Simple explanations of optical related terminology to make choosing your reading glasses easier.
As light passes through a lens, a percentage of it is reflected back off the surface of the lens, rather than being passed through the lens. These reflections cause glare which can make reading strained and exhausting. An anti-reflective coating reduces surface reflections resulting in clearer, more comfortable vision with reduced eye strain for long periods of close work. High quality coatings are essential to holding up to all day, everyday wear. Anti-reflective coatings are best cleaned with a microfiber cloth (included with your purchase).
Aspheric reading glasses lenses are made with flatter curves than standard ophthalmic lenses, giving them a slimmer, more attractive appearance. Aspheric lenses have a more complex front surface that gradually changes in curvature from the center of the lens out to the lens edge. Reading glasses made from aspheric lens create a wider field of view and better peripheral vision. This means that as your eyes move to read your vision will be consistently clear and comfortable. Aspheric lenses also minimize the magnified appearance of your eyes behind the lens which is especially obvious in higher lens strengths.
Astigmatism describes how the eyes focus light; it’s not a disease or eye health problem. Light that does not to come to a single focus on the retina, the central part of the back of your eye that sends visual stimulation to your brain to produce visual images instead, has multiple focus points that occur, either in front of the retina or behind it or sometimes both. Over the counter reading glasses do not correct for astigmatism but for many people they correct them quite well. This is very subjective and is usually affected by how much astigmatism you have.
The bridge measurement is the minimum horizontal distance between the nasal lens parts of the frame's lenses. It's measured from lens to lens from the inside of the rim of your frame. Metal frames come with adjustable nose pads attached to the bridge so that they can be narrowed or widened to suit a variety of nose sizes. In a plastic frame, the bridge width is fixed. A too tight bridge will pinch at the nose and cause the frame to sit too high, while a too large bridge may cause your glasses to sit lower on your nose or slide down to an awkward position. Usually, reading glasses necessitate a wide bridge for easy positioning of your readers lower or higher on your nose.
Cellulose acetate is a natural plastic, which is manufactured from purified natural cellulose. Natural cellulose in the appropriate mix is derived from two basic sources, cotton linters and wood pulp. It is hypoallergenic and known for being strong, lightweight, and flexible. Cellulose acetate can also be made up in a wide range of colors and finishes. For eyewear, cellulose acetate is used by forming layers of plastic into large blocks then carefully dividing it into individual parts, hand polishing and finally assembling them into a frame. Done properly, this is an extremely labor-intensive process that takes several months.
COMPUTER READING GLASSES
Computer reading glasses are reading glasses whose lens strength is determined by the distance you view your computer screen and are used specifically for reading at that distance. Traditionally reading glasses meant book reading distance which is typically 14-16 inches.
COMPUTER EYE STRAIN
Known as that tired, strained feeling, computer eye strain or as it is technically called, Computer Vision Syndrome (CVS), has become more commonplace today as we spend hours, day after day in front of the computer. CVS is usually characterized by fatigue, redness, irritation, burning or dryness and even double or blurred vision. Many of the symptoms can be alleviated by making adjustments to your work environment, optimizing computer monitor settings, and using reading glasses for computer distance rather than the typical book reading distance.
A diopter is a unit of measurement of the optical power of a lens. Corrective vision lenses are measured in diopters.
This measures the entire horizontal width of the frame from the furthest point on either side of the frame.
Hydrophobic coated reading glasses keep clean longer. The coating repels deposits from handling and daily use resulting in clearer vision and easier maintenance. Hydrophobic coatings are usually also oleophobic as well which helps repels oils and other related deposits.
This is the horizontal measurement of one of frames lenses at its widest point measured from inside the lens frame area. The lens width is also referred to as your “eye size”.
Lens dept or lens height is the vertical height of one lens from the inside of the frame.
Optical power is the strength to which a lens or other optical system converges or diverges light. Optical strength is inversely related to optical power which means as you decrease the distance at which you hold your reading material you need to increase your lens power. The eye natural optical power diminishes after age 40 so optical lenses that compensate for that loss of power is used in reading glasses.
Optical quality lenses are made from high-quality plastics that meet specific ophthalmic standards. Free of waves, imperfections and providing true visual clarity, optical quality lenses allow you to see clearly effortlessly. Optical quality lenses are made from premium plastic ophthalmic lens material such as CR-39 or polycarbonate- not acrylic. Optical quality frames are made from superior materials in a long, labor intensive process unlike injection molded frames. Optical quality frames are the same as those used for prescription eyewear and are suitable for prescription lenses.
These are very specific principles and tolerances ( ANSI) that opticians follow to ensure that your glasses are made properly.
Photochromatic lenses are activated by UV exposure and will automatically darken and regulate to light exposure as well as return to its clear state when removed from its activating environment. So whether you're outdoors and it's bright with glare or overcast and cloudy or you want to move inside; reading will be comfortable and easy with one pair that covers all uses.
This term describes the condition where as part of normal aging, the eyes lose their ability to focus close up. This usually becomes noticeable around age 40. The muscles in the eye slowly lose their elasticity, which makes it difficult to see clearly at different distances. This becomes most noticeable when reading small print especially in low light conditions or when reading for long periods of time.
PUPILLARY DISTANCE (PD)
This is the distance, measured in millimeters between the centers of the pupils in each eye. Pupillary distance is the measurement your optician takes to make sure that the center of the lens, which is also the point where you have the clearest vision, lines up with the center of your eye. It should be taken for your distance correction and separately for your reading/near correction since your eyes converge when you read. This simple measurement is important and especially important as the lens strength increases. In ready-made reading glasses whose P.D. is pre-set, some people who need high lens strengths (above a 3.00) may feel uncomfortable reading. As your lens power increases, individual measurements are best followed. Ready-made readers are good but not for long periods of time.
Scratch resistant coatings are routinely added to all types of plastic lens materials which by nature have a fairly soft surface. They are manufactured with a scratch resistant coating to harden their surface and make them more scratch resistant. No lenses are scratch proof; using a micro-fiber cloth to clean them rather than a tissue or paper towel, storing them in their case when not in use and placing those with their lenses face up will reduce scratching.
This is the measurement in millimeters of the frame’s side pieces that extend over your ears. For a comfortable fit, the temples should extend over your ears with a slight curl around the back of your ear to so as to keep your glasses in place.
Lens materials such as polycarbonate and high index plastics have specific properties that inherently protect you from UV. Specific lens technology such as that found in photochromatic lenses also adds UV protection. Simple plastic lenses (CR-39) do not have any UV protection.