Eye terminology explained
Words your optometrist might use…
The terms here are the most commonly used by your optician, most will only be of use in special cases or with people with ‘complex’ prescriptions.
However, if you would like to know a little more about your eyes and the words used to describe their health please read on!
Any defect or a distortion in any optical system.
The process by which the eye increases its power to focus on a near object, by effectively changing the shape of the crystalline lens.
ACUITY, VISUAL (Often abbreviated to V.A.)
The capacity of the eye to clearly see the detail of an object at a specific distance.
A lens, or an optical system, of zero power.
A condition characterised by low V.A. that is not correctable by optical means.
A defect in the refractive state of the eye, e.g. myopia, astigmatism, etc.
This when there is a difference in the prescription of each eye, typically greater than 1.00D
A condition in which one eye is myopic and the other is hypermetropic.
The ocular condition in which the crystalline lens of the eye is absent, or has been
Any curved surface that is not spherical, e.g. elliptical
A condition of the eye where the principal meridians have different refractive errors, requiring a toric lens to fully correct the vision. (Often caused when the corneal surface is not spherical, being more like the surface of a barrel or a rugby ball).
For more information on astigmatism please click here.
Relating to both eyes.
An instrument designed for detailed examination of the eye, used particularly in contact lens practice. (Often referred to as a slit-lamp)
A chronic inflammation of the eyelid margins.
For more information on blepharitis please click here.
The angle formed by the upper and lower lids at the nasal and temporal ends.
Partial or complete loss of transparency of the crystalline lens substance or its
For more information on cataracts please click here.
A surface shaped like the inside of a sphere.
Movement of the eyes turning inwards, i.e. towards each other.
A surface shaped like the outside of a sphere.
The transparent anterior portion of the eye.
The displacement horizontally and/or vertically of the optical centre of a spectacle lens – away from the boxed centre – to coincide with the centre of the patient’s pupil.
The unit of measurement of refractive power of a lens.
(Double vision) A condition where objects are seen ‘double’.
The region of the retina, where the optic nerve joins the eyeball.
Defect of an optical system resulting in an image that does not correspond to the
shape of the object.
Movement of the eyes, turning away from each other.
Perfect sight, when light from an object at infinity is sharply focused on the retina.
The muscles attached to the outside of the eyeball that control the movement of the eyes. (There are six extrinsic muscles)
The act of directing the eyes to an object so that its image is formed on the most sensitive part of the retina.
An instrument that measures the power of a spectacle lens, or contact lens.