Astgmatism
Anterior Chamber
Aqueous
Bifocal
Cataracts
Colour Blindness
Conjunctivitis
Cornea
Crystalline Lens
Diabetes / Diabetic Retinopathy
Dispensing Optician
Dry Eyes
Emmetropia
Field of view
Glaucoma
Hypermetropia
Iris
Lens
Long Sightedness
Macular Degeneration
Mono Vision
Myopia
Ophthalmologist
Optic Nerve
Optician
Optometrist
Plano
Presbyopia
Pupil
Refraction
Retina
Sclera
Short Sightedness
Vitreous Cavity
Astigmatism occurs when your cornea is shaped like a rugby ball with two different curvatures. Images appear blurred or ghost-like because light rays are refracted unequally. In extreme cases, images both near and far, appear blurred. Many people who have myopia also have astigmatism.
Positioning a cylindrical lens in front of an astigmatic eye will refract the light in one direction more than in the other. Basically the light passes through the cylindrical lens in two different directions. The power of the lens is not the same all over. It is stronger in certain areas to compensate for the irregular curves on the astigmatic eye. When corrected, an astigmatic person will than see distance and close objects clearly.
The portion of the eye behind the cornea and in front of the iris which contains the aqueous fluid.
The liquid contained in the anterior chamber of the eye; it is produced by the ciliary body behind the iris, and flows through the pupil into the anterior chamber before draining away at the anterior chamber angle, around the periphery of the iris at its junction with the cornea.
A type of spectacle or contact lens design that includes two focal areas: one for near, one for distance.
A cataract is a cloudiness of the eye's lens, which lies between the front and back areas of the eye. Cataracts blur and scatter light entering the eye, thereby reducing vision. Cataracts are part of the natural ageing process with about half of the population having a cataract by the age of 65 and nearly everyone over 75 having at least one.
A non-specific term for congenital or acquired impairment of colour discrimination. Technically it is an incorrect term, as most individuals who are colour “blind” see colours; they just have difficulty distinguishing certain colours from others. A more precise term is “colour vision deficiency.” It seems that more males are affected, with 7% of males showing this deficiency, and only about 0.5% of females. Colour vision deficiency is not a disease or degenerative condition, though occasionally an acquired colour vision deficiency may be a symptom of other health problems.
Conjunctivitis is an inflammation of the conjunctiva, the thin, transparent layer that lines the inner eyelid and covers the white part of the eye. Common symptoms of conjunctivitis are red watery eyes, inflamed inner eyelids, blurred vision, an itchy feeling in the eyes and, sometimes, a watery discharge.
The three main types of conjunctivitis are infectious, allergic and chemical. The infectious type, commonly called "pink eye" is caused by a contagious virus or bacteria. Your body's allergies to pollen, cosmetics, animals or fabrics often bring on allergic conjunctivitis. And, irritants like air pollution, noxious fumes and chlorine in swimming pools may produce the chemical form.
The cornea is the transparent, outer "window" of the eye and is the main focusing element of light entering the eye. The cornea is made up of 5 layers of tissue with the outer layer’s (the epithelium) main job being to protect the eye. The epithelium is made up of transparent cells that have the ability to regenerate quickly, usually within 3 days to provide rapid healing to minor injuries. The inner layers of the cornea are also made up of transparent tissue, which allows light to pass and predominantly provide strength to the eye.
The natural lens of the eye, a transparent structure suspended behind the iris. The lens focuses light rays on the retina and changes shape to allow the eye to focus for different distances. (See Lens)
Diabetes is a disease that occurs when the pancreas does not secrete enough insulin or the body is unable to process it properly. Patients with diabetes are more likely to develop eye problems such as cataracts and glaucoma, but the disease’s affect on the retina is the main threat to vision. Most diabetic patients develop changes in the retina after approximately 20 years with the effect of diabetes on the eye being called diabetic retinopathy.
Over time, diabetes affects the circulatory system of the retina. In the early stages of the disease, known as background diabetic retinopathy, the arteries in the retina become weakened and leak, forming small, dot-like haemorrhages. These leaking vessels often lead to swelling in the retina and decreased vision. Diabetics are entitled to free annual Eye Examinations from the NHS.
A person who is qualified in the dispensing of spectacles and specialises in the fitting of frames and all areas of lens work. This person may also be additionally qualified to fit contact lenses using a valid prescription from an optometrist.
Dry eye syndrome is a lack of lubrication and moisture in the eye. Its consequences range from constant irritation to inflammation of the front tissues of the eye. Persistent dryness, scratching and burning in your eyes are signs of dry eye syndrome. Some people also experience a "foreign body sensation," the feeling like there's something in the eye. Sometimes watery eyes can result from dry eye syndrome, because the excessive dryness works to over stimulate the watery component of your eye's tears.
The image of a distant object is focused correctly on the retina and therefore the eye does not require any correction. Emmetropia is the ideal state of the eye. The focus of the eye is set for distance vision without the need for glasses or contact lenses. Emmetropia occurs when the curvature of the cornea, the shape of the lens and their distances from each other and the retina are in harmony. The cornea and lens focus the rays of light from an object perfectly on the retina, creating a sharp image.
