Choose Background Color

Click color to lock/unlock


Irlen Coloured Filters for Reading: a Six-Year Follow-up

Paul R. Whiting, G.L.W.Robinson and C.F. Parrott

In 1985, media publicity based on reports from Hong Kong and California suggested that the use of coloured filters might assist persons who had difficulty with reading and other near-point tasks associated with the interpretation of print (spelling, handwriting). It was suggested that sensitivity to high contrast (black-on-white) was the reason that some visually sensitive individuals found reading and similar tasks difficult. These individuals perceived print as unstable, and were not as easily able to keep it in focus, or to register, at one fixation, a clear image of as much print as normal readers.

Irlen (1983) has called these difficulties "scotopic sensitivity syndrome" because of the hypothesized role of the rods of the retina in producing the anomalous visual effects. Although there is some evidence that dyslexics have a different distribution of rods and cones on the retina, and that they make more use of parafoveal information when reading than do normal readers (Geiger & Lettvin,1987; Grosser & Spafford, 1989; Spafford & Grosser, 1991; Solman, Dain & Keech, 1991), current theories favour an explanation which looks at the operation of the parvo- and magnocellular visual pathways in the brain (Livingstone, Rosen, Drislane, Galaburda, 1991). Because of this, the group of symptoms is now often referred to as Irlen syndrome.

In descriptive papers, Whiting (1985, 1993) has specified five areas of difficulty experienced by children and adults who claimed to have these problems. The first area was photophobia, usually experienced as finding white paper too bright, or competing with the print for the readerís attention. Many readers alleging this difficulty also had problems with bright sunlight, fluorescent lights, and headlights and street lights at night.

The second area of difficulty was visual resolution, usually experienced as perceiving the print to distort in some way. It might seem to vibrate as the reader stared at it, to move in some other way, or to fade, become elongated, or to thicken until it looked like a solid black block. Thirdly, such readers reported that they perceived only small portions of the print at one fixation. This apparently restricted focus varied from perceiving only one letter at a time, to seeing slightly more than a short word. Normal readers see more than this, and some claim to be able to see half a page at one fixation, at least well enough to be able to register those visual cues necessary to interpret the meaning of the print in that area.

The fourth area of difficulty described was sustaining focus where the print seemed to blur after a short period of time. Experiences of this effect ranged from immediate blurring of the print (though eyesight was good or corrected) to blurring after a few minutes of reading. The fifth area was eyestrain. Again, this was experienced when reading, even though eyesight had been tested as normal or had been corrected using optical lenses.

In addition, some subjects reported difficulties with depth perception, experienced as difficulty in accurately judging distance when driving a car, parking a car, catching a ball on the full, walking down stairs, escalators, or just in walking through doorways, with another person, etc.

Irlen (1983, 1991) suggested that, where a number of such difficulties occurred in one person, they could be alleviated in a majority of cases by the use of precisely tinted filters, applied to the normal or corrected vision of the subject. Her clinic at the University of California had trialled this method on adult subjects with some apparent success. Clinical trials in Australia also seemed promising, according to surveys carried out after subjects had used filters for more than twelve months (Whiting, 1988; Whiting & Robinson, 1988).

In the past eight years, a number of research papers on the subject have appeared. A useful summary of the state of research specifically related to Irlen filters up to 1990 is Lea and Hailey (1991). Some research has produced negative or inconclusive findings (Stanley, 1987; Winter, 1987; Saint John & White, 1988, Cotton & Evans, 1990), while other research has produced positive results, sometimes remarkably so (Adler & Atwood, 1987; Chan & Robinson, 1989; Fricker, 1989; OíConnor, Sofo, Kendall & Olsen, 1990; Robinson & Conway, 1990; Burgess, 1991). However, most of the studies producing negative findings did not use Irlen filters; the studies producing positive findings did. When coloured overlays applied to the page were used rather than lenses, both negative and positive findings have resulted. General psychological research on the use of filters to reduce visual perceptual difficulties has generally been positive, however (Solman, Dain & Keech, 1991; Williams, Lecluyse & Rock-Faucheux, 1992). Each study, positive and negative, has been criticised for lack of rigour (see, e.g., Robinson 1990).

