Glossary
A description of the various medical/ophthalmic terms used throughout this guide.
A
Acanthamoeba keratitis A serious form of inflammation of the cornea which can result in blindness if left untreated. It is caused by a parasite which is found in contaminated lakes, pools and tap water.
Astigmatism A form of refractive error in which the cornea is oval shaped rather than round: this causes light to focus on two points at the back of the eye rather than the one. The result is blurred vision.
Axis A measurement used by the optician to determine the exact angle of the lens in order to correct a visual problem such as myopia. This is noted down on an eye prescription.
B
Bifocal lens
A type of contact lens which consists of two focal areas: one area controls distance vision and the other area controls near to vision.
C
Computer vision syndrome
This is where the eyes become dry and sore as a consequence of staring at a computer screen for a long period of time. This reduces the blink rate which means that the eyes become tired and strained and vision is blurred.
Contact lens
The small, plastic disc which is placed over the cornea of the eye to correct defective vision, e.g. long sightedness. Commonly worn as a corrective device but is also worn for cosmetic and therapeutic reasons also.
Cornea
The transparent tissue at the front of the eye which covers the pupil and iris. This allows light to pass through to the back of the eye which enables us to see. This is the part of the eye which is covered by a contact lens.
D
Daily disposable lenses
A popular type of contact lens: this lens is designed to be worn once before being thrown away. This removes the need for lens aftercare.
Disinfectant solution
The solution used to clean and soak contact lenses overnight. The lenses are placed in a storage case with this solution which removes protein deposits and other substances from the lenses.
Dry eyes
This occurs when the eyes fail to produce enough tears, usually from staring for long periods of time without blinking. This causes a burning sensation in the eyes which also feel itchy and sore. Blurred vision is another symptom.
E
Extended wear lenses
A type of contact lens which is worn from a week up to a maximum of 30 days, and without the need to be removed during that time.
F
Farsightedness This is where the eye has a short, flat shape which affects the ability to focus clearly on objects near to. The medical term for this is hypermetropia or hyperopia. It is more commonly known as long sightedness.
G
Gas permeable lenses
These lenses are produced from a more rigid material compared to soft lenses but allow a greater proportion of oxygen to reach the eye. They were the preferred lens before the advent of soft lenses.
These lenses are stronger and longer lasting than soft lenses.
They are often prescribed for conditions such as astigmatism and presbyopia.
H
Hypermetropia
The medical name for farsightedness: also known as long sightedness.
Hyperopia
See above.
I
Implantable lens
This usually refers to an intraocular lens: a type of contact lens which is inserted behind the cornea or iris to correct a refractive error. This is a permanent type of lens.
Iris
The coloured circle at the front of the eye. The iris controls the dilation and contraction of the pupil.
J
None at present.
K
Keratitis The medical name for inflammation of the cornea: there are several different types of keratitis which include acanthamoeba keratitis, ulcerative keratitis and microbial keratitis.
The cornea becomes sore, red and inflamed and cannot tolerate bright light. Eyesight is hazy and blurred.
Keratoconus A progressive condition in which the cornea gradually changes to a cone shape which causes it to bulge at an angle. This affects the ability to focus clearly and requires correction with contact lenses or glasses.
L
Laser eye surgery
A procedure in which a laser is used to reshape the cornea to correct refractive errors such as short sightedness and long sightedness.
Long sightedness
See hypermetropia: this is where objects which are near to appear blurred and out of focus.
M
Multifocal lenses
A type of lens which contains different focal areas (known as corrective powers) which enables the wearer to view objects close to and at a distance.
Myopia
The medical name for short sightedness: sometimes known as near sightedness. This is where the eye is too long and steep in shape which affects its ability to see objects clearly at a distance. This is the most common form of refractive error.
N
Nearsightedness
See myopia: an inability to see objects clearly at a distance. It is also known as far sightedness.
O
Optician
A specialist trained in many aspects of eye care which includes contact lens fitting.
Orthokeratology
The name of a type of contact lens which is designed to be worn at night time only. This allows it time to reshape the cornea and improve faulty vision.
P
Presbyopia
An age related condition in which the lens of the eye becomes stiffer and less able to focus on objects which are close to. This occurs around the age of 40 or so and requires the use of reading glasses to view small print.
Pupil
The round black spot in the centre of the eye which opens and closes in response to the amount of light it perceives. This is regulated by the iris.
Q
None at present.
R
Refractive error
A medical term used to describe a condition whereby light is not properly focussed onto the retina. This affects the ability of the natural lens of the eye to focus on an image – whether that is close to or at a distance. This results in conditions such as myopia and hypermetropia.
Retina
The area at the back of the eye which receives an image via the lens of the eye: it converts this into a series of signals which are then transmitted to the brain. This is known as eyesight.
S
Soft lenses
A type of lens which is made from a soft, water based plastic or more frequently, silicone hydrogel which makes them easy to wear and comfortable. But they are less durable and more prone to tearing than gas permeable lenses and need to be replaced more often.
Toric lenses
A type of contact lens often worn to correct astigmatism.
U
None at present.
V
None at present.
W
Wetting solution The name of the cleaning solution used to lubricate a gas permeable lens before insertion. This often makes it easier to place the lens onto the eye. It can also be applied to ease any dryness in the lens caused by wearing if for several hours at a time.
X
None at present.
Y
None at present.
Z
None at present.