How eyes 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, light-sensitive 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 of the Eye

The retina consists of a neural layer and a pigmented layer. The neural layer contains photoreceptor cells, the rod and cone cells. These cells collect the light signals directed onto them and send them as electrical signals to the optic nerve. Further details of the cell types found within the neural layer of the retina are provided below.

Microscopic Anatomy of the Retina

Learn more

Rod Cells: Rod cells are concentrated around the edge of the retina. They help us to see things that aren’t directly in front of us, giving us a rough idea of what is around us. They help us with our mobility and getting around, by stopping us from bumping into things. They also enable us to see things in dim light and to see movement.

Cone Cells: Cone cells are concentrated in the centre of our retina where the light is focused by the cornea and lens. This area is called the macula. Cone cells give us our detailed vision which we use when reading and looking at people’s faces. They are also responsible for most of our colour vision.

Retinal Pigment Epithelium (RPE): The retinal pigment epithelium is a layer of cells located just outside the retina and is attached to the choroid

Bipolar Cells: Bipolar cells exist between photoreceptors (rod cells and cone cells) and ganglion cells. They act, directly or indirectly, to transmit signals from the photoreceptors to the ganglion cells.

Ganglion cells: Is a type of nerve cell located near the inner surface of the retina of the eye. It receives visual information from photoreceptors and communicates this to the brain.

What is visual impairment?

Most people who have a visual impairment are able to see something. The level of vision can vary from being able to distinguish between light and dark, to seeing large objects and shapes, to seeing everything but as a blur. Visual impairment is a term used to describe all levels of vision loss. It covers moderate sight loss, severe sight loss and blindness. People are not either sighted or blind; there are different degrees of vision loss and different ways in which it can affect what a person sees. For example, some conditions can affect the peripheral vision, and others can affect the central vision. Vision loss can affect people of all ages and can have an impact on all aspects of a person’s life: social, school and work, and everyday tasks.

What are Inherited Retinal Diseases?

 

Inherited retinal diseases (IRDs; also called “inherited retinal dystrophies or degenerations”) are a diverse group of rare eye diseases, characterised by the progressive loss of function or death of photoreceptor (light-sensitive) cells in the retina, resulting in associated vision loss or blindness. The underlying cause of all IRDs is the presence of a mutation(s) in genes involved in development and normal function of photoreceptors or other retinal cells.

It has been estimated that IRDs affect approximately 1 in every 3000 persons (more than 2 million people worldwide). IRDs can affect people of all ages – they are leading cause of vision loss in people of working age (16 to 64 years) and a common cause of visual impairment in childhood.

Classification of Inherited Retinal Diseases

IRDs can be clinically classified according to the regions of the retina or cell types they primarily affect, their pattern of progression (progressive or stationary), or whether they occur as part of a syndrome (syndromic or non-syndromic).

One type of IRD classification is based on whether they initially cause degeneration of rod or cone cells.

In some disorders, such as cone-rod dystrophy and Stargardt disease, cones start to degenerate first, followed by rods. As cones are primarily located in the centre of the retina, people affected by cone-rod dystrophy or Stargardt disease will initially experience deterioration of their central vision, that over time will gradually spread out to affect their peripheral vision.

Retinitis pigmentosa (RP), on the other hand, is a rod-cone dystrophy where rods start to die first followed by cones later. People affected by RP will initially experience night blindness and tunnel vision (due to loss of rods). As the disease progresses, and cones start to die, their central vision can become affected and this can result in legal blindness.

Leber congenital amaurosis (LCA) is the most severe form of IRD. LCA has one of the earliest onset of the diseases that typically appears in the first few months of life. In LCA, cones and rods start to degenerate at the same time and the supporting layer behind the photoreceptors, the retinal pigment epithelium (RPE), may also be affected.

In diseases where both cones and rods eventually degenerate late in the disease, such as cone-rod dystrophy, RP and Stargardt disease, the loss of both photoreceptor types can make an accurate diagnosis difficult.

In the above examples, the photoreceptor cells progressively degenerate and die. In some types of IRDs, the affected cells do not degenerate and appear intact, however, they do not function correctly. One example is congenital stationary night blindness (CSNB) which is caused by a defect in the rods or cones which affects their ability to transmit signals to neighbouring ganglion cells within the retina. Another example, is Achromatopsia (ACHM), or colour blindness, where one or more of the three types of colour-vision cone cells are dysfunctional but remain intact.

