Back To Basics Glossary
For Eyewear Professionals and Consumers


AMBLYOPIA, LAZY EYE: A condition that affects just two to three percent of the population. But, if left uncorrected, this vision problem can have a very big impact on those affected. Central vision fails to develop properly, usually in one eye, which is called amblyopic. A related condition, strabismus, sometimes causes amblyopia.

Untreated amblyopia may lead to functional blindness in the affected eye. Although the amblyopic eye has the capability to see, the brain "turns off" this eye because vision is very blurred, and the brain elects to see only with the stronger eye.

Amblyopic or 'Lazy' Eye

Clearer vision occurs in the eye with normal sight
Blurry vision occurs in the lazy eye, even with glasses

Signs and Symptoms

Amblyopia generally develops in young children, before age six, and symptoms often are noted by parents, caregivers or health-care professionals. These symptoms include:

Overall poor visual acuity
Squinting or completely closing one eye to see


Trauma to the eye at any age can cause amblyopia, as well as a strong uncorrected refractive error (nearsightedness or farsightedness) or strabismus. It's important to correct amblyopia as early as possible, before the brain learns to entirely ignore vision in the affected eye.


Amblyopic children can be treated with vision therapy (which often includes patching one eye), atropine eye drops, the correct prescription for Nearsightedness or Farsightedness, or surgery.

Vision therapy exercises the eyes and helps both eyes work as a team. Vision therapy for someone with amblyopia forces the brain to see through the amblyopic eye, thus restoring vision.

Sometimes the eye doctor or vision therapist will place a patch over the stronger eye to force the weaker eye to learn to see. Patching may be required for several hours each day or even all day long and may continue for weeks or months. If you have a lot of trouble with your child taking the patch off, you might consider a prosthetic contact lens that is specially designed to block vision in one eye but is colored to closely match the other eye.

In some children, atropine eye drops have been used to treat amblyopia instead of an eye patch. One drop is placed in your child's good eye each day (your eye doctor will instruct you). Atropine blurs vision in the good eye, which forces your child to use the eye with amblyopia more, to strengthen it. One advantage is that it doesn't require your constant vigilance to make sure your child wears the patch.

Recently a study compared atropine therapy with patching in 419 children age 3 to almost 7 and found it an effective alternative. As a result, some previously skeptical Eye Care Professionals are using atropine as their first choice over patching.

Patched Eye

Anissa's Fun Patches

Innovative amblyopia patches help children comply with their amblyopia treatment.
You can help your child accept patching more readily. Anissa's Fun Patches, for instance, require no adhesive because they slide onto the temple of an eyeglass frame.

However, atropine does have side effects that should be considered: light sensitivity (because the eye is constantly dilated), flushing and possible paralysis of the ciliary muscle after long-term atropine use, which could affect the eye's accommodation, or ability to change focus.

If your child has become amblyopic due to a strong uncorrected refractive error or a large difference between the refractive errors of both eyes, amblyopia can be treated with eyeglasses or contact lenses in the correct prescription. Your ECP, Eye Care Professional, may prescribe an eye patch along with the new glasses or contact lenses.

Surgery is best for amblyopic children with an underlying physical problem, such as strabismus. The surgery corrects the muscle problem that causes strabismus so the eyes can focus together and see properly.

ASTIGMATISM: A blurred vision condition produced by a football-shaped cornea, which is too steep in one meridian and too flat in another. An astigmatic cornea focuses light in two different places in the eye, adversely affecting both near and distance vision. See CYLINDER below.

Objects appear blurry at all distances

BEFORE Corrected Vision                     AFTER Corrected Vision          

AXIS: An expression in the form of numbers that corresponds to the orientation of the cylinder power of an ophthalmic lens in terms of degrees from 0 to180.

BRIDGE: That part of the frame front that connects the eyewires and holds the frame in place at the nose.

BRIDGE TYPES: KEYHOLE BRIDGE: A type of bridge that fits only on the sides, and does not touch the top. Resembles a keyhole. SADDLE BRIDGE is a type of bridge that sits uniformly over the nasal crest.

