Eye Care Blog

In modern times we have learned to manufacture glass of a much higher and controllable refractive capacity. Correct refraction is as important as the shape of the lens for the efficacy of an optical aid.

The grinding and polishing of regular curvatures on to transparent media to produce lenses that minify objects has thus been going on for several hundred years but the scientific principles underlying the measurement and accurate reproduction of thin spectacle lenses belong to modern times. Even so, the standardization of ‘best’ lens forms, free from aberration, has yet to be agreed at international levels. Nevertheless, at this time, the technical processes of making glass and plastic spectacle lenses is relatively refined, and is carried out by sophisticated machinery designed and researched by skilled scientists and technicians. Pope Leo X’s glasses would almost certainly have been concocted by a Venetian glassblower.

The negative, minifying spectacle lens, for the correction of short sight, is designed to be worn between 8 and 15 mm in front of the eye. While to a certain extent fashion determines the size of the lens and the curvatures on its back surface, fashion does not take precedence over the quality of the lens’s performance, its weight or its thickness. You may request a large-aperture frame, but if the power required of the lens is too high you will have to make do with smaller frames, though a compromise can sometimes be obtained by reducing the area of optical correction. For seeing well over a large field of vision small-shaped lenses are always more satisfactory, provided they can be fitted reasonably close to the eye. The centre of the lens must always be over the centre of the eye, otherwise a prismatic effect is induced. Such an effect, unless it is specifically required to cope with some eye-muscle defects and certain kinds of squint, causes displacement of the object looked at, resulting in discomfort and even double vision. The change-over from old to new spectacles, even when they are of an identical prescription, is always accompanied by a period of adaptation. One of the causes of headache and eyestrain during a change-over is that the new lenses are almost inevitably centred slightly differently from those previously worn. Therefore you should consult the specialist only if symptoms persist. Generally, any discomfort will go away after a few days as the eye accustoms itself to its new aid.

The spectacle lens is also fitted into a frame that not only holds it at a fixed distance from the eye but also at an angle to the face. This permits comfortable vision when looking down at the floor and elsewhere. It is generally assumed that you will want to look up to the sky less often.

The modern spectacle lens may be made of either glass or plastic. Plastic lenses are made of methacrylate or other lightweight substances. Whilst they are lighter than glass, their refractive power is slightly lower and therefore they need to be thicker. The colour and clarity of the image they give may also differ. In general a plastic lens gives a softer image than glass. Because plastic is less effective at refracting light (bending light rays), its curvatures have to be steeper, and it is therefore particularly thicker at its edges. Both types of lens can be tinted, either by adding dyes or metallic compounds to the basic material before it is cut or moulded, or by coating the surfaces with a fine metallic deposit.

There are several reasons why lenses may be tinted or have their light-transmission capacity reduced. To begin with, spectacle wearers like everybody else need sunglasses when the light is very strong, and to have a pair of corrective spectacles that are also darkened is preferable to plastic ‘clip-ons’. Decrease in light transmission is helpful to patients sensitive to light (and shortsighted people do tend to be light-sensitive) or to patients who have to work in particularly bright conditions. It should be remembered that short-sighted spectacles tend in any case to increase the intensity of light entering the eye, so that sometimes it is necessary to restore the balance. But there are also ways of tinting a lens so that the decrease of light transmission is only selective. Thus green-tinted lenses reduce the amount of white light entering the eye, white light being especially reactive to the central part of the retina. Green tinting also reduces the infrared end of the spectrum and therefore controls the amount of heat passing through the eye. Ultra-violet light is usually screened out, or at any rate screened down, by the density of the lens material, but this is less the case with plastic lenses than with glass lenses. To be effective, sunglasses must cut out ultraviolet light. If they do not, and many cheap sunglasses don’t, they do not offer any real protection.

In certain environments some protection against the more harmful rays of sunlight is essential, even for people with normal sight. These environments occur naturally at sea, in the desert, and where there is snow cover. Failure to provide protection greatly enhances the risk of developing cataract. There are several age-old ethnic customs related to such geographic conditions, sometimes wrongly regarded as merely ornamental. Thus the Moroccan bedouin paint kohl round their eyes, allegedly for protection against the ‘evil eye‘, but in reality

It is completely unusual to have Drop Ship Eyeglasses Lens, Wireless Pinhole Camcorders, Camera Lens Filters Supplier, DVR Sunglasses, DERMALOGICA Soothing Eye Make, Buy NINA RICCI Glide-Off Lotion, Best Eye Makeup Remover, Skin Care Products, Lens Drop Shipping Wholesale, STILA Eye Shadow Stick - # 02 For Sale, Skin Cleansers Drop Shipping, Drop Ship Eyeglasses Care, Wholesale Eye Shadow, Spy Cameras, Eyeglasses Frames Supplier and HELENA RUBINSTEIN All Special drop shipping wholesaler, a useful on-line wholesaler catalogue.

Possibly related posts: (automatically generated)
Spectacles and Contact Lenses

• Correcting the Vision by Implanting Plastic Eye Lens continue...
• How to Read Eyeglass Prescriptions
• Correcting the Vision by Implanting Plastic Eye Lens
• Corneal Degeneration
• Dos and Don’ts Following Eye Cataract Surgery
• Eyeglasses Adjustment after Eye Cataract Operation
• Eye Sight, Short- and Long-Sightedness continued
• Better Eyesight without Eyeglasses, Treatment in Schools: a Method that Succeeded part 2
• Eye-Strain, might need Vision Test
• How to choose Eyeglass Frames that Complement or Contrast with the Shape of your Face