Eye Glasses FAQ

Frames are identified by manufacturer/designer, model number or name, size, and color information. Size information contains the horizontal measurement of each lens in millimeters (i.e. 47) and bridge size (the distance between the lenses) i.e. 18. This information can help you in sizing a frame for your face. To better understand the frame size, double the first number and add the second. This will give you the distance across the full front of the frame. For example, a frame size of 47/18 means that the frame measures 112 mm across (47 x 2 + 18 = 112).

Frame size may also contain the temple length (including the portion going behind the ear) in millimeters such as 145. Therefore a frame size would be written 47/18 or 47-18 or 47/18-145. Color may be noted as a description such as gunmetal, other manufacturers use a color number. NeoVision’s opticians will help you in choosing the right size frame for the best possible fit.

Your eyeglass prescription contains information regarding the lens power required to correct your vision problems. It consists of spherical power, cylindrical power, cylinder axis, bifocal addition, and prism power. Your prescription will contain only those numbers that are pertinent for your vision correction, for example, if you do not have astigmatism, you would not have a cylindrical power and axis information in your prescription. Most prescriptions do not contain prism power.

This is the main part of your prescription. This number denotes the strength of the lens as measured in diopters.

A diopter is a unit of measurement that is simply the inverse of the focal distance of the lens as measured in meters. For example, if a lens has a strength of 2 diopters, then parallel light rays that pass through this lens will focus together at a distance of 1/2 meter (50 cm) away from the lens.

If there is no value under the cylinder heading, then you have a simple prescription. If there is a value under this heading, then you have astigmatism. Like sphere power, the cylinder power is also measured in diopters.

Yes, there are two ways of writing a prescription for astigmatism. Some prescriptions are written in (-) cylinder and some are written in (+) cylinder. These prescriptions are equal even though they may not appear so.

Inter-pupillary distance (PD) is the distance from the center of the pupil in one eye to the center of the pupil in the other eye. A PD measurement ensures that the center of the lenses line up with the center of your pupil. Before your prescription lenses are cut into the shape of your frame, the pupillary distance needs to be measured. This measurement is then used so that the optical center of each lens can be lined up with your pupils in order to give optimal visual clarity.

PD measurements for distance and near vision are different, like 62/59, the first number is your distance PD and the second is for your near PD (for reading-only glasses). For people with asymmetric eyes, PD measurement for each eye is done separately (called “monocular PD”), like 30.5/31.5. The first number is for the right eye (O.D.) and the second number is for the left eye (O.S.).

Anisometropia is a condition where there is a significant difference in the refractive errors of the two eyes. If this condition is present in infancy and is undetected or untreated, it often results in the development of lazy eye or amblyopia in the weaker eye. The greater the amount of the difference, the more likely the development of lazy eye will be. A problem can occur when glasses are made for an anisometropic individual. The difference in the powers of the lenses induces a prismatic difference that can cause double vision in off-center areas of the lens, which can be compensated for by the use of slab-off prism.

Bifocal segment height is measured from the bottom of the lens to the margin of the lower eyelid.

Progressive segment height is measured from the bottom of the lens to the center of the pupil.

No, there is none. A tall person may need shorter seg height and a shorter person may need a higher seg height.

Yes, the seg height can be raised either by bringing the nose pads together or by adding a pantoscopic tilt.

Light rays are diverged by minus (concave) lenses and converged by plus (convex) lenses.

Light rays passing through the optical center (OC) of a lens are not refracted. With proper PD measurements, your eyes are centered at the optical center of the lens.

For taking your unique fitting measurements, your physical presence is absolutely necessary. We will need to pre-adjust the frame on your face before ordering your glasses.

Plus (convex) lenses are used for correcting hyperopia (far-sightedness) and presbyopia (aging eye vision).

Center is the thickest part of a plus (convex) lens.

Center is the thinnest part of a minus (concave) lens.

An aspheric lens is flatter than a spherical lens.

Cornea has 70-80% of eye’s focusing power.

A lens with no corrective power is called plano.

The procedure is called surfacing which involves grinding the back side of a lens.

A special cylindrical lens is needed in order to correct astigmatism. Not only does the strength of the cylindrical lens need to be specified, but the lens itself must be rotated into a specific position in order to provide the proper vision correction. The axis represents the amount of rotation of the cylindrical lens in degrees ranging from 1 to 180.

When the two eyes are not properly aligned and looking directly at the same thing, a prism can be ground into the lenses in order to re-align them. This can occur with strabismus or in situations where the eyes are properly aligned but are under a tremendous amount of strain in order to keep them aligned. The value under the ‘prism’ heading of your prescription denotes the strength of the prism.