CATARACT: A clouding of the lens of the eye. More in depth cataract data, here.

Experience simulated eye diseases here. Cataract simulator. Detached retina simulator. Diabetic retinopathy simulator. Glaucoma simulator. Macular degeneration simulator.

CYLINDER: An expression in the form of numbers indicating the amount of astigmatism correction in an ophthalmic lens. See ASTIGMATISM above.


Left image, spherical lens with no cylinder.
Vertical and horizontal meridians are equal.
Right, lens with cylinder to correct astigmatism.
Vertical and horizontal meridians are unequal.

DBL: The Distance Between Lenses, i.e., the least distance between the two mounted lenses, or the frame's bridge size.

DIOPTER: A measurement of an ophthalmic lens refractive power equal to the reciprocal of the focal length of a lens in terms of meters, e.g., a 2.00 Diopter lens will bring parallel rays of light to a focus at a half meter, i.e., .50 meters. Also, the measurement of the degree to which light converges (a plus Diopter, +2.00D, lens will correct farsighted vision), or the degree to which light diverges (a minus Diopter, -2.00D, lens will correct nearsighted vision).

"It is how well the eyewear makes contact with the
Patient that ultimately defines Ophthalmic Dispensing."

DISPENSING OPTICIAN, LICENSED DISPENSING OPTICIAN or REGISTERED DISPENSING OPTICIAN, LDO or RDO (depending on the State's designation): EYE CARE PROFESSIONAL, ECP, herein defined as a Board Certified and-or State Licensed Eye Care Practitioner who specializes in the design of prescription eyewear, i.e., lenses, frames and contact lenses, which includes the duplicating, measuring, inspecting, and verifying of prescription lenses, and any subsequent frame Alignment and other Adjustments, which includes the Final Fitting, whereby the Patient's visual comfort, the long term comfort and wearability of their eyewear is the primary objective. Watch 'What Is An Optician'.

NOTE: An expanded definition as defined by the U.S. Dept. of Labor, Bureau of Labor Statistics: "Designs, measures, fits, and adapts lenses and frames according to a written optical prescription or specifications; assists with selecting frames; measures for size of eyeglasses and coordinates frames with facial and eye measurements and optical prescriptions; prepares a work order for an optical laboratory containing instructions for grinding and mounting lenses in an ophthalmic frame; verifies exactness of finished lenses; adjusts frame and lens positions to fit the wearer; shapes or reshapes frames. Includes contact lens Opticians." See also OpticiansForChange.com.

"When's the last time you saw or heard a retail optical
ad that promoted the custom fitting of eyewear?"

Opticians are Eyewear Professionals. Opticianry
is ultimately defined by how well the eyewear makes
contact with the Patient, not by the number of Customers served.
For the truly skilled Optician, the standard of care must include a
customized design and handcrafted fitting of eyewear on each Patient.

DISTOMETER: A device used for measuring Vertex Distance. When an eyeglass prescription reaches a certain strength, the vertex distance between the eyes and the Patient's eyeglasses must match the vertex distance between the Patient's eyes and the Phoropter, i.e., the instrument used during the comprehensive eye examination to determine refractive error, at the time of the Doctor's refraction. Patients can experience problems with an Rx of about 6 Diopters of power, give or take. A 1mm difference between the working distance of the Phoropter at the time of their exam and the fitting distance of their corrective lenses can cause significant refractive error relative to the Patient. Therefore it is important to match the vertex distance between that of the Phoropter and their glasses, or modify the optics in order to accommodate the actual fitting distance of the eyeglasses. The Distometer is an instrument used for measuring and calculating this compensation.

Conversion Scale and Distometer

The Distometer measures the vertex distance and compensates for the average eyelid thickness. The Patient closes their eyes in a relaxed fashion with the eyeglasses in position while the Optician places the flat end on the Patient’s eyelid directly behind the lens. As the elongated button at bottom of photo above is pushed the Distometer arm moves from its resting position. As it lightly touches the back of the lens, the Optician observes the reading. The rotating chart above is designed to calculate the correct Rx compensation. From here, the Optician can adjust the frame and fit the glasses at that same distance or determine the necessary changes to be made in the Rx. Note: The further away the lenses are positioned from the cornea, the smaller the field of view.

