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Lens Selection

Help Selecting Lenses

The top priority of the Carytown Optical online store is to make certain that your lenses are done correctly and you experience natural vision. We offer only the highest quality lenses made by the world's leaders in ophthalmic lenses. Eyeglass lenses correct refractive errors within the eyes. When choosing lenses keep in mind that the higher the refractive index, the thinner the lens. The lens power that you need to ensure high-quality vision is indicated on the eyeglass prescription from your eye doctor. The lens power to correct refractive errors in the eyes is measured in diopters (D). If you are nearsighted the value is negative (thinner in the center and thicker at the edge) and farsighted it is positive (thicker in the center and thinner at the edge).

If you want thinner and lighter lenses that are attractive and comfortable choose high-index eyeglass lenses. High-index lenses (lens material with a refractive index that's higher than that of glass i.e. 1.523) are particularly suggested if you have a strong eyeglass prescription for astigmatism, farsightedness or nearsightedness. The stronger the prescription for nearsightedness the thicker the lens edges as mentioned before. The edges of the lens are most visible, and when thick, can detract from the look of your eyewear. With trendy frames made of plastic and metal, the rim is thinner than the lens and with popular rimless frames the lens edges are completely exposed.

Some of our lenses come standard with UV400 protection which gives a high level of protection. Your lens will block 100% of all harmful ultra violet light from the sun (These lenses block light rays with wavelengths up to 400 nanometers, so your eyes are shielded from even the tiniest UV rays.)

Additional guidelines for choosing lenses are provided below.


Decide if you want a prescription or non-prescription lens. If you choose prescription lenses you need to select the prescription strength (Low Prescription (< +/- 2 spherical power), Medium Prescription (Between +/- 2-4 spherical power) and High Prescription (> +/- 4 spherical power). It is critical that you choose the proper category since that determines what lens material and lens options will be available to you.


Please select between Sun/Transition or Clear lenses.


Depending on your prescription you can select lens material as follows:

  • Non Prescription Lenses - Plastic Lenses, Polycarbonate Lenses & Trivex Lenses
  • Low Prescription Lenses - Plastic Lenses, Polycarbonate Lenses & Trivex Lenses
  • Medium Prescription Lenses - Polycarbonate Lenses, Trivex Lenses and High Index 1.67 Lenses
  • High Prescription Lenses - Trivex Lenses, High Index 1.67 Lenses & High Index 1.74 Lenses
Plastic Lenses - CR39, with Scratch Resistant Coating

CR-39 lenses (plastic lenses) are relatively safe, have a low cost, are easy to produce, and also provide excellent optics and vision correction. Plastic lenses are half the weight of traditional glass lenses, which makes them more comfortable. To overcome the softer lens surface, scratch resistant coatings are included on all our plastic lenses. Plastic Lens or CR-39 has a refractive index of 1.498.

Poly Lenses - Thin polycarbonate lens with UV400 and Scratch Resistant Coating

Polycarbonate Lenses have a refractive index of 1.58 and are the most durable of all lenses and the safest, lightest and thinnest available. They are made of a virtually unbreakable polycarbonate material that automatically filters harmful UV rays. This allows the material to be ground very thin in the center for minus or nearsighted prescriptions which allows for much thinner lens edges. These lenses have the highest impact resistance therefore, making them great for kids, playing sports and safety glasses. Polycarbonate is an excellent choice for rimless eyeglasses.

Trivex Lenses

Trivex Lenses have a refractive index of 1.53 and are ultra-lightweight and much more impact-resistant than regular plastic or glass lenses. It is composed of a urethane-based monomer and manufactured within cast molding process (as regular plastic lenses) and ideal for drill mount frames (rimless frames). It offers similar UV blocking properties and shatter resistance as polycarbonate lenses. Trivex lenses can be easily tinted. Polycarbonate is thinner but Trivex lenses are lighter than polycarbonate lenses. Trivex lenses have less internal stress and a higher Abbe value (V-number or constringency) and may result in sharper central and peripheral vision with less chromatic aberration than polycarbonate lenses.

High Index 1.67 Lenses - Scratch Resistant and UV400 protection

The High Index 1.67 Lenses are made from special plastic material that refracts light in a different way than regular plastic. This material is also thinner and lighter weight than regular plastic lenses and although it is a strong material it is not unbreakable and not as shatter resistant as polycarbonate. This material is great for higher prescriptions and is often recommended by doctors for its optical quality and also suitable for rimless eyeglasses. The bottom line is that thin eyeglass lenses are more comfortable and attractive than thick ones.

