Definitions

2030 In Sight is the global strategy to end avoidable sight loss by 2030. It calls for action in three key areas: elevating vision as a social and economic development issue, integrating eye health into wider health systems, and activating public and market demand for eye care.

Built on the WHO World Report on Vision, the Lancet Global Health Commission, and the UN resolution Vision for Everyone, the strategy guides global efforts to ensure everyone has access to the eye care they need by 2030.

ARMD is a disease affecting the central area of the retina (macula) at the back of the eye.

AOP is an umbrella term often used to describe eye care workers in levels 2 and 3 of the Eye Care Competency Framework (ECCF).

Level 2 roles involve 3–12 months of training beyond high school and include positions like refractionists, spectacle dispensers, and vision technicians. These workers operate under the guidance of more highly trained eye care professionals.

Level 3 roles require 1–4 years of tertiary education and include occupations such as ophthalmic assistants, specialist nurses, orthoptists, and optical dispensers. They provide more advanced clinical support, often under the supervision of ophthalmologists or optometrists.

Age-standardised prevalence adjusts for differences in population age structures that exists between countries, as it tells us what the rates of sight loss would be if each country had identical age structures.

Age-standardisation can be useful for comparing rates of sight loss between females and males, as we can see what the rates would be if there were equal men and women in each country/region. Age-standardisation can also be useful when comparing trends over time, without the confounding effects of population structure changes.

Astigmatism is usually caused by an irregularly shaped cornea, which prevents light from focusing at a single point on the retina. As a result, both distance and near objects appear blurred and distorted.

The opacification (clouding) of the lens of the eye, which prevents clear vision and usually progresses to blindness if left untreated.

Congenital disorders are also known as congenital abnormalities, congenital malformations or birth defects. They can be defined as structural or functional anomalies (for example, metabolic disorders) that occur during intrauterine life and can be identified prenatally, at birth, or sometimes may only be detected later in infancy, such as hearing defects. Broadly, congenital refers to the existence at or before birth.

Corneal visual impairment encompasses a wide variety of infectious, degenerative, and inflammatory eye diseases that cause scarring of the cornea, the clear window positioned at the front of the eye.

The CSR is the number of cataract operations performed per year per one million population.

Diabetic retinopathy is caused by diabetes damaging the small blood vessels in the retina at the back of the eye. It usually affects both eyes and can lead to vision loss if left untreated. Poorly controlled blood sugar is the main risk factor, while high blood pressure and high cholesterol can further increase the risk and severity.

eCSC is defined as the proportion of adults aged 50 years and older who are in need of cataract surgery, who have received this surgery, and have a resultant good-quality distance visual acuity outcome.

eREC is defined as the proportion of people in need of refractive error services who have received services (i.e. spectacles, contact lenses, or refractive surgery) and have a resultant good-quality outcome.

The ECSAT tool provides guidance for assessing the status and functionality of a country’s eye care service based on the six areas of the WHO framework for strengthening health systems.

Universal Eye Health: a Global Action Plan 2014–2019 (GAP) was a strategy adopted by the World Health Assembly in 2013 to help countries reduce avoidable blindness and visual impairment and improve access to rehabilitation for people with vision loss. It called for better coordination between governments, WHO, and international partners, and encouraged countries to focus resources on the most cost-effective eye care services. The plan supported the use of data, innovation, and stronger health systems to prevent and treat eye diseases, especially in areas where services are limited. 

The GBD Study is the most comprehensive world-wide observational epidemiological study to date. It describes mortality and morbidity from major diseases, injuries and risk factors to health at global, national and regional levels.

GDP at purchaser’s prices is the total value of all goods and services produced in a country, including taxes on products and excluding subsidies. It doesn’t subtract depreciation or the depletion and degradation of natural resources.

GNI shows the average income per person in a country, measured in international dollars using purchasing power parity (PPP) to account for price differences between countries.

Gross national income (GNI) includes the value of all goods and services produced by residents, plus taxes (minus subsidies) on products, and income received from abroad. PPP adjusts for cost of living differences so incomes can be compared fairly across countries.

A composite measure reflecting inequality in achievement between women and men in three dimensions: reproductive health, empowerment and the labour market.

Glaucoma refers to a group of eye conditions that all involve damage to the optic nerve, usually with a characteristic pattern of vision loss. This damage is caused by the death of retinal ganglion cells and often appears as cupping of the optic nerve and arcuate loss in the mid-peripheral visual field.

A summary measure of average achievement in key dimensions of human development: a long and healthy life, being knowledgeable and have a decent standard of living.

A refractive error where light from distant objects is focussed behind the retina, when the person is not accommodating. This can make it difficult to see near objects, whilst for adults both near and distance vision may be affected.

IHDI is the HDI value adjusted for inequalities in the three basic dimensions of human development.

The inequality-adjusted life expectancy index is the HDI life expectancy score modified to reflect inequality in how long people live, using data from life tables.

Services that are managed and delivered so that people receive a continuum of eye health interventions covering promotion, prevention, treatment and rehabilitation.