ECP or EYE CARE PROFESSIONAL: Any Health Care Professional who specializes in a) the medical examination or treatment of eye disease or injury; b) refracts the eye for the purpose of correcting vision error; c) designs prescription eyewear, i.e., lenses, frames and contact lenses, which includes the duplicating, measuring, inspecting, and verifying of lenses, and any subsequent dispensing or delivery, including Alignment and other Adjustments, which includes the Final Fitting of prescription and safety eyewear, and contact lenses. NOTE: The Florida Board of Opticianry is an entity within the Florida Department of Health, which has jurisdiction over Florida Eye Care Professionals. Also see DISPENSING OPTICIAN, LDO and see Letter to Eye Care Professionals.

EYEWEAR: A medical prosthesis, i.e., an ophthalmic device which acts as a vision aid and-or eye protection for a dysfunctional or otherwise at-risk system of sight, inclusive of both eyeglasses and contact lenses. For the purposes of the Hands-on Frame Fitting Course, the word EYEWEAR refers to any streetwear, sunwear, safety, athletic, or other occupational or avocational prosthesis, utilizing corrective or plano lenses, which are worn in combination with an ophthalmic frame.

EYEWIRE: That portion of the eyeglass frame front into which the lenses are inserted or mounted and which is connected to its opposite by the bridge.


CATARACTS: The natural lens in the eye gradually becomes less clear as we get older. When opacities develop in the lens and the lens gets too hazy, vision will be impaired. When the cataract affects the vision to the extent that one cannot read or see distant objects comfortably, cataract surgery may be required.

DIABETES: Diabetic Patients should have a dilated retinal examination each year. Laser treatments have proven to slow the progression of retinal eye disease for many Patients. Diabetes often stimulates the growth of new blood vessels in the back of the eye, which ultimately leak and damage the retina. If this condition is discovered early, laser treatment can destroy these vessels.

GLAUCOMA: Glaucoma gradually destroys the optic nerve tissue in the back of the eye. The greatest danger of glaucoma stems from the fact that the disease is painless and without obvious symptoms until significant damage has occurred. The most common cause is from pressure being too high inside the eye, but vascular disease and other diseases can also cause glaucoma. A full eye exam includes checking the pressure of the eye, screening for peripheral vision defects and analyzing the appearance of the optic nerve. If you are diagnosed with glaucoma, your eye care professional may prescribe medications that lower the eye pressure. Most forms of glaucoma are successfully treated with eye drops. Laser treatments and eye surgery are secondary treatments that offer alternative ways to treat more advanced glaucoma.

FRAME: That portion of a pair of eyeglasses that is designed to hold the lenses in the proper position before the eyes.

Hands on the Patient Frame Fitting is an
artful handcraft, which is fast disappearing.

HANDS-ON DISPENSING AND DELIVERY: Herein defined as those procedures, which involve eyewear adjustments performed by a skilled Dispensing Optician, which specifically include, a) the visual and 'touch and feel,' hands on the Patient, tactile assessment of the frame, while it is in-place, on the face of the Patient, in order to determine any misalignment, and b) any subsequent multi-dimensional hands on the Patient, tactile, artful 'touch and feel' handcrafting that is required to refit, align, adjust, reshape, bend, stretch, twist and sculpt the components of the frame in order to personalize the eyewear for maximum visual comfort and wearability. See example.

SPECIAL NOTE: This level of craftsmanship can be accomplished only after a visual as well as a tactile, i.e., touch and feel, assessment of the frame, in-place, on the Patient, and requires the removal and re-placement of the eyewear directly on the Patient, BY THE OPTICIAN, as many times as necessary to complete the procedure. (Unfortunately, many of today's Dispensers make no contact with either the Patient or their eyewear while in place, on-the-face, whereby it is impossible to make a significant assessment or subsequent multi-dimensional adjustments to the frame. This practice is akin to a Dentist making no direct contact with a Patient while attempting fit dentures. Sadly, latter generation Dispensers give little or no attention to fitting a new frame after it arrives from the lab, presumably four-point inspected on a flat surface by the lab technicians. Just as in the case of fitting a set of dentures, a frame must ultimately be custom fitted to the variable dimensions of the Patient, not the one-dimensional surface of a flat table. The lab only zeroes-out any frame misalignment in lieu of anticipated adjustments by the Optician.)