It is certain, however, that to carry out empirical research that satisfies everyone on such a subject is very difficult. For one thing, it is virtually impossible to control for the subjectsí commitment to the outcome being positive. The only way in which appropriate colours and densities can be determined is by reporting of symptoms, followed by reporting of changes as various combinations are applied. When the filters are used, the changes are present. When the filters are removed, the changes disappear, and all the old difficulties are present once again. It is thus not possible to determine and apply the prosthesis without the subject being involved in that determination. This makes a placebo-controlled study very difficult (though one such study is currently under way which attempts to keep the colour of the filter visually similar to the chosen combination, while altering its light-transmission characteristics).

Another problem is the fact that Irlen filters or their formulas are patented and thus not readily available for trial by independent observers also puts a difficulty in the way of researchers, though independent psychological studies of the effects of colour filtering, some of which are referred to above, have helped to overcome this problem to some extent. The numbers of studies also tend to be small because the procedure for correct specification of Irlen filters is time consuming and requires special training (the diagnostic and specification session takes about 2 hours for each individual: training takes one week or more). It is thus difficult for researchers to build up a large body of controlled data which can be followed up in an empirical study.

One of the major objections to the idea of using colour filtering to improve reading performance has been that there was no theoretical rationale for believing that such a prosthesis could have the effects described by those who alleged its effectiveness. Recent research, however, has suggested strongly that colour filtering modifies the way in which visual signals are transmitted from the retina to the cortex, (Wiliams, Lecluyse & Rock-Faucheux, 1992). In particular, physiological research on the visual pathways in the brains of dyslexic and normal readers has shown that there are apparently consistent differences in the operation and cellular structure of the visual pathways (Livingstone, Rosen, Drislane & Galaburda, 1991; Lehmkuhle, Garzia, Turner, Hash & Baro, 1993). These differences appear to explain why many dyslexics have such difficulty with the visual processing of print, and why, if the processing is modified using appropriate filtering of colour and density, the visual image appears to be clarified, and reading made easier as a consequence.

Survey research

There have been a number of attempts to follow up clients from the clinics offering treatment for reading problems using Irlen filters. As mentioned above, Whiting (1988) and Whiting and Robinson (1988) attempted to follow up some 465 subjects who had been provided with Irlen filters more than twelve months previously. They asked subjects to respond to a questionnaire asking whether they had previously had a problem with a number of factors related to reading, and whether they had experienced any improvements since using Irlen filters. The factors were things such as fluency, overall difficulty (reading is a task that requires effort), comprehension, concentration, eyestrain, visual confusions, tendency to skip lines, etc. Questions were also asked about handwriting and spelling, as well as overall self-confidence, and tiredness. Improvements were rated as "none". "some" and "large". Subjects were considered to have experienced a large measure of help overall from the filters only if they rated three or more factors as having shown a large improvement. If fewer than three factors were rated as having shown a large improvement, the overall result was rated as "some" improvement. There was also a percentage of people who experienced no improvements at all.

Of the 213 responses examined, 93% had experienced improvement since wearing the filters, and 57% of the respondents experienced a large improvement. The main areas of improvement were fluency, eyestrain, concentration and comprehension. The area showing least improvement was handwriting (28% indicated no improvement, while 14% had not had a problem in this area). The fact that this is largely a motor skill would lead one to expect that improvements in visual perception might not have a great effect on handwriting.

Stokes & Stokes (1990) surveyed 160 subjects in Louisiana, Alabama and Mississippi who had worn Irlen filters for at least three months (mean length of time using filters was 6.69 months). Sixty-nine responded to the questionnaire. Of these respondents, 7% stated that the filters did not help their reading. Ninety-three percent stated that the filters definitely helped their reading. Improvements were also reported in incidence of headaches while reading (49% stated that they no longer got headaches while reading), and sleepiness (67% stated that they no longer became sleepy while reading).

