Contents

1.1 Definitions: vision impairment and blindness
1.2 Conditions leading to vision impairment and blindness

Summary

Vision impairment is broadly defined as a limitation in one or more functions of the eye or vision system. This study uses the following definitions:

• blindness – best-corrected visual acuity of less than 6/60 in the better-seeing eye;
• moderate vision impairment – best-corrected visual acuity of less than 6/18 but better than or equal to 6/60 in the better-seeing eye;
• mild vision impairment – best-corrected visual acuity of less than 6/12 but better than or equal to 6/18 in the better-seeing eye.

A range of eye conditions can lead to vision impairment and blindness. This study presents the total prevalence rates of mild/moderate vision impairment and blindness, and the proportions of vision impairment and blindness primarily due to cataracts, glaucoma, age-related macular degeneration, diabetic retinopathy and other causes.

Low vision and blindness are prevalent within populations worldwide. In the Republic of Ireland (ROI), the prevalence of blindness alone in 2003 was estimated to be 227 cases per 100,000 adults based on NCBI register data (Kelliher et al, 2006). Accounting for unregistered cases of blindness and less severe vision impairment (VI), the prevalence of vision loss is expected to be far greater. Vision loss imposes a major personal impact on people’s daily lives, but there are also major economic impacts on individuals, families, support agencies, society and the state (Jackson et al, 2008).

Deloitte Access Economics was commissioned by the NCBI (National Council for the Blind of Ireland) to estimate the economic impact of VI and blindness in the ROI in 2010, including health system costs, other financial costs, and the loss of wellbeing. This study also includes future projections of VI in the ROI to the year 2020, and cost effectiveness analyses for three eye care interventions that could be used to manage the prevalence and cost of vision loss in the ROI.

Deloitte Access Economics has previously conducted several country-specific burden of disease studies for VI in Australia, Canada, Japan, UK and US (Access Economics, 2004; 2006; 2008a; 2008b; 2009; 2010a), as well as a study on the global economic impact of VI (Access Economics, 2010b). This is the first study to comprehensively estimate the economic impact of VI in the ROI. The methodology employed is Deloitte Access Economics’ robust disease cost-burden analysis (DCBA) framework, which has been considered a best practice approach for measuring the full cost of VI (Frick et al, 2010).

This report is structured as follows.

• Chapter 2 estimates the prevalence of VI and blindness in 2010 by age, gender and cause and includes projections for the years 2015 and 2020.
• Chapter 3 presents the direct health care system costs of VI in the ROI.
• Chapter 4 calculates the indirect financial costs of VI including productivity losses, costs of informal care, and deadweight welfare loss.
• Chapter 5 estimates the burden of disease from VI which is the intangible loss of wellbeing, measured in disability-adjusted life years (DALYs), and disaggregated by healthy years of life lost due to disability (YLD) and years of life lost due to premature death (YLL).
• Chapter 6 summarises the total economic cost of VI in the ROI in 2010 disaggregated by cost component.
• Chapter 7 presents the cost effectiveness analyses for three eye care interventions: screening for people with diabetes; screening for the elderly; and reducing cataract surgery waiting lists.

1.1 Definitions: vision impairment and blindness

VI can broadly be defined as a limitation in one or more sensory functions of the eye or vision system. The quantification of VI commonly involves an assessment of visual acuity (VA/high contrast spatial resolution), contrast sensitivity (CS/low contrast spatial resolution), visual field (VF/peripheral vision), and colour vision (CV/colour discrimination). Colour blindness, which is usually a genetically determined inability to distinguish differences in hue, is not a subject of this report.

VA is, in fact, a measure of the finest spatial detail that the visual system can resolve. It is usually measured using letter or symbol charts (optotypes) presented at test distances of 4-6 metres. The term ‘distance visual acuity’ implies that the measurement has been obtained after any refractive abnormality has been corrected. The term ‘vision’, when used to express resolution, should be restricted to situations when measurements are made without any optical correction in place. Additional terms in the literature include ‘best corrected visual acuity’ (BCVA), which indicates the system’s optimal acuity with best correction; and ‘habitual visual acuity’ or ‘presenting visual acuity’ which refer to the VA measured using current spectacles or contact lenses. When expressing the ability of the eye or visual system to resolve high contrast detail at near or intermediate distances, the measurement is usually expressed as the actual size of the smallest symbol (letter) resolvable at a specified working distance. Letter size is, however, often expressed in printer’s font size rather than millimetres or inches.

Contrast sensitivity differs from acuity in that it is not a single measure but a series of measurements designed to show how the eye detects fading detail at different spatial frequencies (acuity levels). Interestingly, the visual system’s optimal contrast detection threshold is for large letters similar in size to the largest letter on a conventional Snellen chart. Contrast sensitivity is usually measured using letter or grating charts and is most accurately depicted in graphical form.

Vision, or VA, is usually expressed as a fraction – 6/6 (UK), 20/20 (US) – decimal 1.0 (European), or in a logarithmic series (0.0). In the fraction form the numerator (upper number) represents the test distance whereas the denominator (lower number) represents the distance at which the smallest letter detectable subtends an angle of 5 minutes of arc at the eye. When expressed in decimal or logarithmic form it is important to note the test distance. A figure of 6/12, for example, would indicate that an individual can clearly see the high contrast detail within a target at a distance of six metres, that a person with unimpaired vision could see at a distance of twelve metres.