High Index 1.74 Lenses - Scratch Resistant and UV400 protection

High Index 1.74 Lenses is approximately 15% thinner than High Index 1.67 which makes it approximately 50% thinner than conventional plastic in most RX (prescription) ranges. High Index 1.74 lenses are also scratch resistant and UV400 coated and most suitable for higher prescriptions. (NOTE: You must order Crizal Advance or Crizal Sapphire when ordering this lens. 1.74 Lenses are not made without anti -glare)


Solid Lens Tinting & Ultra Violet Filter

UV Protection shields your eyes from sun rays that can be damage your eyes. Solid Lens Tinting adds tint to your lens and are available in different colors. Although tints could be purely cosmetic we provide it as a sunglass tint. The percentage of color refers to the amount of color in the lens and the higher the percentage the darker the lens. The lens tint that we recommend and provide is 80%. This is a sunglass tint. Please provide additional instructions if you need a lighter tint.

Transition Lenses - Light Changing Lenses

Transitions lenses are used as an adaptive lens technology that is sensitive to ultraviolet light causing the lenses to lighten to completely clear indoors, and within minutes darken to a sun tint outdoors in direct sunlight. Right in any light. The #1 photochromic lenses recommended by eye doctors. Transitions Lenses block out 100% UV radiation and reduce glare. Transition lenses are dependent on the ultra violet rays of the sun to activate them. For this reason, they do not darken inside of the car and they will darken on overcast or cloudy days. The brighter the sun, the darker they get, getting as dark as sunglasses in bright light.

Polarized Lenses – Ultra Lite Style Sun Lenses

You'll be amazed at how much better your vision can be through polarized lenses which is better than natural human vision. In layman's terms, a polarized lens in like having a mini venetian blind built into your lens. It organizes the light which is bombarding your sight from all angles. The polarization only allows light in at one angle or plane. This eliminates glare. They are great for anyone who spends their time outdoors; Golf, tennis, skiing, jogging, biking, boating or fishing. They are also great for everyday life such as driving. This is why fisherman can see beneath the surface of the water. Once you try them you'll never go back! Polarization also blocks 100% of harmful UV rays. Pilots do not wear polarized lenses as well as mountain bikers or anyone dependent on reading gauges.


Premium AR Coating for Plastic, Polycarbonate, Trivex and High Index 1.67 Lenses

Anti-reflective treatment is applied to front and back surface. This treatment is the perfect companion for high-index lenses. All lens materials block some light from passing through that is reflected from the lens surface causing distractions and reducing vision clarity. AR-coated on high-index lenses eliminate lens reflections and transmit up to 99.5 percent of light to the eye for optimum vision. Anti-reflective coating has a real advantage for night drivers since it provides sharper night vision with less glare. Anti-glare is also great cosmetically giving the lenses an invisible appearance. In general, your experience will be that your eyes are less tired, especially with extended computer use, your eyes will not be hidden by glare and your lenses will have a much tougher scratch resistant surface. We recommend AR Coating with every prescription.

UV Protection Coating for Plastic Lenses (Not needed if you select Blue Light Protection)

UV Protection is a treatment applied to a lens to protect the eyes from the exposure to harmful UV rays. This is a coating that filters out 100% of the damaging ultraviolet (UVA/UVB) rays of the sun which are known to cause damage to the macula and the intraocular lens of the eye. The UV400 coating is colorless. Consider it a permanent sun block lotion for your lenses. This extra treatment is not necessary on all lens materials since certain lens materials already block harmful UV rays as discussed below.

Crizal Advance Coating for all lenses

Crizal Advance with Scotch Guard gives you everything you've ever wanted from your lenses:

  • Provides the best possible cosmetic appearance for your lenses by preventing reflections and allowing others to see your eyes completely clear.
  • Creates clear vision by helping the maximum amount of light to enter your eyes as well as eliminating back side lens reflections such as seeing the reflection of your own eye or eyelashes.
  • Prevents the reflections that cause eyestrain and fatigue.
  • Incredibly easy to clean, greater smudge and dirt resistance. It is fused into the lens material making it extremely durable.
  • Provides unbeatable two-sided scratch resistance.
Crizal Sapphire for all lenses

Crizal Sapphire is the best Anti-Reflective Coating available today and is fused into the lens material for a diamond-hard protection which won't peel or lift off of the lens like many lower quality reflection free coatings. This scratch resistant coating provides the sharpest vision of any no-glare lens available on the market. Crizal Sapphire virtually eliminates reflections from headlights, taillights and other light sources which allow drivers to make faster adjustments to changing conditions. Crizal Sapphire has a distinct blue appearance to the lens. The Crizal Advance is less noticeable on the lens surface

NOTE: You must order Crizal Advance or Crizal Sapphire when ordering High Index 1.74 lenses.