The base is to the prism what the axis is to the cylinder. As you know, a prism is shaped like a triangle. The thicker the triangle at its base, the stronger is the power. Much like the axis specifies the direction of rotation of the cylindrical lens for astigmatism, the prism must also be rotated into a specific position. But the rotation of the prism is simply specified as ‘base in’ or ‘base out’ (where ‘in’ means towards the nose) or ‘base up’ or ‘base down’. Only these four positions exist as opposed to the 180 positions that can be specified for a cylindrical lens. However, orientations between these four positions can be specified by using combinations of horizontal and vertical prisms in the same lens.

Our highly skilled opticians help you in selecting the right frame to fit your face comfortably. People usually do not know what to look for in a frame and end up choosing frames that are not appropriate for their prescription or their facial features.

NeoVision’s opticians will also help you in selecting the right lens material (CR-39 plastic, polycarbonate, Trivex, hi index), lens design (single vision, bifocal, trifocal, progressive), and lens coatings (scratch resistance, UV protection, anti-reflective, transitions, polarized) to match your lifestyle.

The optician will measure the precise inter-pupillary distance (PD) to ensure accurate placement of lenses in the frame. PD is the distance from the center of the pupil (black circle) in one eye to the center of the pupil in the other eye. For multifocal lenses (progressive, bifocal, or trifocal), an optician must determine the correct position for the line that divides the distance vision lens from the near vision lens. The optician will mark the demo lenses for the correct position of this line. The height from the bottom of the lens up to the correct position of the lens-dividing line is called “seg-height.” In order to determine the correct seg-height, the optician must fit and adjust the eyeglass frames on the wearer’s face. The seg-height is different for every pair of glasses, and can only be determined after the eyeglasses have been fit to your face by an optician. If your eyeglasses are manufactured without the appropriate measurement of PD and seg-height, they may not function properly for you. Never order eyeglasses without trying the frame on, optician fitting the frame on your face, and taking the measurements.

Eyeglasses ordered under an insurance plan are usually processed by the insurance labs and we do not have much control over it. They usually take 5-10 business days. However, if you order your glasses privately (i.e. without an insurance plan) and you need single vision lenses without any special coatings, your glasses can be made ready in 1-2 days.

We usually promise 5-10 business days to process an eyeglass job. The actual time for a particular pair of eyeglasses depends upon a variety of factors including your prescription and lens options you have chosen. Remember, eyeglasses are a custom-product i.e. they are made to your unique specifications. Occasionally, during the process of lens edging and mounting, the frames or the lenses are damaged and the lab needs to start the order all over again. This can add to the overall time to finish a particular job. Eyeglasses with drill mount lenses (i.e. rimless frames) generally take longer.

At NeoVision, we apply stringent quality control standards on each and every eyeglass order. Our opticians inspect every job after it has already been checked and approved by the manufacturing lab. If we notice any defects in the frame or lenses, we will not deliver it to you. Instead, we reorder the frame or the lenses and process the order all over again. While this could add time to your order, you can be assured that the final product you receive from us will be in a perfect condition. Our emphasis is on the finest quality of the final product rather than rushing an order.

No, if you have plastic lenses in your glasses then dry tissues will scratch them. It is generally better to dampen the tissue, or even use soapy water and a soft cloth. Glasses with anti-reflective coating should be cleaned with a special cloth and spray.

We recommend polycarbonate or high-index lenses in a small frame. Avoid rimless frames.

We recommend polycarbonate or high-index aspheric lenses. Avoid rimless frames.

We highly recommend polycarbonate lenses that are more impact resistant.

Polycarbonate lenses in a flexon frame with spring hinges.

The “standard plastic” lenses are often called “Hard Resin”, “CR-39 plastic”, or just “plastic” lenses. CR-39® is actually a PPG Industries registered trade name for a DADC (diallyl diglycol carbonate) polymer that was introduced in 1941. The “CR” stands for Columbia Resin and CR-39 was the 39th batch or formula made by Columbia Laboratories in Ohio. The “hard resin” or “CR-39 plastic” is a thermoset plastic meaning it cannot be molded or bent when heated. On the other hand, the polycarbonate polymers are thermoplastic which means that the lenses can be formed by melting polycarbonate pellets and injecting them into a mold.

Anti-reflective coating.

Anti-reflective coating.

Lenses with anti-reflective coating. These lenses cut down glare on glasses and improve appearance of your eyes.

Lenses with ultraviolet coating or Transitions lenses

All people, including children, are at risk. People who spend long hours in the sun because of work or recreation, those who have had cataract surgery, individuals who have certain retinal disorders, and those who take certain medications, such as tetracycline, sulfa drugs, birth control pills, diuretics, tranquilizers etc. are at even higher risk.

