The logical place to start is with lens materials and designs. Every ophthalmic lens material has three physical properties that will dictate how the lens will work. These properties are:
- Specific gravity
- Reference index of refraction
- Abbe number
The specific gravity of a lens material is a measurement of density or weight of a particular material. A material with a lower specific gravity will be lighter than another material with a high specific gravity. This is why plastic lenses are lighter than glass lenses.
The refractive index measures the effect a material has on the bending of light as it passes through it. A higher index will have a greater effect on light and less lens thickness is required to produce the desired prescription. This will result in thinner and lighter lenses than a lens material with a low index.
The Abbe number is a measure of the effect the lens has on separating light into colors. A lens with a high Abbe value will not cause color fringes and distortion of light. A low Abbe value means that your vision will not be as sharp.
Therefore, if you would like to design a lens that provides the clearest vision with the least amount of material and weight you should pick a lens with a low specific gravity and a high reference index and Abbe number. Currently all the lens materials can be separated into four categories:
- High Index Plastic
- Ophthalmic Lens Types
The hardest-to-scratch material available today but also the heaviest and easiest to chip or break. It is the least impact resistant.
Polymer “Plastic” Conventional hard resin lenses are half the weight of glass lenses and can be tinted to almost any color and intensity.
This is the most impact resistant of all materials currently available. It is also the thinnest and lightest of all materials. However, it does have the drawback of having the greatest distortion or optical aberrations of any material.
High Index Plastic
Modern technology has created the improved lenses that bend light differently so that stronger corrections are thinner than when made with conventional plastic materials. In general, high-index plastic lenses will most closely meet the goal of lightweight, thin, and optically-clear lenses. In addition to choosing the material, it is often more important as far as how the lens is ground. For high prescription lenses, it is best to use an aspheric design. An aspheric lens design will provide better cosmetic appearance, while preserving or enhancing good vision. Each lens material has its advantage and you should discuss your lifestyle and visual needs with your optometrist. Often a specific lens for occupational, sport, or computer use provides the best option.
Ophthalmic Lens Types
- Single Vision Lenses: When correction is needed for only one distance, or when only one power is needed to see clearly at all distances, a single vision lens is most appropriate.
- Progressive Lenses: When you need a different prescription for reading than for distance, a progressive lens offers the benefits of a multifocal lens (with gradually changing power) without lines between powers. These lenses provide more natural vision by allowing clear sight at all distances (distance, near, and everywhere in between). They are available in all materials.
- Bifocals Lenses: Bifocals provide correction in two powers – distance & near. As the need for a reading lens progresses to stronger powers, a bifocal is no longer able to adequately provide clear intermediate vision. A gap develops between the distance and near clear zones causing blurred vision at arm’s length.
- Trifocal lenses: Trifocals provide correction for three powers- distance, arm’s length, & near. This can provide limited correction for the gap left by a bifocal when higher correction powers are needed for reading. While not as continuous as a progressive lens design, a trifocal does provide clarity beyond the reading distance out to approximately three feet.
- Computer Lenses: Extensive computer use requires correction for the computer distance in the straight position of the lens (so you do not have to tilt back, extend and stress your neck in order to see clearly at that working distance). Computer lenses are designed to provide computer correction in the middle of the lens with reading below and distance correction in the upper portion of the lens so you can look up and see clearly across the room.
- Occupational Lenses: Occupational designs are available to meet the special needs presented by certain work environments. Many occupations require extensive near work both below and above eye level (carpenters, mechanics, plumbers, electricians, etc.). Specially-designed lenses can provide near correction in both the top and bottom portion of the lens.
- Sports Glasses: Many lens designs and lens treatments are available for the special requirements of sports enthusiasts. From swim goggles to ski goggles, fishing lenses to shooting and mountain climbing lenses, they are designed to help you get the most out of your endeavors with visual efficiency, comfort, and safety. Polycarbonate is the material of choice for active sports. For more information on types of sunglasses available, please visit the Oakley Sunglasses Website.
- Polarized Sun Lenses: Polarized lenses eliminate reflected glare from surfaces illuminated by bright sunlight. They are great for driving, fishing, hunting, and all types of outdoor activities.
These are by no means the only lens materials, designs, or treatments available. Please tell us your work or leisure visual interests and we can tailor exactly the right lenses for all your visual needs.
Contact us today at (405) 372-1715.