The pattern of disease progression is a second way that IRDs can be classified. IRDs can be progressive (the vision loss begins with few symptoms that get worse over time), or stationary (the visual impairment does not get better or worse over time). RP, cone-rod dystrophy and Stargardt disease are examples of progressive diseases, where vision loss worsens over time due to the progressive degeneration of photoreceptor cells in the retina. Achromatopsia and congenital stationary night blindness are examples of IRDs where the visual impairment does not change over time.

IRDs can also be classified as syndromic or non-syndromic. Non-syndromic vision loss is not associated with other signs and symptoms; vision loss is the only symptom of the disease. An example of non-syndromic vision loss is LCA. In contrast, syndromic vision loss occurs with other symptoms in other parts of the body. An example of syndromic vision loss is Usher syndrome, where both hearing and vision are affected.

Purpose of this toolkit

This toolkit aims to provide information about IRDs to inform and educate people with IRDs, their carers, and the medical and research community with the goal of empowering all stakeholders to advance towards cures.

Information about clinical trials that are currently being conducted worldwide can be found on www.ClinicalTrials.gov and can be searched by condition and trial location.

Genetics of Inherited Retinal Diseases

 

IRDs are caused by a gene mutation that is inherited from a parent. This led to the title of “Inherited Retinal Disease”. In the case of IRDs, the mutation affects genes that play an essential role in normal retinal development and functioning, leading to the degeneration of photoreceptors and other retinal cells and associated vision loss.

Scientific research has shown that IRDs are genetically diverse, with over 260 disease-related genes identified to date. In some cases the genes or mutations responsible are not yet known or not understood. However, ongoing research and genetic testing is advancing our knowledge of such genetic changes in order to find cures.

Genetic testing is of utmost importance for many IRDs due to their genetic origin. Genetic testing can aid in diagnosis and, critically, it can determine if individuals have a specific mutation that may be treatable by specific gene therapies. You can learn more about how genetic testing works, and what it can do, at our toolkit ‘SENDING A RED ALERT!’, intended to inform those with rare eye diseases about genetic testing services: http://www.retina-international.org/toolkit-redalert

You can learn more about inheritance patterns here: http://www.retina-international.org/patients/your-eyes/inheritance-patterns

Watch this short video from the National Eye Institute/National Institutes of Health (NEI/NIH) about vision in families: https://youtu.be/Gz_rAMF7ZHA

Genetic complexity of Inherited Retinal Diseases

A small number of IRDs are caused by mutations in one single gene. For example, Choroideremia (CHM), a progressive condition where vision loss primarily affects males, is caused by a mutation in a gene called CHM. Stargardt disease is caused by a mutation in a gene called ABCA4.

For most other IRDs, affected people may have the same symptoms and the same disease but each person could have mutations in different genes. This is because mutations in many different genes can all have the same end result. For example, RP can be caused by mutations in one of 84 different genes, while cone-rod dystrophy can be caused by mutations in one of 33 different genes. Mutations in 20 different genes can lead to macular dystrophies (MD) and another 15 different genes can be responsible for congenital stationary night blindness.

While mutations in different genes can result in the same disease, different changes in just one gene can sometimes result in different diseases in individuals. For example, different mutations in the GUCY2D gene can result in either cone-rod dystrophy or in LCA. Cone-rod dystrophy can be caused in some individuals by autosomal dominant (ad) variants of GUCY2D while autosomal recessive (ar) variants of the same gene can lead to LCA in other people.

In some instances, the severity of the disease can be affected by different combinations of different types of mutations. A person who has two non-functioning copies of ABC4A will have early-onset cone-rod dystrophy while another person with a combination of two severe and mild variants of ABC4A may have intermediate or late-onset Stargardt disease.

Autosomal recessive retinal dystrophies (arRDs) can be syndromic or non-syndromic. Non-syndromic vision loss is not associated with other signs and symptoms. In contrast, syndromic vision loss involves loss that also occurs with symptoms in other parts of the body. Different mutations in the USH2A gene can cause Usher syndrome type 2 or non-syndromic arRP.