Hands-on frame fitting requires direct contact
between the Optician and the Patient.

Furthermore, a properly executed hands-on, in-place, on-the-face assessment, and frame fitting procedure requires not only appropriate communications between the Dispenser and the Patient, but some direct physical contact must occur as well. A proper hands-on fitting involves the repeated removal and re-placement of the frame on and off the Patient by the Dispenser until such time as the fitting is completed, which depends of course on the experience of the Dispenser, any asymmetric features of the Patient, and the type and design of the eyewear. See example. The Dispenser cannot rush the procedure. Much time is actually saved in the long run when the fitting is done with sensitivity and patience whereby Patient return visits are minimized.

HEALER: One who contributes to making a person whole.

HEALING ARTS: Those skillful practices, which contribute to the health and wellness of those to whom they are applied. See also Ophthalmic Health and Wellness.

HEALTH CARE PRACTITIONER: Any professional individual or organization, which provides health and wellness products and services to the public. NOTE: The Florida Board of Opticianry is an entity within the Florida Department of Health, which has jurisdiction over Florida Health Care Practitioners.

HYPEROPIA: Another word for FARSIGHTEDNESS, which is a common vision problem, affecting about a fourth of the population. People with hyperopia can see distant objects very well, but have difficulty focusing on objects that are up close. Farsightedness can be corrected with glasses or contact lenses to change the way light rays bend into the eyes. If your glasses or contact lens prescription begins with plus numbers, like +2.50, you are farsighted. You may need to wear your glasses or contacts all the time or only when reading, working on a computer or doing other close-up work.

Hyperopia or Farsightedness
Near objects appear blurry, far objects appear clear

 BEFORE Corrected Vision                     AFTER Corrected Vision 

IN-DEPTH LIFESTYLE INTERVIEW: Each Patient needs to undergo an adequate lifestyle interview in order to establish their primary and secondary needs whether they be for work or play. Many times their vision needs require multiple pairs of eyewear. Therefore the interview must include the appropriate amount of time and dialogue for the Optician to discover the true needs of the Patient. (Note: This interview must take place absent bias on the part of the interviewer with regard to profit incentives in order to be successful.) The absence of this interview is a primary reason for unhappy Patients to return for remakes or to request refunds. Here's an example. Many times Refractionists, Many times Refractionists, i.e., Optometrists and Ophthalmologists, will make an entry on their prescriptions such as "No-line Bifocals" or "Progressive Lenses," both of which refer to a Progressive Addition Lens or PAL. Too many times this is a subjective entry on their part, which is made in the absence of any discussion with the Patient, and minus any explanation to the Patient as to why a Progressive Lens is better, or how the lens works, or what other options are available. Of course, these points are better left to the Optician to give more complete coverage during an in-depth lifestyle interview, but which too often never occurs. See video.

LASIK SURGERY or LASER VISION CORRECTION: A medical procedure in which a flap is surgically cut in the cornea and gently folded back. An Excimer Laser is used to reshape the cornea into a flatter shape (this is reminiscent of a contact lens that corrects vision by forming a new shape on the cornea). The flap is then put back in place, acting like a natural bandage. The healing process is quick and the discomfort level is quite low.

Following the procedure Patients will often say that they did not feel anything, and could see well the very first day. Most people have improved vision in 24-48 hours but it must be noted that each person will heal at a different rate. Vision, although greatly improved immediately after surgery, often continues to improve for some weeks, even months.

LASIK is not for everyone. People's eyes are different and it may not be the best course of treatment for you. Consult your eye care professional.

