OPTICAL CORRECTION

  Organic Lenses

The plastic lenses can have different refractions indexes in order to obtain thinner lenses, higher is the index, thinner is the lenses.

The thickness can be reduced further by an aspherical surface , and by a pre-calibration of the lenses in respect of the distance between the eyes and the frame chosen. These thickness factors can be cumulated , to obtain the minimum thickness in respect to the optical power of the lenses.

SeeMax Bi-aspheric- Multi-direction

The plastic lenses are very light , and are nearly unbreakable , but they scratch easily . We have anti -scratch coatings . The plastic lenses can be tinted in every colors you like, even with different colors in the same lens, and also with progressive shade .

The latest images describes différent gost images.

The link between reflection and the value of the refractive index of the lens is well known. High index glass materials are denser and, for moderate lens powers, generally heavier. (Although for very high powers, glass lens curves reduce and the net effect can be a weight reduction.) This does not happen with plastic materials where the penalty for increasing refractive index is not normally to increase the density, but to reduce the scratch resistance. This can be solved with anti-scratch coatings, which should always be applied to high index plastics. With the growth in sales of high index plastics, it is logical that AR sales should increase in proportion. As high index grows, so AR coating should be encouraged in tandem with it.

As the range of available lens materials increases, so does the complexity of coating. Faced with many different lens materials, the laboratories have the option of optimising their process for each different material, with the consequence of smaller batch quantities, lower production efficiencies and longer production delays. AR coating machinery suppliers have certainly noticed this trend, as even the large laboratories prefer to have a number of small coating machines instead of a few large machines.This problem is even greater for sub-contract coating companies, which are faced with an even larger variety of lens materials from a number of different suppliers.At least the major internationals, who only coat their own lenses, have a restricted range of materials and are also certain that they know the source and type of each lens.

CORRECTION IN COLOR:
Can colour really make a difference to our visual well being ? Apparently so, if strictly controlled clinical trials of coloured lenses are to believed. Mark Ronan speaks to Jenni Brown an optometriste at Rayner Opticians (a UK optical chain) and a council member and examiner for the college of optometry, who specializes in colormetry, a technique that uses the therapeutic effects of coloured lenses to alleviate various perceptual disorders.
Colorimetry is a relatively recent field, but coloured overlays or filters were actually first proposed back in the 1930s to treat visual disorders. In the mid-8Os, an American psychologist, Helen Irlen, fascinated by the findings of a medical conference on the applications of colour, decided to put coloured lenses to the test on children with learning difficulties; she found that colours improved their reading skills. In the UK, Irlen developed her findings and trained special-needs teachers to screen potentially dyslexic children with coloured overlays.

I first came across the theory when my son told me that one of his teachers had suggested that coloured lenses might help this reading problem. I decided to attend some talks on the subject, and I realized that colour therapy was more than just a gimmick. Then I met Arnold Wilkins of the Medical Research Council who was presenting his research on treating photosensitive migraine and epilepsy and learning difficulties with colour overlays.

The MRC agreed to go ahead with clinical trials to corroborate his research and he asked me if I would like to take part. The trials were to establish to what extent colour therapy could be effective in treating a range of problems. As a result, Jenni became involved in the very first clinical research into colorimetry; the trials were carried out on groups of dyslexic children in Leeds and London.
Arnold Wilkins helped to devise the colorimeter, a machine to aid diagnosis by producing different wavelengths of colour. With the machine, you can ascertain which colour and which depth of colour helps alleviate reading disorders.

The patient looks at a target, a word that is designed to be distorted and difficult to read, and the operator changes the colour wavelengths until they isolate a colour that most helps the patient read the target. A lot depends on the individual as to which colours can help. The clever thing is that you can alter the colour and its depth independently until you home in on the colour range and density most comfortable for the subject. You then match the selected colour to the lenses. A significant number of those filtered with tinted lenses find that their reading ability is improved. But why does something as simple as colour actually have this effect on vision.

This is not as easy to answer and different theories exist. Some researchers, including Dr Stein, an 0xford University psychologist, think that dyslexia may involve an abnormality that slows down one of the two major visual pathways - magnocellular and parvocellular - in the brain, so that the visual information is not received in the right sequence. In reading light strikes photoreceptors in the retina; the information is then processed by the magno cells and parvo cells in the brain. In a study of dyslexics, the magno cells were found to be smaller than normal, as was low-contrast processing.

Another theory suggests that the brain's visual cortex, which processes messages from the eye, could be confused by excess electrical activity. It has been found that reading through various blue filters of differing shades helps 80% of the children read better, but exactly how the tints help remains a mystery.
The problem is that it's impossible to measure accurately this specific activity in the brain because it's a huge mass of electrical activity. It seems likely that tints damp down some of the electrical activity that interferes with visual processing.' Jenni is well known for her work with children with learning difficulties, and she regularly takes referrals from special-needs schools and educational psychologists.

For optometrists with no direct experience of colorimetry or who don't feel comfortable with treating children, there is no harm in doing initial tests with coloured lenses, and if they feel that colorimetry might then be useful, they can refer patients on to a practice with a colorimeter. There are now about 100 of these in the UK and it can make such a difference. I find it very satisfying when you can help a child read mole fluently."