Figure. Genetic diversity of the six major inherited retinal diseases (IRDs). The numbers outside of the ellipses correspond to the number of IRD genes responsible for the specific disease, while numbers within the ellipses correspond either to disease-specific genes or to genes mutated in two or more diseases.

RP: retinitis pigmentosa; LCA: Leber congenital amaurosis; CD/CRD: cone dystrophy/cone-rod dystrophy; CSNB: congenital stationary night blindness; MD: macular dystrophy; EVR: exudative vitreoretinopathy.

Further information
You can find more information about genetics in IRDs
from our YouTube channel

Professor Jane Farrar

Genetics: An Overview

Symptoms, causes and treatment options of different IRDs

 

While all IRDs affect the retina and visual function, the symptoms, onset, progression and cause of each varies. Here, we will give an overview of the different symptoms of the different IRDs in a PDF format that you can easily download. In our “Focus On” section on this website, you can find out more about certain diseases as this Toolkit develops.

Usher syndrome

Usher syndrome is a syndromic IRD that affects both hearing and vision. The symptoms of Usher syndrome consist of hearing loss (found at an early age), vision loss caused by  a condition called retinitis pigmentosa (RP), and sometimes balance problems.

While people with IRDs do have a higher risk of developing hearing issues late in life than the general population, Usher syndrome is characterised by hearing loss early-on in life. You can find more information on Usher Syndrome in our “Focus on: Usher Syndrome” section.

Leber Congenital Amaurosis

Leber congenital amaurosis (LCA) appears at birth or in very young children. It is an inherited disease that can result in quite severe vision loss. The level of vision loss varies between individuals; some people affected can have little or no light perception. Both rod and cone cells are affected by the mutations and both will degenerate and die. You can find more information about LCA in our “Focus on: LCA” section.

Symptoms, causes and treatment options of IRDs

Including:

  • Retinitus Pigmentosa
  • Choroidremia
  • Juvenile Macular Degeneration
  • Stargardt Disease
  • Best Disease
  • Juvenile X-Linked Rentinoschisis
  • Leber Hereditary Optic Neuropathy
  • Cone Rod Dystrophies
  • Achromatopsia
  • Gyrate Atrophy
  • Kearnes-Sayre Syndrome

Detection

 

Given the range of diseases that come under the ‘Inherited Retinal Diseases’ umbrella, and their differing ages of onset, detection can vary. However, the unifying condition is some form of vision loss that can first affect the ability to read, to see the board in school, to see things to the side. In young babies, visual impairments can cause involuntary jerky rhythmic eye movement (nystagmus), sensitivity to light (photophobia), eye-pressing or rubbing with fingers or knuckles.

If you have concerns, the first step is to attend a Health Care Professional that can look at and test your eyes to determine the cause and/or extent of the issues. Please see our sections for more information:

Health care professionalsTaking care of your eyes

Often, one of the issues for someone diagnosed with an IRD is that the diagnosis is not precise. IRDs are very complicated genetic disorders that can be due to mutations in one of more than 200 genes, and sometimes in genes that are still not known. It can be impossible to differentiate between types of IRDs by looking at the eye. Therefore, genetic testing of the affected individual is necessary for the best chance of a complete diagnosis. Genetic screening of the person’s family members can provide more information about the inheritance pattern of the condition and potentially identify others affected. A complete genetic diagnosis is also crucial for admission to an appropriate clinical trial for emerging therapies specific to a particular genetic mutation, or for treatments with approved gene therapies that are coming down the line.

For full information about genetic testing and IRDs, please see our Genetic Testing Toolkit “Sending a Red Alert!

For more information on inheritance patterns of IRDs, please see http://www.retina-international.org/patients/your-eyes/inheritance-patterns

Coping with a diagnosis

 

Loss of vision can happen suddenly or can be gradual as part of a long-term health issue. Regardless of the onset, it can be life-altering. The thought of losing one of our most valuable senses can cause feelings of fear for ourselves, for our families and uncertainty for the future. However, supports for the affected person and for their families can help with the transition to a new lifestyle.

