GB2374428A

GB2374428A - Testing for colour preference and light sensitivity using tinted lenses

Info

Publication number: GB2374428A
Application number: GB0109172A
Authority: GB
Inventors: Geraint William Griffiths
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-04-10
Filing date: 2001-04-10
Publication date: 2002-10-16
Anticipated expiration: 2021-04-10
Also published as: GB0109172D0; GB2374428B

Abstract

The apparatus may consist of 6 pairs of coloured lenses (pink, orange, yellow, green, blue, violet) and one pair of grey neutral density filters, glazed into lorgnettes. Each set of lenses is held close to the subject's eyes in turn, who is asked to say if he likes the feel of the lens or hates it or something in between. When a selection of lenses have been chosen as good and bad, the choice may be further refined by forcing a choice between successive pairs (is it better with number 1 or number 2) until a single colour is left of the favourite ones and a single colour of the worst ones. It has been shown that colour preference is specific to individuals and groups and needs to be taken into account together with the physical properties of the tint or filter when prescribing. Prescribing of tint is important in many areas. It can help to prevent serious eye disease, visual discomfort and relieve the symptoms of migraine and dyslexia.

Description

EYE BRIGHT - A TEST FOR MEASURING AND PRESCRIBING FOR LIGHT SENSITIVITY DESCRIPTION The testing set consists of 6 pairs of non prescription coloured lenses (filters) and a control neutral density filter, mounted in a lorgnettes. The lorgnettes have a centration distance of 75mm and round eye shape, diameter 55mm. The regular bridge size is 15mm and the distance between lenses 20mm These measurement again do not have to be precise, but sufficient to be able to hold the lorgnette comfortably close to the subjects face so that most of the light reaching the eyes comes through the lenses. (see Fig 1 Dimensions of the Lorgnette) The light transmission factor is about 65% for each set of lenses.

The precise wavelength of each filter is not important but should be about the middle of the range generally accepted to be the colour indicated. (See Fig 2 colours used and wavelength guide). The lenses are not coated separately to absorb Ultra-Violet radiation (UV) specifically.

BACKGROUND Choice of colour, or colour preference is deeply rooted in psychology and evolution. Red is often associated with danger (fire, poisonous berries) and so is the combination of yellow and black seen on wasps and venomous snakes.

It may not be a coincidence that the natural colours of fields and forests and the blue of the sky and the sea are calming.

Colour preference can also be affected by pathological conditions like cataract, The French impressionist Monet was deeply disturbed by the effect cataract had on his colour perception. Macular degeneration and systemic disorders which affect cone function are also likely to have an effect. Complicated neurological disorders like dyslexia and associated conditions, migraine and epilepsy have been shown to be affected by looking through a coloured material.

THE HAZARDS OF COLOUR The colour of light is an indication of wavelength and in some cases an associated danger.

Blue light and Ultra violet (UV) are implicated in cataract formation and macular degeneration. These shorter wavelengths are not dealt with easily by the eye, UV causes the lens to fluoresce and blue light is focused in front of the retina, contributing to a veiling luminance and reduced contrast sensitivity.

Infra red (IR) can cause cataracts in blast furnace workers. It may be the heat in IR which increases the prevalence of a predisposition to cataract in people with brown eyes over the age of 45, the iris acting as a heat sink on top of the lens.

When light is intense in the orange/yellow part of the spectrum, to which the eye is most sensitive, it can lead to disability glare. Although filters will not necessarily increase the contrast thresholds, they will save the retina from being unnecessarily bleached and the implications in terms of dark adaptation and long term dysfunction of the macular.

The ability to distinguish between wavelengths in the electro magnetic spectrum is useful in industry, where colour coding is used to convey information quickly. This can be a disadvantage in some professions for about 8% of the male population who are colour blind. For that 8% it has been proposed that a red tinted lens improves hue discrimination by increasing the relative brightness of red.

Understanding the physical effects of tinted lenses is important when it comes to the final dispensing, but the usefulness of tints is not fully understood.

In the hospital eye service tints may be seen as clinically necessary for well established reasons like albinism, aniridia and trabeculectomy damage, or symptomatic age related macular degeneration, cataracts and aphakia.

On the NHS examination claim forms tints have to be justified in a way which other parts of the prescription are not. In neither situation is there clear guidance about the frequency of prescribing and which colour is best and why. When there is a lack of professional consensus funding authorities will tend to be the final arbiter.

Given the and the potential of tinting to relieve symptoms and prevent disease, there needs to be a convenient way of measuring colour preference in general practice.

THE COLORIMETER Anecdotally some practitioners believe that tints should never be prescribed and have little value in the treatment of dyslexia and migraine and this may have contributed to the scepticism of early work with coloured overlays and reading disability The colorimeter has established for the first time that individuals can have distinct and precise colour preferences.