LENSMETER, Lensometer or Vertometer, is the instrument used to read the dioptric power of an ophthalmic lens and to locate the optical center of the lens. See also Using a Lensmeter. 

Optician using a Lensmeter

Estelle Glancy, inventor of first Lensometer

MASTOID: A protruding bony area in the lower part of the skull that is located behind the ear in humans and many other vertebrates and serves as a site of muscle attachment. The mastoid process contains small air-filled cavities called mastoid cells that communicate with the middle ear. This area is not uniformly flat on the majority of human skulls. On the contrary, the mastoid has a somewhat wave-like topographical variance that can range from subtle to severe, which requires that handcrafted form-fitting procedures be applied to the temple-ends in order to hold the eyewear in place and thereby afford long-term wearability. The mastoid area is not so sensitive to touch but is sensitive to pressure for most patients.

NOTE: Contrary to popular opinion and practice, full contact with a LIGHT TOUCH OF THE SKULL, NOT THE EARS, is the primary means by which the frame should be held in place for long-term comfort and wearability. The ears should NOT be used as the main reference in order to stabilize or hold the eyewear in place. Ears act only as a 'stop'. It is the uniform contact of the frame temples with the mastoid area, with no pressure, that provides the greatest degree of stability and comfort.

The mastoid process

MYOPIA: Another word for NEARSIGHTEDNESS, which is a vision problem experienced by up to about one-third of the population. Nearsighted people have difficulty reading highway signs and seeing other objects at a distance, but can see for up-close tasks such as reading or sewing. Nearsighted people often have headaches or eye strain and might squint or feel fatigued when driving or playing sports. If you experience these symptoms while wearing your glasses or contact lenses, a comprehensive eye exam as well as a new prescription may be needed. Myopia occurs when the eyeball is slightly longer than usual from front to back. This causes light rays to focus at a point in front of the retina, rather than directly on its surface. Nearsightedness runs in families and usually appears in childhood. This vision problem may stabilize at a certain point, although sometimes it worsens with age. This is known as myopic creep. Nearsightedness may be corrected with glasses, contact lenses or eye surgery.

Myopia or Nearsightedness
Distant objects appear blurry, near objects appear clear

BEFORE Corrected Vision                     AFTER Corrected Vision          

OPHTHALMIC: An expression which means anything that pertains to the eye or is situated near the eye.

OPHTHALMIC DISPENSER: Any Eye Care Professional, ECP, who specializes in the design of prescription eyewear, i.e., lenses, frames and contact lenses, which includes the duplicating, measuring, inspecting, and verifying of lenses, and any subsequent delivery, Alignment and other Adjustments, including the Final Fitting of the eyewear. See also DISPENSING OPTICIAN, LDO.

"It is how well the eyewear makes contact with the
Patient that ultimately defines Ophthalmic Dispensing."

OPHTHALMIC DISPENSING: As herein defined is those frame adjustments performed by a qualified ECP, Eye Care Professional, usually an Optician, which includes, a) the fullest discovery and maximum consideration of the Patient's visual needs, b) the assistance and advice to the Patient regarding the appropriate choice of lens design and frame selection, c) the duplicating, measuring, inspecting, and verifying of lenses, and d) any subsequent Gross Frame Alignment and Subtle Frame Adjustments, including the Final Fitting.

OPHTHALMIC HEALTH AND WELLNESS: As herein defined is that state of well-being wherein a Patient's visual health and comfort is supported, and the long term wearability of their eyewear is provided and maintained.

OPHTHALMIC PATIENT: As herein defined is one who needs or receives health related services having to do with their vision and-or eyewear.