Diagnosis

The time of diagnosis can be difficult and many different emotions can arise. For some people, it may be quite distressing, upsetting or overwhelming. People often struggle to understand how this has happened and how they will cope now and in the future. If you feel like this, you are not alone. There is no need to feel guilty about these feelings. It is important to find support for your situation and to have a way to express your feelings and thoughts. The initial feelings that people experience after a diagnosis can include shock, denial and despair. These feelings will lessen as time passes. While it is natural to feel like this after such a life-changing diagnosis, it could help you to talk to a healthcare professional or a counsellor.

At such a challenging time, engaging in psychotherapy can help. Working with a psychotherapist in a safe, trusting and non-judgemental environment allows the individual with sight loss the time and space to make sense of what is actually happening to them, away from the pressure of well-meaning, but often ill-informed and anxious, family and friends. With the appropriate support and guidance it is possible to work through and overcome difficulties to find new and life-enhancing meaning and purpose in living.

The National Eye Institute/National Institutes of Health (NEI/NIH) have some useful videos, including this one ‘How Can People With Low Vision Maintain a Positive Outlook?

Identity

The changes that a person with sight loss may encounter can be practical and psychological. Some people may have issues with their sense of identity, as they transition from a sighted to a partially or non-sighted lifestyle. This is very common and many people find it difficult at first. Adapting to the new way of living is unique for each person and this uniqueness should be respected by all who offer assistance. The transition can be aided by supports to help adjust to the new way of life and if necessary, to rebuild confidence and increase independence. People make this transition every day and continue to enjoy life with new or adapted careers, new or rediscovered hobbies.

Relationships

Sight loss can also affect the people in the individual’s life including partner, children, parents, extended family and friends. These effects can vary given an individual’s circumstances, for example the effects on a family when a young child is diagnosed can be different from those surrounding a teenager or young adult, and different again from when an adult is diagnosed. It is natural for the people in your life to go through a range of emotions and concerns too. Adults may be concerned by the relationship with their partner, with fears that they may become dependent on their partner. It is advisable for couples to talk to each other about things that the visually impaired person can do themselves and what areas they would like support with. Helping needn’t result in taking away independence. Sight loss may change and this may determine how much assistance or support is needed. Being a parent with sight loss can add challenges to your relationship with your children. However, while you may need to make adjustments there is no reason for your diagnosis to stop you from parenting your child. Talking to children about your sight loss can help them understand what you can see and how it affects you. While children and grandchildren will want to help you, it is advisable to try to be as independent as possible for as long as you can.

The NEI/NIH have some very informative videos on low vision, like this one ‘How Can Family Members Help a Loved One With Low Vision?

For parents

If your child has been diagnosed with a visual impairment, it is important to remember that, despite the diagnosis, your child has not changed. Your child is a person that is much more than the threat of blindness. Children are more aware of things than we give them credit for, and so it is important to be honest and answer their questions truthfully and compassionately. Ideally, a child should be told about their diagnosis in an age-appropriate way by a loving person who is close to them. If a child isn’t told about their diagnosis but then discovers information from sources other than the family, for example overhearing a doctor’s conversation, over time this can foster mistrust and resentment. However, there are many supports and outside help available to parents, so that they don’t have to do everything alone. Parents can often feel that they must be the sole doctor and carer and nurse for their child. However, this can be an overwhelming and impossible task. Outside help can support those roles to allow parents to do the very important role of being parents to their child.

What is in your area?

While it is helpful to talk to family and friends about your situation, it might also be helpful to talk to people who have had similar experiences to you. They might have an understanding of what you are going through that your family or friend may not. Your local sight loss charity can connect you with such people in your area. Your partner, family and friends can also find support at your local sight loss charity. You can also find information about activities or events that are available for people with sight loss in your area. They can help you with information and advice on getting the help and support that you need, including accessing emotional support, counseling, vision rehabilitation supports and information on services within your community.

Please see the member charities of Retina International for a local sight loss charity near you http://www.retina-international.org/our-members

For helpful information on ‘What is low vision?’ please see this video from the NEI/NIH

Coping with more than loss of sight

Sometimes, people with sight loss can experience other issues. For some, it can be that their sight loss is part of a syndrome and so is just one of their health issues. For information on some syndromes that include vision loss, please see our section on ‘What are IRDs’ and ‘FocusOn: Usher Syndrome’.