The area that is visible through the lens of an optical system, i.e. your eyes.
Glaucoma is a condition in which the pressure of the fluid (aqeous humor) inside the eye is too high, either because too much fluid has been produced, or because it's not draining properly. Left untreated symptoms include optic nerve damage and vision loss. Glaucoma patients are entitled to free annual Eye Examinations from the NHS.
Hypermetropia means long sight and is where the image is formed behind the retina. This could be because the eye is too short, or the cornea or the lens does not refract the light enough. A hypermetropic person has blurred vision when looking at objects close to them, and clearer vision when looking at objects in the distance. By placing a convex lens in front of a hypermetropic eye, the image is moved forward and focuses correctly on the retina. A hypermetropic person will then see distance and close objects clearly.
This is the part of the eye which is responsible for one's eye colour. The main function of the iris is to control the size of the pupil by dilating or constricting its muscles, thereby allowing more or less light into the eye.
The lens is the part of the eye immediately behind the iris that performs fine tuning of light rays upon the retina for focusing. The lens performs this function by altering its shape to become thinner or thicker as necessary. In general with persons under 40, the lens is soft and pliable, allowing for fine focusing from a wide variety of distances. For individuals over 40, the lens begins to become less pliable, making focusing upon objects near to the eye more difficult. This is known as presbyopia. As people reach their 60’s or 70’s, the lens sometimes becomes cloudy and hard (cataract), preventing light from entering the eye.
The macula is found at the centre of the retina where the incoming rays of light are focused and is responsible for what we see straight in front of us. This vision is needed for detailed activities such as reading and writing and our ability to appreciate colour.
Because macular degeneration is an age-related process it usually involves both eyes, where the delicate cells of the macula become damaged and stop working. However both eyes are not necessarily affected at the same time. With many people the visual cells simply cease to function, like the colours fading in an old photograph - this is known as 'dry' degeneration.
This is a contact lens fitting technique that is an alternative to bifocal glasses, bifocal contacts or reading glasses. It may be used with either soft or oxygen permeable contacts. One eye is fitted with a contact lens for distance vision, and the other eye is fitted for near vision. Although it is an effective technique, it does have disadvantages. For example, many people who use monovision report compromised depth perception.
Myopia means short sight and is where light from an object forms an image before it reaches the retina. This could be because the eye is too long, or the cornea or crystalline lens refracts (bends) the light too steeply. A myopic person has clear vision when looking at objects close to them, and blurred vision when looking at objects in the distance. By placing a concave lens in front of a myopic eye, the image moves back to the retina so it will be clear. A myopic person can then see distance and close objects clearly.
Ophthalmologists are medical doctors who are eye specialists generally based in hospitals. They perform eye examinations, treat disease, and perform surgery; some also specialize in contact lenses. Some ophthalmologists may have opticians and contact lens technicians working with them, who are specially trained to fit contact lenses.
The optic nerve takes information from the retina as electrical signals and delivers it to the brain where this information is interpreted as a visual image. The optic nerve consists of a bundle of about one million nerve fibres.
A place where eye tests are carried out by an Optometrist. A person can be the proprietor of a practice and as such be called an optician, however they could have no professional qualifications for testing eyes.
Optometrists examine eyes for both vision and health problems, prescribe glasses, and fit contact lenses. They can also prescribe many eye related medications and participate in pre and post-operative care.
Optometrists in the UK have generally completed a 3 year degree and then undertaken a further year in a supervised clinical practice with a qualified optometrist.
A technical term meaning having no optical power; light passes through without being deviated from its original path or focused.
During middle age, usually beginning in the 40s, people experience blurred vision at near points, such as when reading or working at the computer. This happens to everyone at some point in life, even those who have never had a vision problem before.
When people develop presbyopia, they find they need to hold books, magazines, newspapers, menus and other reading materials at arm's length in order to focus properly. When they perform near work, such as writing, they may have headaches or eyestrain, or feel fatigued.
The black circle in the centre of the eye, surrounded by the coloured iris. The pupil controls how much light enters the eye. When you are in a bright environment, the pupil becomes smaller to allow less light through. When it is dark, the pupil expands to allow more light to reach the back of the eye.
A measurement of the eyes to determine the level of visual acuity (sharpness). Most refractions are performed by optometrists, though many ophthalmologists do them as well.
The retina consists of fine nerve tissues which line the inside wall of the eyes and acts like the film in a camera. Its primary function is to transmit images to the brain via the optic nerve. When your vision is perfect, the light rays coming into your eye focus precisely on this part of the eye.
The white part of your eye that you see when you look at yourself in the mirror is the front part of the sclera. However, just like an eggshell surrounds an egg and gives an egg its shape, the sclera, a tough, leather-like tissue, surrounds the eye and gives the eye its shape.
see Myopia
The vitreous cavity is located behind the lens and in front of the retina and is filled with a clear gel-like fluid called the vitreous humour. The gel’s purpose is to provide a spherical shape to the eye. The vitreous may develop small clumps known as “floaters,” which are more common in nearsighted people.