Burgess (1991) replicated and extended the Whiting and Robinson study, using 306 subjects randomly selected from a clinic population of 1500 in Canberra. She obtained 175 responses (57%), and concluded that her results were very similar to those of Robinson and Whiting. She also asked questions about improvements in mathematics, depth perception and coordination, and motion sickness. In these areas, 48% reported improvements in mathematics, 41% in depth perception, and 24% in motion sickness. Because she used a five-point scale, it was not possible to compare overall improvements directly, but 83% stated that they had experienced "great benefits" from wearing Irlen filters. The areas of greatest improvement in her study were overall difficulty of reading (91%), eyestrain (86%) and fluency (85%). The areas of greatest improvement seemed to be overall difficulty of reading ("reading is hard"), eyestrain, fluency and tiredness when reading. Tendency to skip lines and visual confusions were also significantly improved, according to her statistics. A summary of these results is in Table 2, for comparison with other studies.

In 1993, Westergard (1993) surveyed 149 respondents who had obtained Irlen filters and were living in Washington, Idaho, Montana and Oregon. The respondents had used Irlen filters for an average of 36 months. Of these subjects, 61% indicated that the filters had been very helpful to them, while 86% indicated that they had been somewhat or very helpful. Seven % had found no help at all from the filters. A further 7% had not used the filters at all for a variety of reasons. (One man commented, "I just haven't given them a chance. I don't like or need glasses to read, so that's that!") In this study, the area of greatest improvement was eyestrain, followed by difficulty of reading, then concentration, fluency, skipping lines, and visual confusions.

Six-year follow up

The present study followed up 267 clients who had been surveyed in the earlier study (Whiting & Robinson, 1988), and who had had Irlen filters for a minimum of six years, to see the extent to which they now rated the filters a help. Although it was felt that a period longer than a year was sufficient to minimise possible placebo effects, an even longer period would give more confidence in the results.

Subjects were surveyed by mail. Initially, 31% replied. As in the survey reported in 1988 (Whiting & Robinson, 1988), others were followed up by telephone, so that 114 (43%) of those surveyed eventually responded. The instrument used was identical to that used in the 1987 survey.

Results

The results are summarised in Table 1

Table 1. Numbers and Percentages of subjects reporting improvements in various categories of difficulty associated with reading after having Irlen filters for six years or more.

 

before filters

improvement since filters

 

Problem

None

Some

Large

   

 

No

%

No

%

No

%

No

%

   

It is very hard to read

93

83

11

10

44

42

51

48

   

Reading is very slow or word-by word

103

92

12

11

44

45

47

43

   

Problems understanding what is read

102

93

17

16.5

52

50.5

34

33

   

Cannot read for very long without losing concentration

104

95

14

12

46

39

57

49

   

Eyes become sore, strained, tired, etc.

93

82

23

22

35

34

45

44

   

Avoid reading - never read for pleasure -

96

86

25

24

50

48

30

28

   

Lines are skipped or reread

100

91

11

10.5

41

39.5

52

50

   

Often mistakes words and letters having similar shapes

99

88

8

8

33

33

60

59

   

Performing at school below ability level

52

69

15

24

19

30

29

46

   

Handwriting

80

71

39

39

36

36

25

25

   

Spelling

100

90

31

29

55

51

21

20

   

Low opinion of self - lacks confidence

79

71

22

23

39

42

33

35

   

Gives up when things become difficult -often gets discouraged

85

75

28

30

28

30

37

40

   

Not doing as well at school or in career as would like

87

78

19

20

37

38

40

42

   

Tires very quickly

80

73

30

32

39

41

25

27

   

 

(For a few of the questions above, respondents registered improvements in factors they had not perceived as problems before they had the lenses. In these cases, the total ns in the "improvement" column will exceed the number in the "before lenses " column.)