A SCREENING TEST FOR COLOUR PREFERENCE The colorimeter provides an exhaustive test for colour preference but is necessarily time consuming and does not fit easily into a routine eye test It is also suggested that the colour of the overlay does not produce the same effect when dispensed in spectacles, but it has been suggested in a preliminary study that contact lenses, can improve reading in dyslexia.

Subjectively the effect of tints seems stronger when worn compared with being held at a distance over the printed page, perhaps because the peripheral field IS involved.

Although the colorimeter confirms that tinted lenses have an effect it may be necessary to measure colour preference and light sensitivity in a different way when prescribing specifically for spectacles. It may not be necessary, to define colour preference so precisely when considering the broader use of therapeutic tints.

HYPOTHESIS If a sample of say 6 colours evenly spaced across the spectrum were chosen, it might be possible to establish that colour choice from this limited range could still be a basis for prescribing.

To test this hypothesis two groups of subjects were chosen from elite sport SUBJECTS 1. All England Netball Association Panel Umpires 'Screened at Nottingham University 6.9. 98 . N=33 'Average Age 44. 3

2 British National Smallbore Rifle Association Junior Squad 'Screened at Chesterfield 25.5. 97 and Aldersley 21.4. 00 . N = 51 * Average Age 20.5 The umpires were tested in an indoor sports hall with no outside windows, the shooters mainly in a large room in a sports centre which was open to the daylight.

A smaller group of the shooters were also tested outside.

METHOD Each lorgnette is presented at random. Subjects are asked to say if they like the feel of the lens or hate it, or something in between. They are then asked to look as some distant object in the prevailing ambient light (ideally relevant to their sport, like a target in shooting). The instructions are as open as possible to encourage the subject not to base their choice on pre-conceptions.

In the optometric consulting room conditions can be standardised. A high contrast, internally illuminated test chart, is a suitable target with the room illumination turned up as high as possible. Fluorescent light with its spiky emissions and UV content is a good simulation of indoor which can cause problems.

The favoured tints are placed in one group and the least favoured in another.

Preference is judged on three levels : 'Strong, 'Medium 'Weak.

The choice can then be narrowed by forcing a choice between pairs of filters. The subject is asked to say if it is better with the first filter or the second. The first choice is retained and compared with the next one in the favoured group. (When a preference for a group of tints has been expressed it is very rare for the subject not to be able to decide which of the remaining favoured tints is the best).

If there is no colour preference there are two further divisions : . All colours chosen, this indicates no preference and good tolerance of colour distortion.

'None of the tints chosen, indicates Intolerance of colour distortion.

RECORDING RESULTS The reference number for each lorgnette is recorded on the data sheet (See Fig 3 Data sheet) CHARACTERISTICS OF The EYE BRIGHT Test 1. The Eye Bright Test (EBT) is specific to individuals and groups (see fig 4 test results in shooters and Umpires, and Fig 5 Analysis of the results using the Chi Squared Test) 2. Two groups of tints are mutually exclusive, green, blue, grey and orange, yellow.

It is extremely rare for the best and worst tint to be chosen from the same group (see Fig 6 Mutually exclusive tint groups) 3. Eye Bright results are not strongly affected by lighting conditions (see Fig 7 favourite colours indoors and outdoors 4. A choice of blue as the best colour and yellow as the worst is diagnostic of light sensitivity in a young healthy eye.

5. The prescription of tints follows from the EBT results (which are a summation of psychological, neurological and physiological characteristics) and the physical properties of the filter. These are the characteristics of various colours and groups.

Blue/Green and Yellow/orange These groups are almost mutually exclusive. Of all negative responses the greatest is to yellow and orange and this was very often in blue eyed subjects.

Yellow A yellow filter increases the contrast between that colour and the surrounding colours, this concentrates light in the area of the spectrum to which the eye is most sensitive. If an individual is already light sensitive then the experience is heightened looking through a yellow or orange filter Someone who is not light sensitive would appreciate the contrast-enhancing elimination of the blue/ultra-violet (UV) end of the spectrum.

Blue Vs Yellow In particularly light sensitive individuals the light scattering effect of blue light is outweighed by the relief they get from the elimination of peak sensitivity wave lengths in the yellow and orange.

If however there are media changes which increase the scattering effect of blue and UV then preference may change. In light sensitive people this would be towards a longer wavelength like green, which absorbs blue and UV but still subdues the effect of yellow and orange. Someone who is less light sensitive but still has some clouding of the media might choose orange (the effect of a brown tint) which will reduce general light levels and eliminate blue and UV.

It could be concluded from this that a best choice of blue and a worst choice of yellow is diagnostic of clinically significant light sensitivity in a (young) healthy eye. Looking at the frequency of choice of blue and yellow shows that the characteristics of the two groups are very different. (see Fig 8 choice of yellow and blue) The yellow contrast enhancing filter is likely to be favoured in a visually demanding sport like shooting, but it also implies that shooters do not tend to be light sensitive.

