Eye Care Glossary: Common Vision & Eye Terms Explained

A quick reference for common eye-care terms you may see in your prescription or hear during an eye examination at Vision Concern.

Astigmatism

An irregular curvature of the cornea or lens that causes blurred or distorted vision at any distance. Corrected with glasses, contact lenses (often toric lenses) or, in some cases, refractive surgery.

Myopia (Nearsightedness)

A condition where distant objects appear blurry while close objects are clear, caused by the eye focusing light in front of the retina rather than on it. Corrected with concave (minus-powered) lenses.

Hyperopia (Farsightedness)

A condition where close objects appear blurry while distant objects may be clearer, caused by the eye focusing light behind the retina. Corrected with convex (plus-powered) lenses.

Presbyopia

An age-related reduction in the eye's ability to focus on close objects, typically becoming noticeable in the early-to-mid 40s. Often corrected with reading glasses, progressive lenses or multifocal contact lenses.

Progressive Lenses

Lenses that correct near, intermediate and far vision within a single lens, without a visible line dividing the zones, unlike traditional bifocals.

High-Index Lenses

Lens materials with a higher refractive index than standard plastic, allowing a thinner and lighter lens for the same prescription strength — useful for stronger prescriptions.

Keratoconus

A progressive condition where the cornea thins and bulges into a cone-like shape, causing irregular astigmatism that often cannot be fully corrected with standard glasses or soft contact lenses. Specialty lenses such as scleral lenses, or treatments like corneal cross-linking, may be considered by a specialist.

Glaucoma

A group of eye diseases that damage the optic nerve, often associated with elevated eye pressure, that can cause irreversible vision loss if untreated. Usually develops without early symptoms, making regular eye examinations important for early detection.

Dry Eye

A condition where the eyes do not produce enough quality tears to stay lubricated, causing irritation, a gritty feeling, or sometimes watery eyes as a reflex response.

PD (Pupillary Distance)

The distance between the centers of your pupils, measured to ensure your lenses are positioned correctly in your frame.

Frequently Asked Questions

What is the difference between myopia and hyperopia?

Myopia (nearsightedness) makes distant objects blurry, while hyperopia (farsightedness) can make close objects blurry. They are corrected with opposite lens powers.

At what age does presbyopia usually start?

Presbyopia typically becomes noticeable in the early-to-mid 40s, though this varies by individual.

Can keratoconus be corrected with regular glasses?

In milder cases, glasses may help, but as keratoconus progresses, specialty options such as scleral lenses are often needed, and a specialist should assess corneal progression.

Why does my prescription mention high-index lenses?

High-index lenses are usually recommended for stronger prescriptions, since they are thinner and lighter than standard lens materials for the same correction.