Visual fields are expressed in terms of the distance from point of fixation, measured in degrees along an arc, to the last point in the peripheral field that is just detectable. Diagnostic visual field tests usually assess retinal sensitivity using tiny flashing (static) targets presented randomly in the peripheral field as the patient fixates a central target.

Since VI and blindness can vary between one eye and the other, prevalence rates can be reported for either the better or the worse eye in terms of the extent of sight loss. Although sight loss may be asymmetrical, often it is only when sight loss becomes bilateral that it is identified and treated. When reporting prevalence rates, better eye measures provide conservative estimates of sight loss while worse eye measures may tend to overstate sight loss and costs. In this study, the conservative approach of reporting VI for the better eye has been adopted.

BCVA refers to a VA measurement with the best glasses or contact lens prescription for that person. On the other hand, presenting VA refers to VA that is unaided, or with spectacles, if worn. The major difference between the two measurements occurs with uncorrected (or under-corrected) refractive error as best-corrected measurements do not include the population with this condition. This study uses the best-corrected measure for VI definitions, as this was the best approach permitted by available prevalence data.

In this study, VI excluding blindness is disaggregated into mild and moderate VI. The definitions of VA for mild VI, moderate VI, and blindness are consistent with previous Deloitte Access Economics reports and are commonly used in North America, Australia, and most of Europe:

• blindness is defined as BCVA less than 6/60 in the better-seeing eye;
• moderate VI is defined as BCVA less than 6/18 but better than or equal to 6/60 in the better-seeing eye; and
• mild VI is defined as BCVA less than 6/12 but better than or equal to 6/18 in the better-seeing eye.

These definitions differ from those used by the World Health Organisation (WHO), which defines VI as BCVA <6/18 and blindness as BCVA <3/60. The WHO definitions align with International statistical classification of diseases, injuries and causes of death 10th revision (ICD-10) classifications.

The current definition of blindness in the ROI is VA corrected with glasses of less than 6/60 (0.1 decimal/1.0 logMAR) in the better eye, or a field of vision limited to a widest diameter of vision subtending an angle of not more than 20 degrees (NCBI).

In assessing the burden of VI in Ireland, it is important to include people with a VA between 6/12 and 6/18 since their quality of life will also be impacted by VI. Deloitte Access Economics has previously demonstrated increased health care costs and mortality for people with mild VI (for example see Access Economics, 2010). Furthermore, mild VI is associated with a disability burden, albeit relatively low (Mathers et al, 1999). Dandona and Dandona (2006) have recommended adding this mild VI category to ICD definitions. They argue that in more developed countries this level of vision is considered necessary for daily tasks and is already used to define VI, while the increasing complexity of daily tasks in less developed countries will require better vision over time.

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1.2 Conditions leading to vision impairment and blindness

There are a range of eye conditions that can lead to VI and blindness. This study presents VI prevalence for Ireland disaggregated by:

• cataracts;
• glaucoma;
• age-related macular degeneration (AMD);
• diabetic retinopathy (DR);
• other causes.

This report presents the cost effectiveness of three interventions to address the burden of VI in the ROI, specifically relating to these conditions including reduced waiting lists for cataract surgery, vision screening for the elderly, and vision screening for people with diabetes (the elderly and people with diabetes are two groups at higher risk of VI and blindness).

More detail is presented below for these four causes of VI.

1.2.1 Cataracts

A cataract is a cloudy area in the eye’s lens. The lens is made mostly of water and protein, with the protein arranged to let light pass through and focus on the retina. Some of the protein may clump together and cloud a small area of the lens. Over time, the cataract may grow larger and cloud more of the lens, making it hard to see.

The most common symptoms of cataract are cloudy or blurry vision; problems with light – headlights that seem too bright, glare from lamps or the sun, or a halo or haze around lights; colours that seem faded; double or multiple vision (this symptom goes away as the cataract grows); and /or frequent changes required in eyeglasses or contact lenses.

There are four main types of cataract:

• Age-related cataract: Most cataracts are related to ageing.
• Congenital cataract: Some babies are born with cataracts or develop them in childhood, often in both eyes.
• Secondary cataract: Cataracts may be linked to certain other health issues, such as diabetes or steroid use.
• Traumatic cataract: Cataracts can develop soon after an eye injury, or years later.

It is still unclear what causes cataract, however age, smoking, diabetes, use of cortico-steroids and ultraviolet exposure increase the risk. Detection is through an eye examination including a VA test (eye chart test), pupil dilation (where the pupil is widened with eye-drops to allow the eye care professional to see more of the lens and look for other eye problems).

For an early cataract, different spectacles, magnifying lenses, or stronger lighting may improve vision. At a certain point, based on VA and patient concern, surgery may be needed to improve vision.

