A glossary of eye, optician and ophthalmologic eye terms

ACCOMMODATION: The ability to change focus.

ACUITY: Clarity of vision expressed as a fraction, such as 20/150. The smaller the denominator, the better the acuity. Far acuity is usually measured at 20 feet and near acuity at 14 inches. Normal vision without "corrective" lenses is defined as 20/20 at far and 14/14 at near.

AMBLYOPIA (LAZY EYE): A condition in which the brain suppresses the nerve impulses from one eye, giving it subnormal acuity. In most cases, there is nothing basically wrong with the suppressed eye, although it may turn inward or outward. A person with amblyopia is known as an amblyope.

ASTIGMATISM: A visual problem in which the eyeball and/or cornea is warped. The result is uneven focusing of light on the retina so that the image is blurred and distorted. Astigmatism usually diminishes at all distances.

CATARACT: A degenerative eye disease in which cells inside the eye's inner lens die and obstruct the passage of light. A cataract is not a tumour or growth but simply the accumulation of dead cells, which makes the inner lens cloudy. Cataracts can be removed surgically but complications from surgery sometimes cause blindness.

CILIARY MUSCLE: The circular muscle that surrounds the inner lens and makes it change shape.

CONVERGENCE: The ability to point the eyes at the same object at same time.

CORRECTIVE LENSES: Glasses or contact lenses that treat the symptoms of poor vision by compensating for the eye's optical defects.

DEVELOPMENTAL VISUAL PROBLEMS: Problems arising when a child's visual system fails to develop properly. Developmental visual problems can remain undetected throughout the person's entire lifetime.

DIOPTER: The unit of measurement of the refractive equal to the reciprocal of the focal length power of a lens, in metres.

DRY EYE SYNDROME: A condition in which the tear glands don't function properly, producing insufficient tear fluid or tear fluid with thewrong composition.

ENVIRONMENTAL THEORY: The theory that environmental factors such as stress, lighting, nutrition, posture, and excessive close work are the major causes of visual problems such as eyestrain, astigmatism, myopia, and cataract.

EXTRAOCULAR MUSCLES: A group of six muscles that surround the eyeball and move it in different directions.

GENETIC THEORY: The theory that visual problems are genetically determined.

GLAUCOMA: A degenerative eye disease usually caused by blockages in the eye's drainage system that increase the pressure inside the eyeball. Glaucoma often damages the optic nerve and is officially listed as a major cause of blindness.

HYPEROPIA (FARSIGHTEDNESS): visual problem in which the person sees far objects better than near objects. A person with hyperopia is called a hyperope. (PRONOUNCED HYPER-OH-PIA)

IATROGENIC PROBLEMS: Secondary problems caused by the treatment itself, such as side effects caused by drugs, complications caused by surgery, or loss of natural focusing power caused by "corrective" lenses. (PRONOUNCED YATRA-GENIC)

LASER SURGERY: The use of a laser to destroy cellular tissue, for example, treating glaucoma by drilling tiny drainage holes in the eye. Lasers are also used to treat myopia and astigmatism by vaporizing part of the cornea, thereby changing its curvature and refractive power.

MACULAR DEGENERATION: A degenerative eye disease in which cells die in the central part of the retina at the back of the eye, resulting in partial blindness.

MINUS LENS: A lens that makes objects appear smaller. Minus lenses have negative diopters of refractive power, for example, -5.00D, and are used to treat myopia. sees near objects better than far MYOPIA (NEARSIGHTEDNESS): A visual problem in which the person objects. A person with myopia is called a myope. (PRONOUNCED MY-OPIA)

MYOPIA MORBIDITY: Degenerative eye diseases caused by or associated with myopia, including cataract, glaucoma, macular degeneration, and retinal detachment. Myopia is officially listed as a major cause of blindness.

NEARPOINT STRESS: The major visual stress factor, caused by too much reading, computers, TV, or other close work.

OPHTHALMOLOGIST: A doctor who treats eye diseases by means of drugs and surgery. Many ophthalmologists also treat by means of "corrective" lenses or refractive surgery. visual problems

OPTICIAN: A technician who dispenses glasses and contact lenses.

OPTOMETRIST: A traditional optometrist is a doctor who treats visual problems by means of "corrective" lenses. A behavioral optometrist is a doctor who treats visual problems by means of vision therapy. Most optometrists are also licensed to prescribe various drugs and perform minor surgery.

ORTHOKERATOLOGY: A procedure that changes the curvature and refractive power of the cornea by means of special contact lenses. 

LENS: A lens that makes objects appear to be larger. Plus lenses have positive diopters of refractive power, for example, +5.00D, and are used to treat presbyopia and hyperopia.

PRESBYOPIA (AGING EYES): A visual problem in which the eye loses its focusing power due to the aging process, especially in people over forty. If the person previously had good vision, near objects may become blurred although distant objects can usually be seen clearly. If the person previously had myopia, astigmatism, or hyperopia, bifocals are usually prescribed. A person with presbyopia is called a presbyope. (PRONOUNCED PRESBEE-OPIA)

PROGRESSIVE UNDERCORRECTION: The use of a series of progressively weaker "corrective" lenses to improve vision and increase the eye's natural focusing power, usually in conjunction with vision therapy.

REFRACTIVE ERROR: A measurement of the eye's inability to focus light from a distant object onto the retina. Refractive errors are measured in terms of power of the "corrective" lens needed to compensate for them. For example, a -5.00D myope has 5 diopters of myopia, whereas a +3.00D hyperope has 3 diopters of hyperopia.

REFRACTIVE POWER: The ability of a lens to focus light. The lens can be an external lens or one of the eye's optical components such as the cornea.

RETINAL DETACHMENT: A leading cause of blindness in which the retina detaches from the supporting tissue at the back of the eyeball.

RK SURGERY: The use of a scalpel to make radial cuts in the cornea, thereby changing its curvature and refractive power.

STRABISMUS (CROSSED EYES): A condition in which the eyes point in different directions, causing double vision or suppressed vision in one eye.

STRESS-RELIEVING GLASSES: Special glasses that improve the performance of the visual system, usually in conjunction with vision therapy.

VISION: The total awareness resulting from information obtained by the eyes. Vision also depends on past experiences, current emotions, expectations, stress, nutrition, the general state of health, posture, bodily activities, and information received from the other senses.

VISION THERAPY: Commonly known as eye exercises, vision therapy consists of various techniques that improve the performance of the eyes and visual system, including acupressure, modification, biofeedback, hydrotherapy, stress reduction, behavior hypnosis, nutrition, ocular calisthenics, yoga, and syntonics. If lenses or prisms are used, vision therapy is referred to as optometric visual training.