ECPs, Eye Care Professionals

Ophthalmologist, Optician, and Optometrist


.) OPHTHALMOLOGIST, MD or DO: EYE CARE PROFESSIONAL, ECP, who is a State Licensed-Board Certified Health Care Practitioner who specializes in the diagnostic, surgical, and other medical treatments as well as the refraction of the eye in order to determine any refractive visual error and the means by which the error can be corrected. An Ophthalmologist is a Physician, i.e., a Doctor of Medicine or Doctor of Osteopathy, who specializes in the comprehensive care of the eyes and visual system in the prevention of eye disease and injury. An Ophthalmologist must complete four or more years of college level premedical education, four or more years of medical school, one year of internship, and three or more years of specialized medical and surgical training and experience in eye care. An Ophthalmologists is a Physician who is qualified by lengthy medical education, training and experience to diagnose, treat and manage all eye and visual system problems, and is licensed by a state regulatory board to practice medicine and surgery. The Ophthalmologist is a medically trained specialist who can deliver total eye care: primary, secondary and tertiary care services, i.e., vision services, contact lenses, eye examinations, medical eye care and surgical eye care, and diagnose general diseases of the body. The steps taken by Ophthalmologists to treat a patient`s eye are the following:

1) Take a good history and listen to the patient and don`t miss or dismiss any complaint.
2) Ask about systemic diseases that may affect the eye as diabetes and hypertension and about drugs the patient regularly takes.
3) Ask if the condition is recurrent or this was the first time and if recurrent, what previous medications were taken.
4) After a good history you are supposed to have reached the diagnosis or a differential diagnosis that is to be confirmed with examination.
5) Do full ophthalmological examination including fundus and IOP (Intra Ocular Pressure) measurement.
6) If needed supplement the examination with one or two investigations specific to confirm the diagnosis or give clues for treatment or prognosis.
7) Explain for the patient his or her case fully including prognosis.
8) Explain the treatment given and how to apply it and its importance and the consequences of discontinuing the treatment without doctor`s order.
9) Give the patient dates for follow up and explain the danger of not coming in for the specified appointment times.
10) Let there be a way for the him or her to communicate with you if any problems or complaints occurred before the next follow up visit.
11) Finally and most important be kind to the patient and give him or her adequate time during the examination and if their case is out of your capabilities to treat or of another subspecialty, refer them to whomever can give them better service.



.) OPTICIAN, i.e., LICENSED DISPENSING OPTICIAN, LDO, or REGISTERED DISPENSING OPTICIAN, RDO, depending on the State's designation, EYE CARE PROFESSIONAL, ECP, who is a State Licensed-Board Certified Health Care Practitioner who is qualified to fit, adapt, and dispense eyewear, i.e., eyeglasses and contact lenses or other optical devices, based on the written prescription of a licensed Physician or Optometrist, or to duplicate same. Depending on the State, an Optician's education may consist of at least (2) two years of study in Opticianry science at an accredited college of ophthalmic dispensing or a state approved apprenticeship program. Florida and Arizona require American Board of Opticianry and National Contact Lens Examiners certification, in addition. (Some states require only national certification.) In addition, an Optician must pass a State Board examination. In order to maintain licensure, an Optician must fulfill approved Continuing Education requirements. (NOTE: A Dispensing Optician is related to the health care industry just as a Registered Pharmacist is related to the health care industry. Both fulfill the prescription needs of their respective Patients.) See also DISPENSING OPTICIAN.



.) OPTOMETRIST, OD: EYE CARE PROFESSIONAL, ECP, who is a State Licensed-Board Certified Health Care Practitioner who specializes in the refraction of the eye in order to determine any refractive visual error and the means by which the error can be corrected. Optometrists are primary Eye Care Professionals for the eye who are trained and state licensed to provide primary eye care services. These services include comprehensive eye health and vision examinations; diagnosis and treatment of eye diseases and vision disorders; the detection of general health problems; the prescribing of glasses, contact lenses, low vision rehabilitation, vision therapy and medications; the performing of certain surgical procedures; and the counseling of Patients regarding their surgical alternatives and vision needs as related to their occupations, avocations and lifestyle. The Optometrist will have completed pre-professional undergraduate education in a college or university, and four years of professional education at a College of Optometry, leading to a Doctor of Optometry, OD, degree. Optometrists must complete a residency under the laws of some states.


Most Refractionists use a Phoropter to
determine corrective lenses for the Patient.

