Glossary

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Aniridia

A rare congenital eye condition involving the partial or complete absence of the iris, often accompanied by reduced visual acuity, light sensitivity (photophobia), nystagmus, and sometimes glaucoma or cataracts. Digital accommodations typically include high screen brightness…

Blue Cone Monochromatism(also: BCM, S-cone Monochromacy)

A rare inherited vision condition in which only the blue (short-wavelength) cones function, resulting in severely reduced color vision, reduced visual acuity, photophobia, and nystagmus. Affected individuals see the world in shades of blue and yellow and typically benefit from…

Cataracts(also: Cataract)

A clouding of the eye's natural lens that causes blurry or hazy vision and increased sensitivity to glare. Cataracts are the leading cause of vision impairment worldwide and become increasingly common with age. People with cataracts may experience difficulty reading, reduced…

Category 3 Blindness(also: ICD-10 H54 Category 3, WHO Category 3 Visual Impairment)

A classification of severe visual impairment under the World Health Organization's ICD-10 coding for disorders of the visual system (H54). Category 3 covers blindness in which the better eye has presenting visual acuity worse than 1/60 (20/1200 Snellen) but can still perceive…

Hyperopia(also: Farsightedness, Long-Sightedness, Hypermetropia)

A refractive error in which the eye focuses light behind the retina rather than on it, causing near objects to appear blurred while distant objects may remain relatively clear. Hyperopia occurs when the eyeball is too short or the cornea is insufficiently curved. It is…

Keratoconus

A progressive eye condition in which the normally round cornea thins and bulges into a cone-like shape, causing irregular astigmatism and significant visual distortion that cannot be fully corrected with standard glasses or contact lenses. Keratoconus typically begins in…

Myopia(also: Nearsightedness, Short-Sightedness)

A common refractive error in which the eye focuses light in front of the retina rather than on it, causing distant objects to appear blurred while near objects remain clear. Myopia occurs when the eyeball is too long or the cornea is too curved, and affects an estimated 30% of…

Near Visual Acuity(also: NVA, Near Acuity)

A measure of the eye's ability to resolve fine detail at a close distance, typically tested at 40 centimetres. Near visual acuity is particularly important for tasks involving reading, handheld device use, and close-up work. It is commonly measured using Snellen notation (e.g.,…

Optic atrophy(also: Optic nerve atrophy)

A condition involving damage to the optic nerve that results in partial or complete loss of vision. The optic nerve carries visual information from the eye to the brain, and when its fibers degenerate, visual acuity, color perception, and peripheral vision can all be affected.…

Proliferative Diabetic Retinopathy(also: PDR)

An advanced stage of diabetic retinopathy in which abnormal new blood vessels grow on the retina, causing bleeding, scarring, and progressive vision loss that can include blurred vision, floaters, dark spots, and partial or complete blindness. A major cause of acquired low…

Pupil Diameter(also: Pupil Size, Aperture Size)

The width of the opening in the iris through which light enters the eye, typically ranging from about 2mm in bright light to 8mm in darkness. Pupil diameter significantly affects visual quality because it determines how much of the eye's optical aberrations influence the image…

Retinitis Pigmentosa(also: RP, Retina Pigmentosa, Rod-Cone Dystrophy)

A group of inherited genetic disorders that cause progressive degeneration of the retina, leading to gradual vision loss. Initial symptoms typically include difficulty seeing in low light (night blindness) and loss of peripheral vision (tunnel vision). The condition often begins…

Retinopathy(also: Diabetic Retinopathy, Retinal Disease)

A group of eye conditions affecting the retina that can cause vision loss or blindness. Diabetic retinopathy, caused by damage to blood vessels in the retina due to diabetes, is one of the leading causes of blindness in working-age adults. Symptoms may include blurred vision,…

Visual Aberration(also: Optical Aberration, Refractive Error)

A deviation from ideal optical performance in the eye that causes images to appear blurred, distorted, or otherwise degraded on the retina. Visual aberrations include both lower-order aberrations (such as myopia, hyperopia, and astigmatism) and higher-order aberrations (such as…

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