Classic Optical Labs - Eyecare Terms and Definitions

Common Eye Disorders and Vision Terms

Accommodations
The ability of the eye to focus at varying distances without the help of an Ophthalmic Lens.

Amblyopia
A reduction or dimming of vision in an eye that appears to be normal. Also commonly known as lazy eye, amblyopia is an eye condition noted by reduced vision not correctable by glasses or contact lenses and is not due to any eye disease. The brain does not fully acknowledge the images received by the amblyopic eye. This almost always affects only one eye but may manifest with reduction of vision in both eyes.

Aphakia
Absence of the Crystalline Lens due to surgery or accident.

Aqueous Humor
A clear fluid between the Cornea and Crystalline lens. It is a refracting medium of the eye.

Astigmatism
Focusing error that tends to distort vision at all distances. In astigmatism, some directions in an image are more out of focus than others; as opposed to myopia where all directions are uniformly blurred. Even slight degrees of astigmatism may encourage headaches, fatigue and reduce concentration. Most astigmatism is caused by the shape of the front surface of the eye (the cornea) the cornea is flatter in one meridian than in another (a non-spherical cornea) or by slight tilting of the lens inside the eye. Most people have at least a very slight astigmatism.

Base Curve
The front surface curve of an Ophthalmic lens. This curve can be measured with a Lens Clock.

Bifocal
This is an Ophthalmic lens made of glass, plastic, or polycarbonate that contains one or more optical centers. Bifocals are prescribed when a patient needs a visual requirement for both distance and near.

Bridge
The distance between lenses when referring to a frame or mounting.

Cataract
A disease where the crystalline lens becomes dense, cloudy or opaque and does not properly transmit light. Most often related to aging.

Compound Lens
Contains a sphere power, a cylinder power, and an axis.

Conjunctivitis
Sometimes called pink eye, conjunctivitis is an inflammation of the blood vessels in the conjunctiva, the membrane that covers the sclera and inside of the eyelids. Conjunctivitis may be caused by bacteria or viruses, making it very contagious.

Cornea
The transparent anterior portion of the eye consisting of five layers of tissue and serves as the first refracting medium of the eye.

Crystalline Lens
Biconvex transparent lens located directly behind the pupil and serves as the second refractive medium of the eye.

Cylinder
A surface in a lens with two distinct meridians of unequal power. Used to correct astigmatism.

Decentration
A procedure used to line up the Optical Center of a lens with the patient's pupillary distance (P.D.) to avoid unwanted prism.

Diopter
A unit of measurement of lens power, usually expressed in quarters, such as 0.25, 0.50, 0.75, and 1.00.

Fovea
A small depression in the Retina of the eye near the Optic Nerve. It gives the sharpest vision.

Frame
Any shaped or styled appliance that holds an Ophthalmic Lens by complete encirclement of a rim.

Glaucoma
An eye disease where the inner pressure of the eye increases causing damage to the Optic Nerve. Can be controlled with drugs. If not treated, causes blindness.

Hyperopia
A refractive condition known as "Farsightedness."

Iris
Located in the eye behind the Cornea. It is a circular disk with a hole in the center. The Iris gives the eye its color.

Lens Measure
A sensitive Ophthalmic instrument used to measure the actual curvatures of an Ophthalmic lens. Also known as a "lens clock."

Lens Power
The actual strength of an Ophthalmic Lens. It is expressed as either a Plus or Minus or a combination of both.

Lens
A piece of Ophthalmic glass or plastic that has been shaped by grinding or bending. It is worn by a person to correct or to aid a visual defect.

Lensometer
An instrument used to measure the prescription of a lens, including the sphere power, cylinder power, axis, optical center, and prism power.

Millimeter Ruler
A small measuring device with markings located one millimeter apart from another.

Millimeter
A metric unit of measurement. Used to measure distance.

Mounting
An appliance that holds an Ophthalmic Lens on the appliance by screws, rivets, or clips.

Myopia
A refractive condition known as "Nearsightedness."

Oculus Dexter (O.D.)
Pertaining to the right eye.

Oculus Sinister (O.S.)
Pertaining to the left eye.

Oculus Uniter (O.U.)
Pertaining to both eyes.

Ophthalmic
Pertaining to the eye or to related functions, services, or materials for the eye.

Ophthalmologist
A Medical Practitioner who specializes in medical treatment, surgery, and vision care.

Optic Nerve
The part of the eye that carries all images to the brain for interpretation.

Optical Center
The point on a lens where a ray of light will enter without being bent, refracted, or disturbed.

Optical Dispenser
One who fills prescriptions written by Ophthalmologist and Optometrists.

Optometrist
One who practices Optometry. A vision specialist.

Pantoscopic Tilt
The bottom edge of the frame is closer to the face than the top edge.

Photochromic
A lens that has the ability to change color (commonly known as Photo-grey, Photo-brown, Photo-sun, or Transitions).

Plano (PL)
Refers to a flat lens surface or an area in a lens that has no refractive power.

Polairiscope
A device that uses two pieces of polaroid to determine stress or strain. Also used to determine if an Ophthalmic lens has been heat treated or chemically hardened.

Presbyopia
A refractive condition where a person can no longer see comfortably at his or her customary reading level.

Pupil
The hole in the Iris is called the pupil, and it controls the amount of light entering the eye.

Pupillary Distance
Also known as the P.D. This is a measurement of the actual distance between two pupils expressed in millimeters.

Refraction
The bending of light.

Retina
It is the light sensitive part of the eye. It is commonly referred to as the "Film" of the eye in the analogy of the eye and the camera.

Retroscopic Tilt
The top edge of the frame is closer to the face than the bottom edge.

Sclera
The white opaque covering of the eye, except for the Cornea. It helps to maintain the shape of the eye.

Segment Height
The measurement taken for a multi-focal lens. This measurement is taken from the patient's lower eyelid to the bottom eyewire of the frame

Segment
The portion of a bifocal or trifocal that is used for near vision.

Single Vision Lens
This is an Ophthalmic lens made of glass, plastic, or polycarbonate that contains only one Optical Center.

Sphere
A lens in which its power is equal in all meridians.

Temple
The part on a frame to be worn over the ear.

Trifocal
This is an Ophthalmic lens made glass, plastic, or polycarbonate that contains two or more optical centers so the wearer is given continuous vision from near to infinity.

Vitreous Humor
A jelly- like substance filling most of the inner eye. Refracts light and maintains eyeball shape.