PHOROPTER: The instrument that contains multiple lenses for use by a Refractionist, i.e., Optometrist, OD, Ophthalmologist, MD, or Osteopathic Physician, DO, during a comprehensive eye examination to determine any refractive error. Any prescription for eyeglasses or contact lenses is determined mostly with this instrument. In some cases a digital Auto-Refractor is used, but it is not nearly as accurate as the manually operated Phoropter.

PRESBYOPIA: A term used to describe a condition whereby a person needs vision assistance by way of READING GLASSES and-or BIFOCALS or TRIFOCALS. During middle age, usually beginning in the 40s, people experience blurred vision at near points, such as when reading, sewing or working at the computer. There's no getting around it -- this happens to everyone at some point in life, even those who have never had a vision problem before. Currently an estimated 90 million people in the United States either have presbyopia or will develop it by 2014. This is generating a huge demand for eyewear, contact lenses, and surgery that can help presbyopes deal with their failing near vision.

Objects appear blurry at near and intermediate distances

BEFORE Corrected Vision                     AFTER Corrected Vision

BEFORE Corrected Vision                                    AFTER Corrected Vision          

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 embroidery or handwriting, they may have headaches or eyestrain or feel fatigued. Presbyopia is caused by an age-related process. This is different from astigmatism, nearsightedness and farsightedness, which are related to the shape of the eyeball and caused by genetic factors, disease or trauma. Presbyopia is generally believed to stem from a gradual loss of flexibility in the natural lens inside your eye.

These age-related changes occur within the proteins in the lens, making the lens harder and less elastic with the years. Age-related changes also take place in the muscle fibers surrounding the lens. With less elasticity, the eye has a harder time focusing up close. Other, less popular theories exist as well.

PRESCRIPTION: The document, which expresses the lens powers and other pertinent details, and is signed by the attending Refractionist, i.e., Optometrist, OD, Ophthalmologist, MD, or Osteopathic Physician, DO.

PRISM: An element added to the prescription if the Patient's eyes need help working more effectively together, and-or to remain in proper alignment.

Eyeglass Rx

Eye Care Professional using a Pupillometer*


The Pupillometer measures the distance between
pupils via the light reflected from the corneal surfaces.

PROGRESSIVE ADDITION LENS (PAL): A multifocal lens whose corrective powers change progressively throughout the lens. Each area of correction is blended invisibly to the next, so these lenses do not have the lines typically associated with bifocals or trifocals and afford the most “natural” vision at all distances: near, far, and intermediate.

Left: Typical Progressive Lens Design
Right: Computer Progressive Lens Design

PUPILLARY DISTANCE or PD: The measurement in millimeters of the distance between the eyes for distance vision, far PD, and for reading, near PD. This measurement is used to determine placement of the optical centers of the lenses in the Patient's eyewear. For more accuracy, this measurement is taken using a specialized instrument called a *Pupillometer (see photo above), which measures the distance between the light reflected from the surface of the cornea. Using a pupillometer produces a much more precise measurement, which is particularly important in designing progressive addition lenses, PALs and for lenses of significant spherical and-or cylindrical power ranges. NOTE: There can be a significant variable in the distance between one corneal apex reflection to the center of the nose and the other, which means that the optical centers of the lenses will be placed asymmetrically in the final design of the lenses in order to accommodate this disparity. See Facial Asymmetry.

Refractionist: Optometrist, OD, or Ophthalmologist, MD, or Osteopathic Physician, DO.

RX: This is an abbreviation of the word, PRESCRIPTION, that refers to the document, which expresses the lens powers and other pertinent details, and is signed by the attending Refractionist, i.e., Optometrist, OD, or Ophthalmologist, MD, or Osteopathic Physician, DO.

SLAB OFF: Also known as bicentric grinding. Bicentric grinding is a type of lens fabrication process in which base-up prism is ground on the lower portion of the lens to redirect light as a patient gazes downward. This technique allows the patient to fuse the images and prevent prism as the eye travels down the vertical meridian of the lens. The term slab-off came about because the technique makes the finished lens look as if someone removed a small section of the bottom portion. Of all the ways to correct vertical imbalance, slab-off is by far the most common technique used. BTW: There are six methods of correcting this imbalance: Two pairs of glasses, i.e., one for reading and another for distance; dis-similar segments; r-compensated segments; Fresnel press-on prisms; prism segments; and of course, slab-off. See How To Calculate Slab Off Prism. See Slab Off Calculator.

