Glossary of eyesight terms
the eye's process of adjusting its focus from far to near.
Acuity: the fineness of detail the
eye can distinguish, see resolution
AMD: Age related Macular Degeneration:
see macular degeneration
Astigmatism: a focusing distortion
which is present at all distances, it can be cancelled out by a
cylindrical component in an ophthalmic prescription (marked CYL
on prescriptions). The angle of slant of the distortion is called
Autorefractor: an instrument used
by opticians to give a rough estimate of the eyes' focusing errors
Axis: see Astigmatism
Bates Method: a system of eye exercises
which aims to reduce myopia by altering the tone of muscles associated
with focusing the eye.
Bi-Focal: a spectacle lens which
has one section for distance and one for near work.
Blur, Blur circle: when an object
is out of focus each point of the object is spread out in a circle.
The image is blurred.
Cataract: a clouding of the lens
or cornea of the eye which obscures vision.
Ciliary Muscle: a ring of muscle
inside the eye which adjusts the shape of a flexible lens to focus
the eye at different distances.
Contact Lens: a dished transparent
disc that rests against the cornea to alter its focusing power
Convergence: the amount the eyes
rotate towards each other to point at a near object.
Cornea: the transparent domed window
at the front of the eye.
Corneal Transplant: an operation
to replace a cornea that isdamaged or diseased
CYL,Cylinder: see astigmatism
Diopter: the measure of lens strength.
=1/(focal length in metres)
Emmetropia: the state of normal vision
Emmetropisation: the process of an
eye changing shape towards normal vision
Eye Chart: a chart displaying letters
or symbols in a range of sizes used to determine focusing ability.
(See Snellen) Eye Exercise: various
exercise systems for improving focusing or convergence
Eye Strain: aching muscles around
the eyes usually resulting from the brain struggling to interpret
blurred or dissimilar images from the eyes.
Focus: to bring light rays from an
object together to form an image
Glaucoma: increased pressure of the
fluid inside the eye.
Hypermetropia: see hyperopia
Hyperopia: the eyes cannot focus
on near objects but see better in the distance
Iris: surrounds the pupil of the
eye. It expands and contracts to change the size of the pupil and
control the amount of light entering the eye.
Keratoconus: a mis-shaped cornea
which cannot focus clearly. Sometimes a contact lens will sometimes
help. Keratometry: measuring the
curvature of the cornea
Lazy Eye: when the brain favours
one eye the other may become weaker - a lazy eye
Lens: a transparent disk with curved
surfaces used focus light
Lens Implant: an artificial lens
used to surgically replace a diseased lens in the eye
Long Sight: see hyperopia
Macular: the central part of the
retina where detailed focusing takes place
Macular degeneration: a condition
which destroys the macular causing the loss of central, and detailed
vision Multifocal: a spectacle lens
which has several sections for focusing at different distances.
Myopia: the eyes can focus very near
but cannot focus in the distance.
Myopic: decribes an eye or person
Pinhole: a small hole which can be
looked through giving the eye an artificially small pupil.
Pinhole Glasses: spectacle frames
containing opaque screens containing several pinholes. Used to relax
or exercise the eyes.
Pinhole Test: a visual test using
a pinhole to establish whether poor vision is due to poor focussing
or fue to physiological or neurological factors.
Presbyopia: the loss of focusing
flexibility of the eye with age making it more difficult to focus
Pupil: the variable hole in the middle
of the iris which admist light into the eye.
Resolution: a measure of the ability
of the eye to distinguish fine detail.
Retina: the light sensitive lining
of the rear part of the eye. it coverts the light image falling
on it into nerv signals to the brain.
Retinoscopy: the technique of looking
into the eye with an optical instrument to observe the retina.
Short Sight: see myopia
Snellen: a system for measuring the
accuity of focusing using eye charts. The result is expressed as
a fraction eg 20/20
Varifocal: a spectacle lens which
has graduated focusing strength from top to bottom