Some people with sight loss can experience visual hallucinations, or see things that are not there. This can be very frightening for people and some fear that they are having mental health problems. However, it is a common condition in people who have recently lost their sight where the brain is adjusting to the loss of visual information. It is called Charles Bonnet syndrome and while it can be distressing, the hallucinations can get less frequent as time passes.

Vision Rehabilitation

Vision rehabilitation is one of the supports that ensure you have the right information, training, skills and aids to transition to living with sight loss. Your local sight loss charity will have information on local supports.

Visual rehabilitation can help you achieve your personal goals that can be identified by a support assessment. Vision rehabilitation support can be quite varied. It can include helping you understand your eye disease and what it means for you, understand the changes you may need to make in your life, how to continue looking after yourself and finding new ways to do tasks. It can include ensuring you are safe inside your home and how to care for it: for example, assessing mobility needs, reducing risk of falls and advice on appropriate equipment or mobility aids, if needed. Simple adjustments such as reviewing the lighting in your home can make helpful improvements. A low vision service can advise you on the use of aids such as magnifiers and specialist lighting.

Being able to get out and about is very important to maintain independence. Vision rehabilitation can help with travelling confidently and safely and give advice on using public transport. Vision rehabilitation support is not just for physical adjustments but also takes into account a person’s communication needs and how they keep in touch with others. This can be aided with help with reading, writing, talking books and newspapers, telling the time, using technology such as smartphones, tablets and speech software. Most smartphones or computers have accessible features built in while there are many packages available that enable everyone to use a computer. ViaOpta is a recently developed suite of mobile applications to assist visually impaired people with their daily lives. These apps allow individuals to maintain their independence by assisting with daily activities, navigating their local region and recognising people and places using image analysis technology. See https://www.viaopta-apps.com for more details.

There are many options for support, however it is best not to assume the first solution will be right for you. We’re all different and have different needs.

A visual impairment does not preclude an individual from education or employment. Appropriate vision rehabilitation can ensure access to training, education and learning opportunities as well as advice about disability employment.

The NEI/NIH has useful videos, including this one on ‘How Can People With Low Vision Maintain Their Independence?’

And this NEI/NIH video describing ways that can help with vision loss on a day to day basis ‘What Can I Do if I Have Low Vision?’

With the appropriate support and guidance, it is possible to work through and overcome difficulties to find new and life-enhancing meaning and purpose in living.

Incidence and Prevalence

Incidence and prevalence are commonly used terms when talking about how frequently a disease occurs, however they convey different information. Prevalence is the proportion of cases in the population at a given time rather than rate of occurrence of new (or newly diagnosed cases) within a specified period of time. Therefore, incidence conveys information about the risk of contracting the disease, whereas prevalence indicates how widespread the disease is.

Inherited retinal diseases (IRDs) are the leading cause of vision loss in people of working age (16 to 64 years) and are estimated to affect 1 in every 3000 people. Taking into account all the different forms of Retinitis pigmentosa among the general population, the overall prevalence is variably reported as 1 case in 2500 to 1 case in 7000 persons. The prevalence of Leber congenital amaurosis (LCA) is estimated as 1 in 50,000 to 1 in100,000 people. Overall, LCA accounts for 5% of all retinal dystrophies and 20% of blindness in school age children. The prevalence of Usher syndrome has been reported to range from 3.2 to 6.2 cases per 100,000 people. Usher syndrome was estimated to be responsible for 3%-6% of all childhood deafness and approximately 50% of all deaf-blindness.

The prevalence of Stargardt disease was estimated to be between 1 in 8000 and 1 in 10,000. The prevalence of choroideremia is estimated to be 1 in 50,000 to 100,000 people. However, it is likely that this condition is underdiagnosed because of its similarities to other eye disorders. Choroideremia is thought to account for approximately 4 percent of all blindness. The exact prevalence of retinoschisis is currently unknown, but it is thought to affect between one in 5,000 to 20,000 people. Leber Hereditary Optic Neuropathy (LHON) affects approximately 1 in 50,000 people. The prevalence of Cone-rod dystrophy is estimated at 1 in 40,000.

Taking Care of your eyes

 

Care 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.