Light from distant objects is focussed in front of the retina, making it difficult to clearly see objects in the distance. Myopia is usually due to an excessive elongation of the eye.

A vision-threatening condition in people with myopia, usually high myopia, which comprises diffuse, patchy macular atrophy with or without lacquer cracks, choroidal neovascularization and Fuchs spot.

A group of key stakeholder representatives, with responsibility for the development and implementation of national eye health plans.

The government appointed person responsible for coordination and implementation of national eye health activities.

A strategic document that guides the Ministry of Health and other stakeholders in their efforts to reduce avoidable blindness and vision impairments.

Onchocerciasis, commonly known as river blindness, is a parasitic disease caused by the filarial nematode Onchocerca volvulus, transmitted to humans through the bites of infected blackflies of the genus Simulium.

Ophthalmologists are medical eye specialists classified at Level 5 of the Eye Care Competency Framework (ECCF).

They typically complete 7 or more years of higher education, including a medical degree and specialisation in ophthalmology. They work independently in hospitals or specialist clinics, diagnosing and treating eye conditions, performing surgery, and providing rehabilitative care. Many also contribute to teaching and research.

Optometrists are primary eye care providers classified at Level 4 of the Eye Care Competency Framework (ECCF).

They usually complete 4–7 years of university education. Optometrists work independently in various settings to provide eye and vision care, including diagnosing and managing vision problems, certain eye conditions, and the rehabilitation of the visual system. They may also take on academic, teaching, or research roles.

In a younger eye, the lens is elastic and can change shape as the ciliary muscles supporting the lens contract or relax, enabling images of near objects to be focussed on the retina. This is known as accommodation, but as part of the ageing process the lens becomes harder and less elastic, making accommodation more difficult. Most people over the age of 40 will have a degree of presbyopia which can make it difficult to see near objects clearly without optical correction.

Age-standardisation tells us what the rates of sight loss would be if each country had identical age structures. Age-standardised rates are useful when comparing countries or regions.

The crude prevalence of sight loss is the percentage of the population affected by sight loss. Crude prevalence allows you to see where there are higher or lower proportions of people living with sight loss, but it doesn’t account for differences in population structures, such as age.

Refractive disorders refer to myopia, hyperopia and astigmatism that can cause blurred distance and/or near vision if not corrected with spectacles, contact lenses or laser surgery.

RAAB is a rapid, population-based survey methodology on blindness, visual impairment and eye care services among people aged 50 years and over.

An umbrella term covering all forms of reduced vision, vision impairment and blindness, regardless of severity or whether it affects distance or near vision.

The SDGs were adopted by the UN General Assembly in September 2015. They include 17 Goals and 169 targets to bring about change in all countries and globally to end poverty, protect the planet and ensure prosperity. They integrate all three dimensions of sustainable development – the economic, social and environmental – and are built on a commitment to leave no-one behind.

Trachoma is an infectious eye disease caused by the bacterium Chlamydia trachomatis. It spreads through contact with eye or nose discharge from infected individuals, especially in areas with poor sanitation and limited access to clean water. Repeated infections lead to scarring of the inner eyelid, which can cause the eyelashes to turn inward (trichiasis), scraping the cornea and potentially leading to blindness.

Trachoma is the leading infectious cause of blindness worldwide, but it is preventable and can be eliminated through the WHO-recommended SAFE strategy: Surgery, Antibiotics, Facial cleanliness, and Environmental improvement.

Universal health coverage (UHC) means that all people have access to the full range of quality health services they need, when and where they need them, without financial hardship. It covers the full continuum of essential health services, from health promotion to prevention, treatment, rehabilitation and palliative care.

The International Classification of Diseases 11th Revision (2025) classification for distance vision impairment is as follows.

– Mild vision impairment: Visual acuity is worse than 6/12, 20/40, or 0.5, but equal to or better than 6/18, 20/70, or 0.3.
– Moderate vision impairment: Visual acuity is worse than 6/18, 20/70, or 0.3, but equal to or better than 6/60, 20/200, or 0.1.
– Severe vision impairment: Visual acuity is worse than 6/60, 20/200, or 0.1, but equal to or better than 3/60, 20/400, or 0.05.
– Blindness: Visual acuity is worse than 3/60, 20/400, or 0.05.

Moderate to severe visual Impairment (MSVI) encompasses both the moderate and severe visual impairment categories.

If the extent of the visual field is taken into account, patients with a visual field of the better eye no greater than 10° in radius around central fixation are considered to be blind.

The International Classification of Diseases 11th Revision (2025) classifies near vision impairment as presenting near visual acuity worse than N6 at 40cm with existing correction.

VLEG is an international group of mainly ophthalmologists and optometrists with experience in ophthalmic epidemiology. VLEG provides global technical leadership in the development and improvement of epidemiological estimates for blindness and vision impairment.

The World Health Assembly is the decision-making body of the World Health Organization (WHO). It is attended by delegations from all WHO Member States and meets annually to set global health policies, review progress, and decide on the organisation’s priorities and budgets.