Diopters Explained

The optical power of a lens with a focal length of 1 meter (about 39 inches) is said to be 1 diopter. Because the formula is based on the reciprocal of the focal length, a 2 diopter lens is not 2 meters but 1/2 meter, a 3 diopter lens is 1/3 meter and so forth. This is important because magnification increases as the focal length gets shorter, which is why a prescription for a higher diopter correction means you need more magnification.

The optical power of the human eye is about 40 diopters. The eye of a normal young person can adjust an additional 20 diopters. By age 25 this accommodation is usually reduced to about 10 diopters and by age 50 to a mere 1 diopter. It is this diminishing capacity for adjustment, called presbyopia, that warrants reading glasses.

Reading glasses compensate for the loss of natural adjustment. Optical power is additive so the correction is straightforward. An optometrist prescribes a lens that increases the magnifying power of the eye, usually in steps of a quarter-diopter over a range of 1 to 3 diopters. A quarter-diopter is a large enough step that most people can self-prescribe their own reading glasses by simple trial and error.

The level of magnification in the lenses of reading glasses is called diopter strength. A very weak magnification would be found in reading glasses with a diopter strength of +.75 or +1.00. Off-the-shelf reading glasses sold in drug stores or elsewhere on the Internet are often offered in diopter strengths that start with 1.50, and with only a few options for stronger lenses.

We do not sell pre-fabricated glasses. Instead, each pair of our glasses is custom fitted by a certified optician. Generally, the eye care industry classifies reading glasses lenses in diopter strengths that increase by a factor of .25 (e.g., +.75; +1.00: +1.25; +1.50; +1.75; +2.00; +2.25; +2.50; +2.75; +3.00 etc.).

Presbyopia sometimes effects your left eye and your right eye differently. Therefore, you may need, for example, a +1.50 in your right eye and a +1.75 in your left eye. This is normal, although many people can overcome their Presbyopia perfectly by using glasses that have the same diopter strength in each eye. Nevertheless, if you fall in the category of people who need differing lens strengths for each eye, you could be doing yourself a grave dis-service if you bought a cheap pair of one-size-fits-all drug store glasses that had the same diopter strength in both lenses. Those are also the kind of stock reading glasses sold on most of the other Internet sites.

We believe we offer you an extremely valuable option in that we can easily accomodate you if you need a different lens for each eye.

Presbyopia is progressive, and therefore, the strength of magnification in your reading glasses will probably have to be increased every year or two. Moreover, depending on what else is going on with your body, you may find that your need for stronger and weaker lens strengths can fluctuate slightly during any given period. In fact, you may need a stronger lens strength to eliminate the blur when you read your newspaper in the morning than what you would need to read the same newspaper in mid-day. That is why some experienced users of reading glasses have more than one pair, each with slightly different diopter strengths. According to these experienced users, whether you would find greater comfort with more than one pair is something best determined through trial and error.

Reading glasses are available without a prescription, and are intended as an aid if you have blurred vision at close distances. It is your right to self prescribe your own glasses, and if you do so, you will not be violating any law or regulation. In fact millions of people just like you have determined for themselves what strength glasses they needed, and then bought them without ever consulting a doctor or other licensed professional. The easiest way to find out the diopter strength you need is to visit a drug store, department store or other retail outlet that sells cheap reading glasses, and try on a few different strengths.

If you have no idea where to start, consider using this average age formula: If you are under 40 years old, you probably should start with a +1.25 strength. Between ages 40 and 45, you probably need +1.75. At ages 45 to 50, you probably need +2.00. After age 50, you probably need +2.25.

While this is based on averages, and you should try to find the precise lens that helps you, the nice thing about buying FOCUSERS is that if you make a mistake, you can quickly and at no risk to you, rectify it under our RETURN POLICY and NO EXTRA COST EXCHANGE POLICY.

In addition to the methods mentioned, you can always visit an optometrist or ophthalmologist to have your eyes refracted.

Additionally, reading glasses can be safely, self-prescribed by you, the user, with the aid of a simple eye chart.