Glossary for Patients

• Aberration
  A distortion seen through a lens. Non-convergence of rays of light
• Accommodation
  Ability of eye to automatically change focus - see at one distance and then at another.
• Aftercare
  A never-ending period of time needed to check eyes and lenses after they are fitted.
• Allergy
  Abnormal sensitivity reaction of the body to substances that are usually harmless.
• Amblyopia
  Also called lazy eye; diminished sight in one eye.
• Anterior chamber
  Area behind the cornea and in front the iris and lens filled with fluid called aqueous humour. Usually about 3mm deep.
• Antioxidant
  Substance: inhibits oxidation and can guard the body from the damaging effects of free radicals. Molecules with one or more unpaired electrons, free radicals can destroy cells and play a role in many diseases. Antioxidants may help prevent macular degeneration and other serious eye diseases.
• Aphakia
  Condition of eye where crystalline lens has been removed.
• Aqueous humour
  Clear fluid in the eye - provides nutrients and determines intraocular pressure.
• Astigmatism
  Normal condition where the eyeball is not spherical.
• Bifocal
  A lens that focuses for distance and reading.
• Bifocal
  A lens that focuses for distance and reading.
• Blank
  A singular piece of lens material that is yet to be trimmed to specification- a raw cast button.
• Calcium
  A constituent of tears that is readily deposited on areas of a lens that has lipid contamination. It becomes crusty and irritating often attracting more proteins as a result of foreign body sensation.
• Capsular bag
  Sack positioned behind the iris that contains the crystalline lens.
• Cataract
  Name given to crystalline lens when it becomes opaque, resulting in impaired vision.
• Choroid
  Layer of blood vessels and pigments (usually brown or blue) - lies beneath the sclera (the white of the eye). Often mistakenly called the iris.
• Cones
  Colour-sensitive nerve endings in retina.
• Conjunctiva
  Transparent skin on the front of eye covering the white visible part of the eye and underside of eyelids.
• Conjunctivitis
  Inflammation of conjunctiva.
• Convergence
  Ability of eye to turn inward - causes eyestrain, blurred vision, with near tasks such as reading.
• Cornea
  Clear part of the eye covering the iris and pupil - lets light into the eye, permitting sight.
• Corneal implants
  Devices (such as rings or strips) placed in the eye, usually to correct vision.
• Corneal lens
  Contact lens that sits within the boundaries of the cornea -usually a rigid lens.
• Corneal topography
  Process of using a camera/computer system to map the cornea for refractive surgery, contact lens fitting and corneal disease management.
• Corneal ulcer
  Wound in the surface of the eye caused by injury, dryness due to lack of tear production, or infection.
• Cosmetic lens
  A lens used to cover an unsightly eye or to change the appearance of the eye.
• Crystalline lens
  Variable lens inside the eye behind the iris responsible for one third of the focusing of the eye and changing the focus from distance to reading.
• Daily wear
  Soft contact lenses worn every day for six months up to a couple of years. They require daily cleaning and disinfecting, as well as a periodic enzymatic soak (usually once a week).
• Diabetic retinopathy
  Leaking of retinal blood vessels in advanced or long-term diabetes, affecting the macula or retina. Vision can be seriously distorted or blurred.
• Diameter
  Overall diameter of a lens. Although it may refer to one of the zones or optic sizes.
• Dioptre
  Unit that measures the refractive (light-bending) power of a lens; eyecare practitioners use it in eyeglass and contact lens prescriptions. A negative number refers to nearsightedness, while a positive number refers to farsightedness. For example, someone with -8.00 dioptre lenses is very nearsighted, while someone with +0.75 dioptre lenses is only slightly farsighted.
• Dispensing Optician
  An optician who makes up spectacles or fits contact lenses to a written prescription.
• Disposable lenses
  Contact lenses with a limited life span (daily, one week, two weeks).
• Dk
  Permeability value of a given contact lens material - low Dk is around the 2- 30 mark, Mid Dk is between the 30- 50 mark & High Dk is above these.
• Dry eye
  Lack of sufficient lubrication and moisture in the eye. Most dry eye complaints are temporary and easily relieved; dry eye syndrome, also called keratoconjunctivitis sicca, is chronic and needs more advanced treatment by an eyecare practitioner.
• Enzymatic cleaner
  A cleaner that removes protein deposits and other debris from contact lenses. It's recommended for use either daily, weekly, or monthly.
• Extended wear lenses
  Lenses designed to be kept in for longer periods.
