Don't Ignore the Little Secret of Pupillary Distance During buying prescription glasses online.

Pupillary distance is a crucial yet often overlooked factor. Pupillary distance, also known as Papillary Distance (abbreviated as PD), is measured in millimeters (mm). It is divided into monocular pupillary distance and binocular pupillary distance.

Binocular pupillary distance refers to the distance between the center of the right pupil and the center of the left pupil, mainly used for normal people to fit glasses. Monocular pupillary distance is the distance from the center of the right or left pupil to the mid - line of the nose, mainly used for special groups such as single - eyed people, those with manifest strabismus, and those using progressive multifocal lenses.

Many people only focus on the lens power when buying prescription glasses online, but don't realize that the accuracy of pupillary distance is equally important for the wearing experience and eye health.

Generally, the error of monocular pupillary distance should not exceed 0.5mm, and that of binocular pupillary distance should not exceed 1mm when fitting glasses. If the pupillary distance error is > 2mm, problems will occur! The most common one is dizziness.

This is because when the eyes see things through the lenses, the light cannot accurately focus on the retina, and the brain needs to constantly adjust the visual signals, resulting in a dizzy feeling in the head. At the same time, there will be visual fatigue.

The eyes are in a tense state for a long time, making them prone to soreness and pain. Wearing glasses with inaccurate pupillary distance for a long time may even accelerate the increase of myopia.

The Optical Center of Lenses under Correct and Incorrect Pupillary Distances

To give you a more intuitive understanding of the difference between accurate and inaccurate pupillary distances, let's look at the following two comparison pictures. In the first picture, we can clearly see that the optical center of the lens perfectly matches the pupil position.

When we see things through such a lens, the light can directly and smoothly pass through the optical center of the lens and reach the retina unimpeded. It's like a flat and straight highway, where vehicles (light) can travel quickly and stably to the destination (retina).

The eyes can easily and naturally receive clear images without any visual interference, and the wearer will feel extremely comfortable, as if the glasses and the eyes are integrated, hardly noticing its existence. In the second picture, it shows the situation of incorrect pupillary distance. At this time, the optical center of the lens is obviously deviated from the pupil position.

When the light passes through the lens, it's like a vehicle suddenly deviating from the highway during driving and having to take a tortuous and complex path to reach the retina.

This causes the light to refract and not focus accurately, making the objects we see blurry, as if covered by a layer of fog. At the same time, in order to adapt to this mismatch, the eyes need to constantly adjust and focus, just like a vehicle struggling to drive on a bumpy road, which easily causes fatigue.

Staying in this state for a long time will not only make us feel dizzy and extremely uncomfortable when wearing glasses, but may also cause irreversible damage to our vision, just like a vehicle driving on poor road conditions for a long time, whose parts will wear out faster.

Revealing the Industry Secrets: The "Traps" behind Low - price Packages

In this highly competitive online glasses - fitting market, some unscrupulous merchants often use various "tricks" to pursue high profits, making consumers defenseless. Among them, "low - price packages" are one of their most commonly used means.

For example, a certain platform launched a "99 - all - inclusive package". At first glance, the price is so low that it's tempting, as if you've found a great deal. But you may not expect that there is a huge "trap" hidden behind this seemingly affordable package. After investigation, it was found that the lenses used in this package are actually recycled resin lenses.

The sources of these recycled resin lenses are complex. They may be recycled from various discarded glasses. After long - term use and wear, their optical properties have already been greatly reduced.

To let you understand the harm of recycled resin lenses more clearly, let's look at a set of experimental data on material light transmittance. The light transmittance of normal new resin lenses can generally reach over 90%. Light can smoothly pass through the lenses, allowing us to see a clear and bright world. But for recycled resin lenses, due to scratches, wear on the surface, and changes in the internal structure, the light transmittance drops significantly, maybe only around 70%. This means that a large amount of light is blocked and scattered when passing through the lenses, making the objects we see blurry and dim, and the visual effect is greatly reduced.

Wearing such lenses for a long time, the eyes need to work harder to obtain a clear image, which undoubtedly increases the burden on the eyes and easily causes problems such as visual fatigue and dry eyes, seriously affecting eye health. In addition to low light transmittance, the other properties of recycled resin lenses are also not guaranteed.

For example, its scratch - resistance is weaker, and it is more likely to have more scratches in daily use, further reducing the light transmittance. Moreover, its UV - resistance may also be insufficient, unable to effectively block the damage of UV rays to the eyes.

Wearing them for a long time increases the risk of various eye diseases. Therefore, when choosing an online glasses - fitting package, never just look at the price. Be cautious and avoid falling into these "low - price traps".

Precautions for buying prescription glasses online

When buying prescription glasses online, there are many key points we need to pay attention to. Choosing a regular platform is the crucial first step.

Platforms like Glasses Magic, which have a good reputation and high credibility, can not only provide a wide variety of product choices but also give strong guarantees in terms of quality and after - sales service, allowing us to shop without worries.

Understanding the characteristics of lens and frame materials is also important. For lenses, the common types are resin lenses, glass lenses, and PC lenses. Resin lenses are lightweight, not easy to break, and have good impact resistance, so they are the first choice for most people.

Glass lenses have excellent optical properties, high light transmittance, and clear vision, but they are relatively heavy and fragile. PC lenses are ultra - light and have strong impact resistance, especially suitable for sports enthusiasts. For frame materials, each has its own advantages.

Pure titanium frames are lightweight, corrosion - resistant, and less likely to cause allergies, but they are relatively expensive. β - titanium frames have strong plasticity, a variety of styles, and high cost - performance.

Alloy frames are affordable and have rich styles, but they may be prone to corrosion and rust, and some people may be allergic to them. Acetate frames have a strong texture and are wear - resistant, suitable for people allergic to metals, but the material is relatively hard and heavy. We can choose the appropriate materials according to our needs, budget, and wearing habits.

Checking user reviews is also a practical tip. Through the real feedback of other consumers, we can more comprehensively understand the advantages and disadvantages of products, such as the clarity of the lenses, the comfort of the frames, and the fineness of the workmanship, so as to avoid buying products of poor quality.

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