Download ChromaGenColour - Aaron Optometrists

Introduction
The trichromatic theory states colour vision results from the stimulation of three cone
photopigments with different spectral sensitivities, in much the same way a colour TV
screen produces full colour from the mixing of red, green and blue. Experiments demonstrate
normal observers need to mix three wavelengths, in different proportions, in order to
match a single test colour.
The trichromatic mechanism occurs at the actual cone cells within the retina. There is also
further neural refinement of colour perception at a higher brain level. This more complex
‘opponent’ theory is beyond the scope of this leaflet.
Colour Vision Anomalies
There are essentially three types of colour deficiency : monochromatism, dichromatism and
anomalous trichromatism.
In monochromatism the patient has only one functioning photopigment and sees in shades
of one colour and white. This colour deficiency is extremely rare.
Dichromatism is where one photopigment is missing. The patient is left with only two
functioning cone photopigments, the red (long wavelength), green (middle wavelength) or
short wavelength (blue) is missing.
Anomalous trichromatism is a reduction in function of one or more of the photopigments,
such that, although all three are present, the patient still exhibits defective colour vision.
Anomalous trichromats are subdivided into protanomalous (red : long wavelength defective),
deuteranomalous (green : middle wavelength defective) or tritanomalous (blue : long wave
length defective).
There is a wide variation in severity of the defect amongst anomalous trichromats,
depending on how dysfunctional each photpigment is.
The protanomalous defect is considered the more dangerous type of colour vision defect
due to the inability to distinguish red.
Colour Enhancement
As early as 1854 colour overlays were found to enhance the colour perception of people
with colour vision defects.
The ChromaGen clinical trials in the 1990s identified specific filters of varying hues and
densities, were found to enhance colour vision in 80% of people trialled. The filter is
patient specific and can only be ascertained after a full clinical trial.
Patients must have realistic expectations of what ChromaGen can achieve. ChromaGen
lenses certainly do NOT cure colour blindness and do not give ‘normal’ colour vision. The lens
is simply intended to enhance colour vision.
REALISTICALLY CHROMAGEN LENSES CAN :*improve general colour perception
*make colours brighter and clearer
*allow shades of colour, previously unseen to be observed and discriminated
*improve colour naming (after adjustment to the new stimulii)
*improve safety by allowing florescent lights to be distinguished more easily
*improve performance on some colour vision tests
PATIENTS MUST NOT BE ALLOWED TO BELIEVE THAT THE LENSES CAN :*Cure colour blindness
*enable immediate ability to name all colours correctly
*enable the patient to pass all colour vision tests
Some occupations demand accurate colour vision and may not accept colour
enhancement with ChromaGen lenses as satisfactory. ChromaGen lenses have been
used successfully for electricians, electrical engineers, graphic artists, police officers,
sign writers, textile workers, photographers and many others. If ChromaGen is to be
considered for vocational reasons the requirements from the employers should be
ascertained before proceeding with a trial. A report can be prepared for the
employer on request.
ChromaGen Trial
A full eye examination is required to assess general ocular health, followed by colour
vision assessments. Any refractive error found can be incorporated into the final
contact lens.
Eye dominance needs to be ascertained as, usually, the filters are placed before
the non dominant eye.
Normal preliminary tests for suitability to wear contact lenses (tear quality, tear scope,
phenol red thread, meibomian gland function, corneal topograpghy) are also
essential.
During the filter assessment the
practitioner holds trial lenses in front of
the patient’s non dominant eye while
they view the computerised colour fan
binocularly. Successful filters may
produce increased brightness of the
colour fringes; increased numbers of
colour fringes seen, fluorescence of
some colours or a ‘3D’ effect. To
compare normal vision to enhanced
vision the patient need only to shut
the non dominant eye or remove the
filter.
Once the appropriate filter is identified the corresponding contact lens is inserted.
Occasionally we may then try an extra filter over the dominant eye as well, but
normally this is not necessary.
Since vision quality is a very subjective phenomenon, the patient must be allowed to
leave the practice for at least an hour to experience the new colour perception. Parks,
shopping centres or garden centres are ideal places for the patient to visit during the
trial. It is the patient’s response to this trial that indicates success or failure. Only the
patient can grade the subjective improvement.
Costs
The initial trial, including a full eye examination and assessment for contact lens
suitability is £50.00. This can take up to three hours.
If successful the lenses are £200.00 each. Generally only one lens is required.
As for all contact lens wearers the fees cover all aftercares, both scheduled and
emergency (see our contact lens leaflets).