Blue Clear lens (Blue Light Protection) for Plastic, Polycarbonate and High Index 1.67 Lenses

Blue Light Protection reduces harmful blue-violet light exposure from computers and other digital devices. Blue light is now believed to play a significant role in the onset of Age Related Macular degeneration. The Blue Clear Lens can prevent this as well as headaches, fatigue and blurred vision associated with digital eye strain. Blue Clear provides:

  • Blue-Violet light protection.
  • Clear and comfortable vision.
  • Reduces glare.
  • Resists scratches and smudges.
  • Repels dust and water.
  • Blue Clear Blocks Blue Violet light which interrupts the production of melatonin thus allowing for a more restful sleep and help eliminating insomnia. 
  • Blue Clear lenses are not available in transition
Crizal Sun Coating (Crizal SunShield) for Solid Tint and Polarized Lenses)

Crizal SunShield offers improved UV protection by incorporating a new optimized formulation to eliminate backside reflections (allowing 30 percent less UV light into the eye than ordinary sun lenses). It helps protect the wearer from UV- related diseases, such as macular degeneration, cataracts and pterygium. In addition, Crizal SunShield lenses eliminate 99 percent of visible glare and light reflections on the back side of the lens, which makes vision more comfortable, especially in sunny conditions. Crizal SunShield lenses incorporate the advanced technologies of Crizal Advance™ lenses with Scotchgard™ Protector, the SR BoosterTM Layer and anti-static properties to the back side of the lens to enhance scratch protection and resistance to dust and water.


Polished Lens Edges

Polished lens edges simply look better because they are clear and therefore less noticeable. Lens edge polishing is a cosmetic treatment that transforms the lens edge from a cloudy, frosted look to a crystal clear shine making lenses appear thinner. An edge polish is most effective with high prescriptions and is available for all lens materials and designs. Polished lens edges give your eyewear a more finished look; but they are recommended most in Rimless, semi rimless and metal frames. In plastic frames polished edges can tend to reflect light and a satin edge polish is recommended. Please notify us with your order if you prefer that.

STEP 5 - PROVIDE PD & PRESCRIPTION (Required if you order prescription lenses)

Provide Pupillary Distance (PD)

Pupillary Distance (PD) or inter-pupillary distance (IPD) is the distance (the industry standard is to measure in millimeters) between the centers of the pupils in each eye. A typical PD value is between 46 and 74. It is needed to ensure the center of each lens is aligned with the center of your pupils. Positioning lenses correctly in relation to the center of the pupils is especially important for higher powered lenses due to the location of the optical center of the lenses. We would need your PD before we can place your order for prescription lenses. This is NOT part of your prescription and should be preferably obtained from your optician. If you do not have it now, please email that to us ASAP.

How will you send us your prescription?

Please select:


For the curious
  •  Sphere (SPH) - The sphere refers to the amount and type of prescription you require. Short-sight is corrected by negative (-) sphere values, long sight by positive (+). If the sphere value for one eye is negative, then the other is usually also negative and vice versa. If you only see one number for each eye on your prescription, it's the "SPHERE" power. It is common for the doctor to leave out the decimal points. A number like -25 or +175 is the same as -0.25 or +1.75, respectively.
  • Cylinder (CYL) - The cylinder is only relevant if you have an astigmatism (or visual distortion). This value determines the strength of the astigmatism correction. If the cylinder value for one eye is negative, then the other is usually also negative and vice versa. Prescriptions can be written in + cylinder construction (ophthalmologists write it this way) or - cylinder construction (the rest of the optical world writes in).
  • Axis (AXI) - The axis value is the angle of the astigmatism correction. If you have a cylinder reading on your prescription then you should have an axis reading. An axis of 5 (or 05) is the same as 005; 90 are the same as 090. 
  • Reading Addition (ADD) - The addition value is the amount of additional correction to add to the sphere value for reading or intermediate glasses. If you only see one ADD power, it's understood that you have the same ADD for both eyes.
  •  Pupillary Distance (PD) - Your Pupillary distance (PD) is the distance, in millimeters, from one pupil to the other. A correct PD will ensure that the lens optical center (the point at which light enters the lens undistorted) is placed directly at your pupil. PD measurements are often taken individually for each eye.

More on Abbreviations and Terms

Similar to eyeglass prescriptions frequently contain a number of different abbreviations and terms:

  • DV is an abbreviation for distance vision. This specifies the part of the prescription designed primarily to improve far vision. In a bifocal lens, this generally indicates what is to be placed in the top segment.
  • NV is an abbreviation for near vision. This may represent a single-vision lens prescription to improve near work, or the reading portion of a bifocal lens. Some prescription forms use ADD in place of NV with a single box to indicate the additional refractive power to be added to the spherical of each eye.
  • OD is an abbreviation for oculus dexter, Latin for right eye from the patient's point of view. Oculus means eye. 
  • OS is an abbreviation for oculus sinister, Latin for left eye from the patient's point of view.
  • OU is an abbreviation for oculi uterque, Latin for both eyes.
  • spherical correction corrects refractive error of the eye with a single convergent or divergent refractive power in all meridians.
  • cylindrical correction corrects astigmatic refractive error of the eye by adding or subtracting power cylindrically in a meridian specified by the prescribed axis. 
  • The axis indicates the angle in degrees of one of two major meridians the prescribed cylindrical power is in. Which major meridian is referenced is indicated by the cylindrical correction being in plus or minus notation. The axis is measured on an imaginary semicircle with a horizontal baseline that starts with zero degrees in the 3 o'clock (or east) direction, and increases to 180 degrees in a counterclockwise direction.