 

The problems most often reported are concentration, comprehension, fluency, skipping lines, spelling, confusion of words or letters, as well as overall difficulty and eyestrain. These are the typical dyslexic symptoms (Aaron, 1990). The factor least often reported was "performance at school below ability level", partly because many respondents did not answer the question, but perhaps also reflecting the common confusion of dyslexic or specific reading problems with assessments of general ability.

As with the earlier studies (see Table 2), the most obvious areas of reported improvements are overall difficulty of reading ("reading is hard"), visual confusions, tendency to skip lines, fluency, concentration, and comprehension. These are all areas where improvements would be expected if part of the subject's difficulties was with visual perception. Most "large" improvements were in similar areas: visual confusions, skipping lines unintentionally, concentration, overall difficulty of reading, and fluency. The order is different, but the factors are the same, with the exception of comprehension. Comprehension, being a factor involving complex processes, would be expected to take longer to show large improvement, especially in cases where decoding skills were particularly weak (Blaski et al, 1990; Robinson & Conway, 1990). Given the subjective nature of the ratings of "some" and "large", however, it seems most useful to limit observations to the ratings that combine the two categories. (See Table 2) below.

The rate of overall usefulness of the filters, as described by respondents, was calculated using the same method as used in the earlier study. In that study, Whiting & Robinson (1988) used a criterion of three or more "Large" responses to determine that the filters had been of considerable help to a subject. Fewer than three "large" responses, with any number of "some" responses indicated that the filters had been of some help to the subject, while a consistent response of "none" indicated that the filters had been of no help at all. As in the earlier study, there were a number of reasons given for "no help", including that the subject had never worn the filters because of peer pressure. In this study, 104 respondents (94%) reported that the filters had been of "some" or "large" help (as defined above), while 7 (6%) indicated no help at all. Sixty-six (58%) indicated that they had received a "Large" degree of help, while 41 (36%) indicated they had received "Some" help. While these figures are higher than Burgessís (1991) results, they are almost identical with Robinson & Whitingís (1988) results using the same sample. Burgess speculated that her figures might be different because her subjects had had the filters for only six months, while Whiting & Robinsonís had had them for at least 12 months. The six-year study however, tends to support the earlier figures obtained by Whiting and Robinson (1988).

The telephone follow-up of non-responders suggested that they were much like those who responded to the mail survey, except that for various reasons they did not return the forms. Of those surveyed by telephone, 56% indicated a "large" degree of help from the filters, 35% indicated "some" help, and 9% indicated no help at all. The figures for the mail sample were 58%, 36% and 5% respectively. Thus there may have been slightly more non-respondents who had experienced no help, but the difference was not great. It seems reasonable to conclude that better than 90% experienced definite help from the filters.

Table 2 combines the categories "some" and "large" and presents a comparison of results from the two earlier studies discussed above (Whiting & Robinson, 1988; Burgess, 1991). Though there are obvious similarities in results, there are changes which are worth noting. For simplicity of comparison, only percentages have been given.

 

Table 2: Survey Research on Irlen Filters: Comparative Summary of Results from 3 studies.

Factor

Percent of subjects reporting improvements

 

A(1988)

B(1991)

C(1993)

A-C

     

Overall Improvement

93

83*

94

(+1)

     

Reading:

 

 

 

 

     

difficulty

91

91

90

(-1)

     

fluency

91

85

88

(-3)

     

comprehension

84

73

84

(=)

     

concentration

85

71

88

(+3)

     

Spelling

69

63

71

(+2)

     

Handwriting

58

54

61

(+3)

     

Mathematics

 

 

48

 

     

Visual anomalies:

 

 

 

 

     

skip lines

82

78

90

(+8)

     

confusion (inc. reversals)

81

76

92

(+11)

     

eyestrain

82

86

78

(-4)

     

tiredness (while reading)

56

81

68

(+12)

     

glare

 

77

 

 

     

Self confidence

 

68

54

77

     

Perseverance

 

 

51

70

     

Performance (school or career)

 

 

62

80 (children:

76

     

Depth perception, coordination

 

41

 

 

     

Motion sickness

 

24

 

 

     

*To obtain this figure, Burgess (1991) asked subjects to respond to the statement:"I/my child have experienced great benefits from wearing Irlen tinted lenses". The statement would naturally result in a lower figure because of the word "great" which excludes "some", included in the other figures.