UV400 means that the lens blocks all lightwaves 400 nanometers and below. 400 nanometers is typically referred to as the point where UV light starts. Anything below 400 nanometers is considered to be in the ultraviolet range.

You need frame adjustment. Also, consider lighter lenses such as hi-index or polycarbonate in a smaller frame.

Wear photogrey, light tint, Transitions lenses, or polarized lenses.

Both are equally effective. It is your preference. Generally, people match the color of transition lenses with the color of the frame.

Polycarbonate lens material is so tough that you can hit it with a hammer and it won’t shatter. Ordinary polarizing lenses are made out of plastic (CR-39) and are not shatter resistant. In addition, polycarbonate lenses absorb harmful UV radiations.

Ask your optician to raise bifocal height or consider using progressive lenses.

You should consider using progressive or trifocal lenses.

Your bifocal power needs to be adjusted. Schedule an eye exam with your eye doctor.

It all depends upon your reading prescription and how much you care about the quality of your reading vision. If your prescription is SAME for both the eyes and there is NO astigmatism, you can use reading glasses off the shelf. Of course, you will be very limited in choice of frame and you will also compromise on the optical quality of lenses.

You can order your own custom reading glasses by choosing any of our eye glass frames and adding reading lenses in your unique prescription. You will be able to order glasses with clear prescription lenses or with tinted prescription sunglass lenses with anti-scratch, anti-UV, and/or anti-reflective coating. You will also have a choice of lens materials such as CR-39 plastic, polycarbonate, Trivex, or hi-index.

Many people underestimate the importance of backup pair of glasses. Under certain situations, it may not be possible to repair or replace glasses within the time you have. Imagine, you are about to leave for a business/pleasure trip or you are already on such a trip and your current glasses break. You will unnecessarily go through a lot of inconvenience and lose precious time. You can also imagine what will happen if a student breaks or misplaces his glasses during the exam period. Always keep an extra pair of glasses for unforeseen emergencies. It is like driving a car with a spare tire.

Clean your lenses daily either in running warm water or with a special lens cleaner. For drying, use a soft cotton cloth or special eyeglass cleaning cloth. When not in use, always store your glasses in their protective case. Never place them face down on their lenses. Always use both hands while putting on or taking off your glasses.

There is evidence that sunlight exposure plays a role in certain eye diseases, such as cataract, macular degeneration, pterygium, and eyelid cancer. It is a good idea to wear sunglasses with protection against ultraviolet light. Patients with or at risk for macular degeneration may also benefit from lenses which block blue wavelengths, such as yellow or amber lenses.

Find a reflective surface and hold your sunglasses so that you can see the surface through one lens. Rotate the glasses to see if the glare increases or decreases. If the glare decreases, then you know your sunglasses are polarized. Alternatively, try to see an object below the surface of the water through your sunglasses. If you can see the object clearly under water, your sunglasses are polarized.

Another simple way to check the polarization of a lens is by holding the lens over the top of a lens that you know is polarized. A liquid crystal display (LCD) or digital watch is polarized. Hold the lens over the watch on a horizontal plane and rotate it. If the lens is polarized, you will notice the watch display appears darker as you rotate the lens above it. If the lens is not polarized, there will be no visual difference as you view the watch through the lens.

Children are at a higher risk from the harmful effects of UV since they generally spend more time outside in the sun. Select sunglasses that suit your child’s active lifestyle. The lenses should be impact resistant i.e. made of polycarbonate.

Sunglasses are used for three main reasons: health, performance, and fashion. A quality pair of sunglasses should provide all three functions. Lenses should be of high optical clarity and protect your eyes from harmful effects of UV radiations so that you are protected from developing early cataracts or pterygium. By reducing intense bright light as well as glare, sunglasses should keep you safe whether you are driving or participating in active sports. If you have sensitive eyes, you may also want your sunglasses to filter out more light. Your glasses should also protect your eyes against powerful damaging impacts.

Your choice in sunglasses will also be influenced by fashion. Wire frames go well with most outfits but tend to be more fragile than plastic frames. Wrap-around frames with large lenses will protect you from ambient and direct light and glare from every angle. Wraparounds stick to your face and are in fashion with the surfing, skating, and snowboarding enthusiasts. How your sunglasses look, ultimately, depends on your face, square and rectilinear glasses look better on round faces, and square faces are well suited to oval frames. Strong, lightweight composite or metal frames are typically used for brand-name sunglasses. The higher-quality sunglasses generally have tension springs connecting the arms to the face. Brand-name sunglasses with polarized polycarbonate lenses are comfortable to wear and do not distort colors.

Schedule an appointment at NeoVision Eye Center by calling 1-510-431-5511.