In the older group, the Umpires, the tendency is completely reversed. Perhaps this is an ageing effect due to benign media opacities or perhaps umpires self select because of the mainly indoor nature of netball and a natural sensitivity to light.

Blue/Grey If there is a strong preference for blue its prescription for outdoor use should be avoided because: It is likely to transmit the more dangerous high energy part of the spectrum (short wavelength blue and UV). The eye's lack of sensitivity to this part of the spectrum adds to the danger.

The darkening effect of blue would allow the pupils to dilate and increase exposure.

In young light sensitive children a suitable alternative would be neutral grey or green, with a UV block, if there is a high transmission factor, say LT 60 and above.

Pink And Violet These colours are at opposite ends of the spectrum and were only grouped together because as a pair they were the least popular, that in itself make their choice when it occurs, interesting.

Violet was the least chosen tint of all and it may be that the glare due to short wavelength transmission and the darkening effect, was too great even for light sensitive subjects.

Pink When the choice of tint was compared for light (blue/green irides) and dark (brown irides), the most popular tint for dark eyes was pink, which was not chosen by any of the umpires with light coloured eyes (see Fig 9 Tint preference, most and least preferred, for light and dark eyes).

This could suggest that vision in brown eyes, which are more prone to early lens changes, degrades as the pupil expands. The pupil in a blue eye might expand less because the eye is relatively more sensitive even in low light levels. Pink has the bright feel favoured by non light sensitive subjects and is still a good UV and blue light absorber.

Pink I red has been shown to be useful in hue discrimination in colour blindness and early results in the Author's unpublished research, points to migraine sufferers making this unusual choice. Pink might be the colour of choice when there are neurological problems as opposed to physical and physiological.

In colour deficiency a red tint has helped hue discrimination This effect might be enhanced by relating the tint to the anomaly, a red tint for protanopes and a green for deuteranopes. It is possible that the choice will not be as simple as this (or the reverse, red for deuteranopes) or that the greatest effect is achieved by another colour or different colours in each eye.

Green The choice of green is interesting because it has good UV and blue light absorption, but has a peak of transmission quite close to yellow. It should also have good Infra Red (IR) heat absorbing properties. This combination of factors would maximise visual information whilst providing necessary protection from peak

brightness in the yellow. The pupil would remain relatively constricted and heat effect minimised.

The transmission curve for a typical green tint illustrates the peak in the most visible part of the spectrum and absorption of the shorter blue and UV wavelengths (see Fig 10 Transmission spectrum for a green tint) FUTURE DEVELOPMENTS Several points follow form the results and discussion which could be the subject of future research leading to more tests:

A test for predisposition to macular degeneration in pre a post cataract patients.

A test for predisposition to cataract.

A test for a predisposition to reduced accommodation.

A test for colour deficiency, or enhancement in known colour deficiency.

A test for the effect of colour rendering of light sources on colour preference and light sensitivity contrast sensitivity.

A test for the effect of an Ultraviolet block on colour preference, light sensitivity and contrast sensitivity.

A test for the effect of an anti-reflection coating on colour preference light sensitivity and contrast sensitivity.

Claims

CLAIMS 1. A test for measuring colour preference and light sensitivity in which tinted lenses mounted in a lorgnette frame are shown successively to a subject, who is asked to choose which is the favourite colour and which is the worst.
2. A test as claimed in claim 1 in which there are six different coloured lenses and one pair of neutral density filters
3. A test as claimed in claim 1 in which the average light transmission of the lenses is in the region of 65%.
4. A test as claimed in claim 1 in which the colours of the lenses are nominally ; pink, orange, yellow, green, blue, violet and grey
5. A test as claimed in claim 1 in which the precise wavelength of each filter is not important but should be about the middle of the range generally accepted to be the colour indicated.
6. A test as claimed in claim 1 in which there is no additional Ultraviolet block.
7. A test as claimed in claim 1 where the choice of colour or neutral grey can be used to precribe tinted lenses from the available manufacturing range for all variations of physiology and pathology which are associatied with light sensitivity.

7. A test as claimed in claim 1 in which there is no additional anti-reflection coating.

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1 A test for measuring and prescribing for light sensitivity in which 6 pairs of coloured lenses and one grey pair of lenses, average light transmission 65%, are mounted in lorgnette frames and shown successively to a subject, who is asked to choose which is the favounte colour and which is the worst 2 A test as claimed in claim 1 in which the coloured lenses, pink, orange, yellow, green, blue, violet have a wavelength at the middle of the range generally accepted to be the colour indicated.

3 A test as claimed in claim 1 which takes 3 minutes to carry out.

4. A test as claimed in claim 1 which measures sensitivity to natural daylight and artificial light sources.

5. A test as claimed in claim 1 where a favourite colour of blue and a worst colour of yellow, is diagnostic of light sensitivity.

6 A test as claimed in claim 1 where a choice of pink orange or yellow indicates low light sensitivity and a choice of green blue violet or grey, indicates high light sensitivity.