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

Health Care Professionals that care for your eyes

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 to visit will depend upon your symptoms and your location (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 4 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 disorder

An orthoptist

An allied health professional involved in the assessment, diagnosis, and management of disorders of the eyes, extra-ocular muscles and vision. Orthoptists are an important part of the eye care team and work in close association with ophthalmologists, usually in a hospital based setting. They are involved in many areas of care, including paediatrics, neurology, community services, rehabilitation, geriatrics, neonatology and ophthalmic technology.

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, so 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 to Ask your Doctor

You may feel overwhelmed by the information you receive at your appointment so it can be useful to make a list of questions beforehand to take with you. Here are some suggestions that might be helpful:

Q: What is my diagnosis?

Q: How will my vision be affected?

A doctor will not be able to give you an exact answer to this question, as everyone is different, and conditions can progress at different rates in different people. They will be able to tell you which parts of your vision are most likely to be affected, for example, your central vision or peripheral vision.

Q: How will it affect my home and work life?

The doctor may be able to give you an example of how the condition will affect an everyday task such as reading or driving.

Q: What is the short-term and long-term prognosis for my disease or condition?

Many conditions will cause your vision to change over time. A doctor will not be able to give you an exact prognosis or time line but may able to give you an idea of what can happen in the short- and long-term in most cases of your condition.

Q: What caused the disease or condition?

Is your condition genetic or can it be affected by lifestyle or environmental factors.

Q: Are there local agencies or organisations that can help me learn more about my condition and vision loss?

There may be an organisation or support group that deals specifically with your condition or may be able to give you more information.

Q: Has my vision changed since my last visit?

Q: Could medication or health supplements I take have any effect on my vision?

If this is something you are unsure about, bring a list of any medications or supplements to your appointment and ask your doctor about them.

What Happens at Your Ophthalmology Appointment?

When you visit your ophthalmologist, you will be asked to perform a number of tests that measure different parts of your vision and look at different parts of your eyes. Some of the tests are very quick and straightforward while others will take more time as they require drops in your eyes to take effect before they can be performed. Some of the tests require you to look at something and respond about what you see. Your ability to perform these tests will depend on your level of vision, and some people may find them difficult or frustrating. Other tests involve the measurement of involuntary responses of the eye or taking photographs of the eye. Some of the tests that are used are explained below. If you have any questions about any of the tests or are unsure of anything taking place during your appointment, don’t be afraid to ask your ophthalmologist or test technician to explain it you.

Visual Acuity Testing

Most people are familiar with visual acuity testing, which involves reading letters from a chart while sitting or standing a certain distance away. The purpose of this test is to measure your central vision which is the ability to see fine detail.

Colour Testing

This test measures your colour perception. You will be asked to look at a series of images composed of many small circles. Someone with normal colour vision can recognise numbers within the images.

Visual Field Testing

This test measures the scope or range of vision, including peripheral (side) vision and central vision. A light is brought in from the side on a screen, and slowly moved to the centre of vision. You are asked to press a button as soon as you see the light.

Electroretinogram (ERG)

This measures the electrical response of the light-sensitive cells in the eye, the rods and cones. It also measures retinal function. Prior to this test, you will be given drops in your eyes to dilate the pupils. You will also be given an anaesthetic eye drop to numb your eyes. A special type of recording contact lens will then be placed over your eye and electrodes will be placed on the skin near the eye. You will be asked to watch some flashing lights; these are used to stimulate the retina.

The electrodes measure the electrical response of the retina to the flashing lights. The test will be performed first in a dark room and then again when the lights are turned on. The test does not cause any pain, but some people may find it uncomfortable. Because of the drops used, you may notice that your vision is blurred for quite some time afterwards.

Fundus Photographs

This test takes a photograph of the retina fundus at the back of the eye using a special camera. The images will show any changes or abnormalities in the back of the eye. You will be given drops to dilate your eyes before this test.

Fluorescein Angiogram

During this test a special dye, called fluorescein, is injected into the bloodstream. The dye is injected through the arm. Its purpose is to highlight the blood vessels in the back of the eye so they can be photographed. This makes it easier for a doctor to see abnormalities in the back of the eye.

If you have any questions about anything that happens at your appointment or are unsure about any of the information you receive, don’t be afraid to ask your ophthalmologist or test technician to explain it you.