SPRING HINGE: A type of hinge on eyeglass frames that flexes, making the frames more durable. Spring hinges also help keep the eyewear in proper alignment and help reduce the need for some adjustments.

TEMPLES: Generally defined as the hinged extensions on each side of the frame front, which when the frame is worn, extend along each side of the head, and in most styles, bend down behind the ears. Temples are made to be reshaped to follow the contours of the skull (see example) and avoid direct contact with ears, while resting evenly against the skull with minimum pressure, whereby they act to hold the eyewear comfortably in place. See also Variations on Styles of Temples.

TEMPLE-END: That part of the temple that extends down behind the ear and makes direct contact with the mastoid portion of the skull. The temple-end is designed to be reshaped to follow the contours of the skull whereby it acts to stabilize and hold the eyewear in place for long term comfort and wearability. The temple-ends, with all gaps and space removed, and making full contact with the skull, NOT THE EARS, are the primary means of holding the eyewear in place.

Form-fitting the Mastoid Complex
With a Handcrafted Mastoid Dip and Wrap

Every Patient deserves a sufficiently handcrafted,
multi-dimensional, form-fitting frame adjustment, e.g.,
gaps and spaces are removed from between the frame's
temples and the skull behind the ears, in order to enhance
comfort, stability, and long term wearability. Full contact with
a light touch of the skull, NOT THE EARS, is the primary means
by which the frame should be held in place for long-term comfort.


BEFORE temple-end is in out-of-the-box condition,
i.e., it doesn't make contact with the Patient's skull,
whereas the AFTER temple has been form-fitted with
an added handcrafted mastoid dip and mastoid wrap.
It now fits the mastoid bone like a glove since it has been
shaped to make full, direct contact with this Patient's skull.
The customized temple-ends become invisible when worn
and the resultant fit avoids pressure and is extremely comfortable.
Note: This skill cannot be learned virtually, i.e., via lecture or online.
This skill is acquired only by handcrafting the eyewear using direct, face
to face, on the Patient, tactile, touch and feel contact with the Patient. The
availability, knowledge and skilled use of related handcrafting tools is essential.
Also, keep in mind that online merchants are incapable of providing this service.

TRIAL FRAME AND LENSES: The Trial Frame and Lens Set is an important aid to the Optician. A Trial Frame and Lenses can be used to determine the Patient's visual acuity before a new Rx is ordered, give the Patient a preliminary real-world experience of their new prescription, and assist the Patient in determining lens design, i.e., bifocal, trifocal or PAL.

Trial Frame and Lenses
"A picture is worth a thousand words."
Trial Frame and Lenses can be used to demonstrate a new Rx.
This gives the Patient the visual experience of various lens designs.

VERTEX DISTANCE: The distance between the back surface of a corrective lens, i.e. glasses (spectacles) or contact lenses, and the front of the cornea. Increasing or decreasing the vertex distance changes the optical properties of the system, by moving the focal point forward or backward, effectively changing the power of the lens relative to the eye. Since most refractions are performed at a vertex distance of 14mm, the power of a corrective device fitted at a different vertex distance may need to be compensated to effect the same correction of the Doctor's initial refraction. Usually, when the lens power exceeds ±6.00 or ±7.00 diopters, depending on the Patient, vertex distance must be considered as an important factor. See also Distometer. NOTE: A Refraction is that portion of a comprehensive eye exam that is performed using a Phoropter.

WRAP-AROUND EYEWEAR (WRAP): Type of eyeglass lens-frame that curves around the head, from the front to the side. Wrap-around sunglasses tend to offer extra sun protection because the lenses usually hug close to the face and protect the delicate tissue around the eye as well. Get the rap on wrap-arounds here. See Advisory on Frame Selection here.



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