 

The differences between the 1988 figures and the 1994 figures are negligible, with the exception of confusions of letters and words (+11%), tiredness while reading (+12%), and self-confidence (+9%). These increased responses could be attributed to an improvement in word attack skills, and a reduction in stress associated with reading as a result of reduced visual perceptual problems, and an increased belief that success in reading was possible. Reduced stress and improved confidence are not, however, necessarily to be thought of as a placebo effect; they may be an effect resulting from a real difference in visual perception: a belief based on the fact that text now appears clear, whereas before it appeared unclear or distorted in some way.

For the sake of comparison, Table 3 presents a summary of "large" improvements from the three studies cited in Table 2.

 

Table 3: Survey Research on Irlen Filters: Subjects reporting large improvements in three studies.

 

Factor

Percent of subjects reporting large improvements

 

A(1988)

B(1991)

C(1993)

C-A

     

Overall Improvement

57

83*

58

+1

     

Reading:

 

 

 

 

     

difficulty

38

57

48

+10

     

fluency

45

52

43

-2

     

comprehension

40

35

33

-7

     

concentration

42

53

49

+7

     

Spelling

35

23

20

-15

     

Handwriting

29

25

25

-4

     

Mathematics

 

24

 

 

     

Visual anomalies:

 

 

 

 

     

skip lines

34

52

50

+16

     

confusion (inc. reversals)

32

47

59

+27

     

eyestrain

44

54

44

(=)

     

tiredness (while reading)

25

46

27

+2

     

glare

 

52

 

 

     

Self confidence

33

30

35

+2

     

Perseverance

 

22

40

 

     

Performance (school or career)

 

24 (40)

42 (children:46)

 

     

Depth perception, coordination

 

26

 

 

     

Motion sickness

 

10

 

 

     

* There is an additional degree of subjectivity in this figure. See note on Table 2.

The differences between the 1988 figures and the 1994 figures are slight, except for ease of reading (where 10% more subjects report large improvement after six years than after one year; spelling, where 15% fewer subjects report large improvements; skipping lines or words unintentionally when reading, where 16% more subjects report large improvements; and confusion of letters and words, where 27% more subjects report large improvements. When "some" and "large" improvements are combined, the differences are reduced, as would be expected given the subjective nature of the decision to call an improvement "some" or "large". As well, what seemed a "large" improvement over six months or a year might well be rated as "some" improvement if little further improvement had occurred in the following five or six years. Visual factors still stand out as the areas where lasting improvements are observed. Of those factors surveyed, 8% more subjects reported improvements in tendency to skip lines, 11% more subjects reported improvements in their previous tendency to confuse similar letters and words, and 12% more subjects reported improvements in tiredness when reading. These were the greatest differences.

Discussion

The gains reported by subjects in the earlier study (Whiting & Robinson, 1988) appear to have been maintained over six years. This suggests that it is unlikely that the initial effects were due to placebo alone.

The fact that improvements in visual perception are the factors most often reported after six years of experience with Irlen filters is significant. The development of the skills of written language may be impeded by poor visual perception, but improved perception will not improve the skills themselves. These must be learnt, and, where inappropriate strategies have developed, these must be unlearned. A number of respondents commented that they felt sure that their progress in the acquisition and use of the skills for using written language would have been much greater had they had the filters at a younger age. A number indicated that they had acquired the filters at a time that allowed them to complete important examinations with somewhat greater ease. However, they had subsequently taken up jobs that required little reading or writing in order to avoid having to learn those skills that they had previously found difficult, and that in consequence, they no longer felt need of the filters. Of those who answered the question about how often they wore the filters, only 57% indicated that they wore them always for reading, while 34% said they wore them all the time (presumably because of the difference they made to their perception of space and brightness of light: in Burgessís (1991) study, 41% and 77% respectively indicated improvements in these factors).