• FDA
  Food & Drug Administration - A United States government body - oversees medical devices, including contact and Intraocular lenses. The FDA must review these products before they can be marketed in the US.
• Fenestration
  Hole drilled through contact lens to increase tear flow.
• Fovea
  A depression in the retina that contains only cones (not rods), and that provides acute eyesight.
• Gas Permeability
  Amount of air that can go through a lens.
• Glaucoma
  Condition where internal pressure of the eye increases causing damage to the retina and possibly blindness.
• H.E.M.A
  Hydroxy ethyl methacrylate - The backbone of many hydrophilic contact lenses. HEMA has a nominal water uptake of 38% giving an expansion factor of approx 1.20. This material was one of the first to be used in hydrophilic contact lenses and by adding other monomers, such as VynilPyrrolidone(VP) ,by cross linking , the water content can be raised . For example, CF42 = Hema / VP. Hema is a very stable & safe material once polymerised.
• HAPTIC
  Means by which the optic portion of a lens is held in position - generally used in scleral lenses.
• Hybrid
  Hybrid of materials - a mixture of RGP & Hydrophilic monomers.
• Hydrophilic
  Have an affinity for water. Soft contact lenses are hydrophilic.
• Hypermetropia
  Long sight normal eye condition where the eye is too small and eyes have to over focus to see clearly.
• Hyperopia
  Long or farsightedness - near objects are blurry, but far objects are in focus.
• Implant
  Plastic lens inserted into the eye during surgery to replace crystalline lens that has been removed.
• Intraocular lens (IOL)
  Artificial lens that an opthalmic surgeon places in a patient's eye after removing the eye's natural lens. Like a contact lens, it has a built-in refractive power tailored specifically to the patient's visual condition.
• Iris
  Coloured part of the eye that is in fact a diaphragm opening and shutting to let in more or less light into the eye. Also opens under other influences (eg. Fear).
• Keratitis
  Inflammation of the cornea.
• Keratoconic
  A design of contact lens that tends to have a very steep/small back optic radius that is used in the fitting of keratoconic corneas. A keratoconic cornea is usually as a result of the thinning of the cornea and the resultant intraocular pressure distends the corneal tissue. In severe cases the cornea can rupture.
• Keratoconjunctivitis
  Inflammation of the cornea and conjunctiva.
• Keratoconus
  Condition in which the cornea develops a cone-shaped bulge that can result in major blurring and distortion.
• Keratometer
  Instrument used to measure the curves on the cornea. (Ophthalmometer)
• Lens
  Nearly spherical body in eye - focuses light rays onto retina.
• Lipid
  Lipids are fatty acids present in tears. They are very attracted to areas of the surface of contact lenses that are dry or hydrophobic. In hydrophilic lenses they penetrate the matrix and become sites for deposition of calcium and phosphates.
• Liquid lens
  Lens made of tears trapped between the contact lens and the cornea.
• Macula
  Curved spot at the centre of the retina where 'cones' are concentrated to give very accurate sight and colour vision.
• Monovision
  Vision correction method for those with presbyopia in which one eye is corrected for near vision and the other for far, either through contact lenses or refractive surgery. Eliminates the need for reading glasses, but decreases depth perception.
• Moulded lens
  Lens that is made by casting between two pre-made moulds. A very efficient way of making lenses but initial setup cost is high and not easily variable on parameters.
• Multifocal
  Type of spectacle or contact lens design - includes more than one focal area, such as bifocals or trifocals.
• Myopia
  Nearsightedness - visual images come to a focus in front of the retina, resulting in defective vision of distant objects.
• Myopic creep
  Increase in myopia induced by contact lenses
• Non ionic
  Refers to the surface charge of a material. A material is classed as non ionic if it contains less than 0.2% ionisable material. All of the Contamac hydrophilic materials are classed as non ionic and they repel a larger proportion of deposits.
• Ophthalmic Medical Practitioner
  Doctor who examines eyes.
• Ophthalmic Optician
  Name given to opticians who examine eyes. Now almost obsolete as the name optometrist is used.
• Ophthalmic Surgeon
  An ophthalmologist who also carries out eye surgery.
• Ophthalmologist
  Doctor who specialises in treating eye disease.
• Ophthalmoscope
  An instrument used to examine the inside of the eye through the pupil.
• Optic Nerve
  Second cranial nerve that carries information from the retina to the brain
• Optometrist
  An optician who specialises in examining eyes and prescribing optical appliances such as spectacles and contact lenses.
• Orthokeratology
  Procedure where doctor fits special gas permeable contact lenses to reshape cornea and correct errors like nearsightedness. Often, patients wear the lenses just at night. (ortho-k).
