We have been opticians for three generations
in our family, and our activity is targeted on three areas, optometry,
contact lenses and optical instruments.
Correction by glasses. UNIFOCAL
glasses correct all types of near or long distance
vision defects. BIFOCALS correct near and distance vision defects
simultaneously.
TRIFOCALS
correct near, long distance and intermediary vision defects. VARIFCOALS
correct vision defects at all distances simultaneously and
progressively.
Glasses can be ORGANIC
or MINERAL,
white or tinted, phototropes, with or without surface treatment.
UV ABSORPTION WITH DIFFERENT KIND OF LENS MATERIAL
COLOUR AND OPHTHALMIC GLASSES
The scope and application of coloured lenses art huge and varied. With uses
ranging from pure aesthetics, fashion and sports to medical and safely
applications, and with the infinite variety of fixed tints, graduated tints and
the variable shades of photochromics, it can be difficult to know how
practitioners can best advise wearers about the vast choice available.
We will also discuss how opticians can quickly tint lenses th themselves at
the point of dispensing and the use of in-practice
aids for choosing and displaying coloured lenses. Years ago the choice of
coloured spectacle lenses was restricted
to a very small range of tinted-glass blanks. This range was extended, firstly,
when it became possible to apply colour to the surface of glass lenses by vacuum
coating. Subsequently, with the advent of CR39 lens production and economic dye
tinting, it became possible to produce an almost infinite variety of colours.
The wide variety of different hard coats and of high index lens material adds a
degree of complexity to the manufacture of coloured lenses, but in theory at
least, almost any colour shade, hue, and graduation are now achievable. While
cosmetic choice is a primary factor in choosing colour, there are also many
other reasons for opticians to recommend tinted lenses. These range from glare
reduction provided by conventional sunglasses, through contrast enhancing tints
for various sporting activities, to medical applications, such as relieving
photosensitivity and cataract protection.
Tints for driving are also available where special care has been given to
ensuring conformity with the European standards traffic signal recognition
criteria.
WHAT IS COLOUR?
Apart from 'visible' colour, there is also what might be called the
'invisible' parts of the spectrum of light, including ultra-violet and
infra-red. While 'visible' colour enhances the eye's functionality, UV can be
potentially harmful and the inclusion of a UV absorber or filter into both clear
and tinted spectacle lenses should be advised by dispensers. There is also a
special region, which has generated rich discussion recently - the near UV/blue
light part of the spectrum. This wavelength can have detrimental effects on
vision.
It is a section of the light spectrum responsible for hazy vision and low
contrast - potentially dangerous in many circumstances. So-called 'blue-
blocker' colour filters, which are designed to cut out this particular colour
wavelength, enhance contrast, and also create clearer outdoor distance vision by
reducing atmospheric haze. The haze comes about because of very small water
droplets naturally present in the atmosphere whose wavelength is equal to that
of blue light. Light at the red end of the spectrum has a longer wavelength and
hence is not affected.
The eye itself is a remarkable device not only does the eye have variable
aperture and variable focusing, but as it transmits messages to the brain it
processes complex images in ways that are still only vaguely understood; and it
does so apparently without any effort on out part. All the more remarkable is
how we recognize all the colours of the rainbow with only three types of
high-energy sensors (the red, green and blue cones in the retina) and only one
type of low-energy sensor (the rods). The electrical messages from each of these
sensors are sent to the cortex of the brain along interconnecting visual
pathways, making it difficult to say how much of the visual process happens in
the eye, and how much occurs in the brain.
The limited number of colour- recognizing cones does mean that it is possible
for the eye to be 'fooled' into thinking that it is receiving one colour when in
reality, the object is made up of different colours. For instance, is an object
really green, or is it a combination of blue and yellow - only a scientific
measurement of the spectrum can actually answer this question. However, a purely
scientific analysis of colour can be misleading because the eye is not equally
sensitive to different colours; also its colour sensitivity varies between
daylight and evening light. These are known as 'photopic' and 'scotopic' eye
sensitivities, the first of which is illustrated.
Lighting also plays a significant role in the recognition of colour, and
tinted lenses can apparently change colour when viewed under different lighting
conditions. While the energy of sunlight is spread fairly evenly through the
spectrum, incandescent lights radiate considerably mole red than blue light, and
fluorescent lights emit light at only a few specific wavelengths.
(In fact it is only by use of a special coating on the inside of fluorescent
lighting tubes that a moderately white colour is transmitted.) How does a
coloured lens create or alter colour, when it is essentially acting as a filter
which blocks light? The answer lies in the fact that to 'create' one colour in
the spectrum, it 'destroys' the complementary colour. This is best explained
with an example. When a lens contains special tint molecules to absorb blue
light, this will allow the other colours of the spectrum (mainly yellow) to pass
through and create a lens with a yellow appearance.
Where does the blue light go? Since energy cannot be destroyed, it ends up
being converted into heat energy by the tint molecules. As an alternative to
absorption, it is also possible to reflect light, a method adopted in mirror
coatings. Again the complementary colour theory applies, so that a 'blue' mirror
allows yellow light to be transmitted.
The increased use of AR coating does restrict the ability of opticians to
tint lenses at the point of dispensing (AR is non water permeable, so dyes will
not be absorbed). The AR needs to be applied after the tinting treatment.
However, is it logical to have an AR coating (which increases transmission) in
combination with a tint (which reduces transmission)? The answer is certainly
yes: the combination of AR with a tint can be very beneficial. An AR coating on
the concave side of dark tinted lenses is in many cases essential to prevent
concave surface reflections affecting vision. AR and colour should be seen as
complementary.
A great range of special coloured filters is now available and these offer
many opportunities for optical professionals to both enhance their
professionalism, and offer benefits to spectacle wearers. While the use of
tinted lens displays can help, a knowledgeable explanation of the visual
advantages of specially coloured lenses by the dispenser will likely prove the
convincing for the costumer.
20/20 Europe 10/2000
CONTACT LENSES
The contact lenses create an artificial cornea , in order to correct
nearly every optical faults of the eye. go to the page
CONTACT LENS
Orthokeratology uses Contact Lenses to remould the Cornea, to reduce or correct
Myopic (short-sighted) and Astigmatic (irregular surface) errors of the eye.The
Cornea is highly elastic, and always returns to its original shape. For this
reason the lenses are worn nightly or on alternate nights after the ideal
Corneal shape has been achieved and removed in the morning giving perfect vision
without the need for spectacles or contact lenses.
CORNEAL SURGERY
The cornea surgery is made, by radial cuts in the cornea (FEDOROV)
or by scraping with EXCIMER laser. With the (FEDOROV) technique, one
counts on the capacity of the cornea tissues to heal up, in order
to have the optical modification of the cornea. With the EXCIMER technique,
one counts on the shape made with the laser to have the optical modifications
of the cornea. These surgeries are made by a specialized
ophthalmologist.
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