1.2.2 Age-related macular degeneration

AMD usually develops after 50 years of age, progressively destroying the macula, the central portion of the retina and impairing central vision. Changes to the central area of the macula responsible for detailed vision can be rapid, impacting severely on day to day life.

In the early stages of AMD, pale yellow spots caused by distinct lesions consisting of lipids and protein (known as drusen) accumulate as deposits within Bruch’s membrane and beneath the retinal pigment epithelium. The progression of ‘early’ AMD to ‘late’ AMD, is often from dry AMD to wet AMD, and is generally associated with decreasing VA.

Geographic atrophic (GA) AMD is characterised by light-sensitive cells in the macula slowly breaking down and being replaced with scar tissue. People with GA AMD have extensive medium-sized drusen or one or more large drusen in one or both eyes. At this stage, people with GA AMD will have substantially decreased capacity for near visual tasks as central vision deteriorates.

Wet AMD is caused by blood vessels reproducing in the choroid in a process called choroidal neovascularisation. The new choroidal vessels leak or bleed into the underlying retina, damaging the retina, including the central macula region. The blood and fluid can also cause macular scarring or the detachment of either the retinal pigment epithelium or sensory retina. Wet AMD is characterised by the appearance of central visual blurring and distortion, with straight lines appearing crooked or wavy. It can occur in one eye without any symptoms being recognised by the person, although symptoms become more noticeable once the second eye is affected.

Several risk factors can increase the risk of developing AMD and the speed at which the disease progresses. Cigarette smoking is the main lifestyle risk factor, although alcohol consumption and obesity have also been associated with an increased risk of developing AMD. Control of these modifiable risk factors could reduce the risk of developing AMD by 45% (Tomany et al 2004).

Progression of AMD will also occur more steadily if protective measures are taken. Nutrition, or more specifically dietary antioxidants, plays an important role in the occurrence, prevention and treatment of AMD. Recent research suggests that some foods may decrease a person’s risk for the disease by up to 65% (Tan et al, 2008). Since there is currently no effective treatment for GA AMD, prevention is the first approach to reducing VI. Treatments available for wet AMD include laser treatment, photodynamic therapy, and recent injectable medications including ranibizumab.

1.2.3 Diabetic retinopathy

DR is an important cause of VI. It occurs when diabetes mellitus (DM) damages the tiny blood vessels inside the retina, and usually affects both eyes. At first, micro-aneurysms occur. As the disease progresses, some blood vessels that nourish the retina are blocked. There are two ways that VI occurs:

• proliferative retinopathy: if many blood vessels are blocked, and several areas of the retina are deprived of their blood supply, signals are sent to grow new blood vessels, which may be abnormal and fragile, growing along the retina and along the surface of the clear, vitreous gel that fills the inside of the eye. These blood vessels have thin, fragile walls that, if they leak blood into the centre of the eye, can result in blurred vision and blindness.
• macular oedema: fluid can leak into the macula, causing swelling and blurred vision. This is more likely to occur as the disease progresses. About half of people with proliferative retinopathy also have macular oedema.

All people with type 1 or type 2 DM are at risk of developing DR and should have a comprehensive dilated eye examination at the time of diagnosis and at least once every two years thereafter if no DR is found (NHMRC, 2008). If DR is detected, further examinations should be conducted annually or at three-12 monthly intervals depending on the level of DR. Any visual symptoms should prompt a further referral (NHMRC, 2008). Early diagnosis and treatment can prevent up to 98% of severe VI (Access Economics 2010a). Lack of awareness and communication breakdowns are major impediments to regular screening.

DR often has no early symptoms. If bleeding occurs, the person can see specks of blood, or spots, “floating” in their vision. Occasionally spots clear without treatment, but haemorrhages tend to happen more than once, often during sleep. The earlier treatment is received, the more likely it is to be effective. Control of blood sugar, cholesterol and blood pressure, as well as the length of time a person has had diabetes are related to the risk and severity of DR.

1.2.4 Glaucoma

Glaucoma is a group of diseases that can lead to damage to the eye’s optic nerve and result in blindness. It has no symptoms at first, but once detected and with early treatment, eyes may be protected against serious VI and blindness.

The optic nerve comprises over a million nerve fibres connecting the retina with the brain. In the front of the eye is a space called the anterior chamber – clear fluid flows in and out of this space, leaving the chamber at the angle where the cornea and iris meet. When the fluid reaches the angle, it flows through a spongy meshwork, like a drain, and leaves the eye.

Open-angle glaucoma, the most common type, occurs when, for unknown reasons, the fluid passes too slowly through the meshwork drain. As the fluid builds up, the pressure inside the eye rises. Unless the pressure at the front of the eye is controlled, it can damage the optic nerve and cause VI. At first, vision is normal and there is no pain. Without treatment, side vision is reduced, and the remaining forward vision may decrease until there is no vision left.

Increased risk for glaucoma occurs with elevated intraocular pressure, older age, large cup to disc ratio, thin central cornea, family history and ethnicity (particularly people from African-American descent).

Glaucoma is detected through an eye examination including visual acuity, visual field, tonometry and optic nerve examination. Although there is no cure for glaucoma, early diagnosis and treatment are important to control it and thus protect sight.

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