Questions were asked about whether any follow-up had been requested at the clinics, whether follow-up was routine or because there had been problems, and whether problems had been resolved. This group of questions proved not to be very useful, as subjects often interpreted problems as meaning "problems at school" such as peer or staff ridicule of children wearing coloured glasses, whereas the question was meant to refer to problems related the filters "not working properly". There was also a question about how much the filters were being worn.

As reported in the earlier study, peer pressure was still a factor in the decision not to wear the filters. This was reported a number of times and has been reported in clinical settings as well. More than one professional working as a consultant indicated that they no longer wore the filters because they were quite dark, and thus inappropriate when talking to clients face-to-face. They would impede eye-contact, which is important to effective consultation, and there could be no more obvious way of drawing attention to a problem than to put coloured glasses on oneís eyes!

Conclusion

The survey reported above supports the results of earlier survey research on the response of people who wear or have worn Irlen filters. The majority of them continue to report benefits of various kinds over a long time span, noticeably in improved visual perception of print, and greater ease of reading. Significant numbers report large improvements in performance of written language skills as well. Only 28% had sought further help through the clinics, a fact that might be open to differing interpretations. However, the reported improvements seem to have taken place without periodic modification of the filters, or advice on other avenues of help. While no questions were asked about other assistance respondents may have obtained for their difficulties, numbers of individual comments indicated that respondents had not had other assistance. This is unfortunate, and may indicate unrealistic expectations of what improved visual perception might do to help poor performance in written language skills. For some, who already possess basic reading skills appropriate to their age, it appears to make a large difference. For others whose basic skills have not been able to develop, improved visual perception could not be expected to make more than a small difference, though it should enhance their ability to learn appropriate skills. This learning has obviously occurred for many subjects, as evidenced by the large positive response to questions concerning improved fluency, accuracy and comprehension in reading. For others, however, the difference may be restricted to clarity of perception and ease of visual processing. This appears to have been the case with a number of subjects.

Whiting & Robinson in their 1988 study indicated that there was a need for "studies designed to show why such a procedure might work, from a physiological standpoint". Such studies are now being done, and it seems there are plausible explanations for the apparent success of the Irlen procedure. Further work is taking place in a number of places on this issue. What seems now to be required is a better integration of clinical intervention using filters and remedial procedures designed to reteach skills that have not been acquired because of perceptual difficulties.

 

References

Aaron, P.G. (1989) Dyslexia and hyperlexia. Dordrecht, Kluwer Academic Publications.

Adler, L. & Atwood M. (1987) Poor readers: what do they really see on the page? A study of a major cause of dyslexia. Calif. Los Angeles County Office of Education.

Burgess, J.E., (1991) Long term evaluations of the effects of Irlen tinted lenses on academic and related areas. Unpublished M.Ed. thesis. University of Canberra.

Chan, L.K.S. & Robinson, G.L.W. (1989) The effects of comprehension monitoring instruction for reading disabled students with and without tinted lenses. Australian Journal of Special Education. 42 (1), 4-13.

Cotton, M.M., & Evans, K.M. (1990), An evaluation of Irlen lenses as a treatment for specific reading disorders Australian Journal of Psychology, 42,1, 1-12.

Fricker, S., (1989) Do Irlen coloured glasses improve stereopsis and reading ability in children who have reading difficulties caused by visual perceptual distortion when they look at black print on white paper, and does their colour vision differ from the normal population? Unpublished Diploma of Community Child Health Thesis, Flinders University (Adelaide) Australia.

Geiger, G. & Lettvin, J.Y.,(1987) Peripheral vision in persons with dyslexia. The New England Journal of Medicine, 316,20, 1238-1243.