• PEG
  Poly Ethylene Glycol is a soap like substance used in the polishing mix when tumble polishing PMMA IOLs. It acts as a cleaner and lubricant.
• Perspex
  Trade name (ICI) for acrylic resin.
• Phakic IOLs
  High plus power Intraocular lenses to correct aphakia (Severe long sight as a result of no natural or artificial intraocular lens present in the eye).
• Phosphate
  Phosphates are present in tears and combine with fatty acids and calcium to make hard, rounded deposits on the surface of hydrophilc lenses. These are commonly known as "calculii".
• PMMA
  Old-fashioned hard contact lenses were made of PMMA, (polymethyl methacrylate) and non-oxygen permeable. Now rigid (Rigid Gas Permeable) lenses contain other polymers that allow oxygen to reach the eye.
• Posterior chamber
  Part of the eye behind the iris and in front of the lens.
• Presbyopia
  Inability of the eye lens to focus incoming light because of age-related stiffening of the lens tissue - result is blurred vision at reading distance and eyestrain.
• Prism
  Wedge shape to a lens that has the optical effect of displacing the image by a given amount in dioptres. Prism is used in special lenses such as a toric to provide a ballast effect to prevent the lens from rotating.
• Prism ballast
  Specifically making a lens with a thin top and a thick bottom so that it is heavier at the bottom.
• Protein
  Proteins are naturally present in animal tears and become deposited on contact lens surfaces during wear (and storage if not removed by cleaning). Initially they make the lens surface wettable and "comfortable" but soon become mineral in character - causing discomfort and cloudy vision. The eye deposits more protein to counter this and a cycle of deposition is started. Enzyme tablets are used to remove the deposits.
• Pupil
  Round, dark centre of the eye - opens and closes to regulate the amount of light the retina receives.
• Reduced optic
  Process by which a lens is made thinner by making the centre smaller.
• Registered Optician
  Term used in the UK to describe a practise where both optometrists and dispensing opticians work together.
• Retina
  Layer at the back of the eye that has millions of light-sensitive nerve cells connecting to the brain via the optic nerve.
• Retinal blood
  vessels Transparent blood vessels that supply the retina that are seen with the ophthalmoscope during an eye examination.
• Retinoscope
  Instrument used to reflect light off the retina so that the prescription can be gauged objectively.
• Rigid lens
  A hard (rigid gas permeable) lens rather than a soft lens.
• Rods Light
  sensitive nerve cells in the retina that tell light from dark and are responsible for night vision.
• Sclera
  White outer coat of the eye that surrounds the optic nerve.
• Soft contact lenses
  Hydrated hydrophilic contacts made of gel-like plastic/ polymers containing varying amounts of water.
• Spectacle blur
  Reduced vision noticed particularly with spectacles when contact lenses are removed.
• Stress
  Uneven tension across a mass of material - usually due to poor polymerisation and annealing or can be induced by machining or heat. Instability and warpage can be detected using polarised light
• Suction holder
  A rubber sucker used to remove contact lenses.
• Surfactant
  Cleaner used to clean the surface of the contact lens.
• Swell factor
  Value that represents the amount a hydrophilic material expands by when immersed in saline or water. Linear swell describes the increase in diameter and radial swell describes the amount a base curve changes. For example, CF38 tends to have a linear sell of around 1.20.A lens made with a dry diameter of 11.80mm will expand to 14.16 mm when fully hydrated in saline.
• Tensile strength
  Measurement of how strong a material is. Tested by stretching so see the force needed to stretch a material. Elongation to break value expressed as a percentage and the modulus of elasticity.
• Tint
  Generally refers to handling tint in contact lenses. Usually it is a pale blue overall colour to assist in lens manipulation. Normally it is a chemical dye but can be a pigment.
• Tonometer
  Instrument used to measure internal eye pressure.
• Toric lens
  Contact lens specially designed with two different optical powers at right angles to each other to correct astigmatism.
• Truncation
  Special edge shaping to stop lens rotating on the eye.
• Ultra-Violet
  Harmful end of spectrum light, which causes ageing of the eye.
• Vitreous humour
  Transparent jelly filling globe between crystalline lens and retina.
• Water content
  Amount of water in a soft lens (hydrated hydrophilic) material presented as a percentage. Generally the higher the value the softer and less strong the material will be but will have a higher Dk value.
• Wettability
  The surface wetting of a lens material is normally expressed as an angle ie 240 - poor wettability is indicated by a high value > 40.