected by presbyopia or hyperopia. Myopia can affect both children and adults. If parents have one or two of the refractive errors, it is more likely their children will be affected.

Colour Blindness or colour vision deficiency (CVD)

is a condition where a person’s eyes are unable to see colours under normal light. The retina contains approximately 6 million retinal cone cells. Each cell is ‘colour specific,’ responding mainly to light of specific frequencies. The three different types of cone cells correspond to the three primary colours: red, green and blue. Colour blindness affects millions of people worldwide. It affects 1 in 12 men and 1 in 200 women. The condition ranges from a variety of classes, red-green colour blindness being the most common. Most people who suffer from colour blindness are not blind to colour, but have a reduced ability to see them. CVD can be acquired, but most are inherited genetically.

Courtesy: National Eye Institute, National Institutes of Health (NEI/NIH)

Eye Care Professionals (ECP)

If there is a suspicion that you have an eye disease, you need to visit an Eye Care Professional (ECP). The ECP that you need will depend upon your symptoms and your geography – how eye care is managed within your local healthcare environment. In some countries you can make an appointment directly with an optometrist/ophthalmologist while in other countries you will have to be referred by your family doctor or by an optician/optometrist. ECPs are largely grouped into 3 categories:

An optician

a health care professional who is trained to supply, prepare, and dispense optical appliances through interpretation of written prescriptions. An optician fits and finishes eyeglass lenses and frames and may also dispense low vision devices, contact lenses, and artificial eyes.

An optometrist

a health care professional who specializes in function and disorders of the eye, detection of eye disease, and some types of eye disease management. An optometrist conducts eye examinations, prescribes corrective contact lenses and glasses, and diagnoses and treats eye diseases and disorders.

An ophthalmologist

a medical physician who specializes in the medical and surgical care of the eye and the prevention of eye disease. An ophthalmologist diagnoses and treats refractive, medical, and surgical problems related to eye diseases and disorde

If you need help to identify a suitable ECP in your area here are some useful tips.

Finding an ECP in your area

Questions for your ECP

Communicating clearly with your Eye Care Professional (ECP) is essential for both of you to understand one another and to ensure that you are getting the best advice relevant to your individual circumstances. Asking questions and understanding your ECP’s responses is essential to good communication.

It is sometimes recommended that you bring a family member with you too – two pairs of ears are better than one – particularly where the family member is acting as a caregiver. Caregivers may also need to ask for advice and the best person to ask is the ECP. Additionally, while caregivers will discuss their loved one’s care with the ECP, they seldom talk about their own health, which is equally important. Building a partnership with an ECP that addresses the health needs of the individual and their caregiver, as applicable, is crucial. Ideally the responsibility for the partnership is shared between the affected individual, their caregiver, the ECP and any other healthcare professionals.

When meeting with your ECP it is important to be prepared to get the most out of these appointments. Make a list of your most important concerns and problems. Issues you might want to discuss are changes in symptoms, medications or general health, specific help or concerns that the caregiver has, etc. Remember the ECP only sees a moment in time; make sure you let them know of any concerns that exist in the routine daily environment. Remember also to enlist the help from all of those involved in your care, including nursing staff and pharmacists. Other organisations, such as local patient organisations and support groups can help too.

Make sure your appointment with your ECP meets your needs

Questions for your ECP

Checking your eye health

There are a number of simple tests that can be performed in the comfort of your home to help you to identify potential vision problems that demand professional attention. However, care must be taken when interpreting self-test results, as these tests are not designed to pick up all problems, e.g. blind spots, peripheral vision issues, intra-ocular pressure, etc. Please remember that these tests are not a substitute for regular dilated eye exams conducted by your Eye Care Professional.

The Amsler Grid

This is a test for macular degeneration. You may use it to monitor your vision between visits to your ECP. The test consists of a grid of squares. Wearing your normal corrective lenses you test each eye one at a time. With one eye covered and the grid at arm’s length from you, look at the centre of the grid. If your eye is functioning properly, you should be able to see the centre white dot and the four corners and sides of the grid. The lines should appear to be straight and continuous from top to bottom and side to side. Any or worsening distortion in the grid should be discussed with your ECP.

It is worth noting that reading glasses may interfere with the grid. If you wear glasses consult with your ECP to establish a baseline view of the Amsler Grid against which any changes and deterioration may be measured.

The Ishihara Test

This is a colour perception test for red-green colour deficiencies. The test consists of a number of coloured plates, called Ishihara plates, each of which contains a circle of dots appearing randomized in colour and size. Within the pattern are dots which form a number or shape clearly visible to those with normal colour vision, and invisible or difficult to see to those with a red-green colour vision defect. Other plates are intentionally designed to reveal numbers or shapes only to those with a red/green colour vision deficiency, and to be invisible to those with normal red/green colour vision.

The Visual Acuity Test

Typically performed using a standardized Snellen chart, this is an eye exam that checks how well you see the details of a letter or symbol from a specific distance. Visual acuity refers to the ability to discern the shapes and details of the things you see. You may need an eye exam if you feel you’re experiencing a vision problem or your vision has changed. Children frequently take visual acuity tests. Early testing and detection of vision problems can prevent issues from getting worse. Optometrists, driver’s license bureaus, and many other organizations use this test to check your ability to see. Visual acuity is expressed as a fraction: having 20/20 vision means that your visual acuity at 20 feet away from an object is normal. A person with 20/40 vision must be 20 feet away to see an object that people can normally see from 40 feet away.

Here are some simple tests that can be performed in the comfort of your home to help you to identify potential vision problems. Remember these are not designed to pick up all problems and are not a suitable substitute for regular dilated eye exams.

Amsler Grid
Ishihara Test
Solution - Ishihara Test
Snellen Test