Grosser, G.S. & Spafford, C.S.,(1989) Perceptual evidence for an anomalous distribution of rods and cones in the retinas of dyslexics: a new hypothesis. Perceptual and Motor Skills, 68, 683-698.

Irlen, H. (1983) Successful treatment of learning disabilities. Paper presented at the 91st Annual Convention of the American Psychological Association, Anaheim, Calif. August.

Irlen, H. (1991)Reading by the colours: overcoming dyslexia and other reading disabilities through the Irlen method. N.Y. Avery Publishing Group.

Lea, A.R., & Hailey, D., (1991) Tinted lenses in the treatment of the learning disabled. (second edition) Canberra, Australian Institute of health.

Lehmkuhle, S., Garzia, R.P., Turner, L., Hash,T. & Baro, J.A. (1993), New England Journal of Medicine, 328, 14, 989-996.

Livingstone, M.S., Rosen, G.D., Drislane, F.W., & Galaburda, A.M. (1991) Physiological and anatomical evidence for a magnocellular defect in developmental dyslexia. Proceedings of the National Academy of Science USA 88, 7943-7947.

OíConnor, P.D.,Sofo,F.,Kendall, L., Olsen,G., (1990) Reading disabilities and the effect of coloured filters. Journal of Learning Disabilities, 23, 10, 597-603, 620

Robinson, G.L.W. (1990) An evaluation of the Irlen lenses as a treatment for specific reading disorders - commentary on M.M.Cotton and K.M.Evans. Australian Journal of Psychology. 42,1, 13-15.

Robinson, G.L.W., & Conway, R.N.F., (1990) The effects of Irlen coloured lenses on specific reading skills and perception of ability: a twelve-month validity study. Journal of Learning Disabilities, 23, 10, 588-597.

Saint-John, L.M. and White, M.A. (1988) The effect of coloured transparencies on the reading performance of reading disabled children. Australian Journal of Psychology, 40, 403-411.

Solman, R.T., Dain, S.J., & Keech, S.L. (1991) Colour-mediated contrast sensitivity in disabled readers. Optometry and Vision Science, 68 ,5,331-337

Spafford, C., & Grosser, G.S. (1991) Retinal differences in light sensitivity between dyslexic and proficient reading children: new prospects for optometric input in diagnosing dyslexia. Journal of the American Optometric Association. 62, 610-615.

Stanley, G. (1987) Colour filters and dyslexia. Australian Journal of Remedial Education. 19, 8,9.

Stokes,L.D., & Stokes, M.C., (1990) A follow-up on usersí satisfaction with Irlen filters. Irlen Institute Newsletter, 3,4, 3.

Westergard, S. (1993) Colour me literate: the effect of Irlen coloured lenses on visual perceptual distortion. Unpublished M.Ed. project, Northwest Nazarene College.

Whiting, P.R. (1985) "How Difficult can Reading Be? New Insight into Reading Problems" The Teaching of English, 49 October, 49-55.

Whiting, P.R. (1988) Improvements in reading and other skills using Irlen coloured lenses. The Australian Journal of Remedial Education, 20,1, 13-15.

Whiting, P.R. (1993) "How Difficult Can Reading Be?" Parent and Citizen, 44,4, 12-18.

Whiting, P.R. (1993) "Irlen coloured filters: summary of emerging research and indications of help for those appearing to be learning disabled and others," The Bulletin for Learning Disabilities, 3, 1, 66-81.

Whiting. P.R. & Robinson, G.L.W. (1988) Using Irlen coloured lenses for reading: a clinical study. Australian Educational and Developmental Psychologist. 5, 7-

Williams, M.C., Lecluyse K., & Rock-Faucheux, A., (1992) Effective interventions for reading disability. Journal of the American Optometric Association. 63, 6, 411-416.

Winter, S.,(1987) Irlen lenses: an appraisal. Australian Educational and developmental Psychologist. 5, 7-10.