An Investigation of the Visual Function and the Effect of Colored Filters on Reading Ability of Dyslexic Children

Research Article

Austin J Clin Ophthalmol. 2018; 5(2): 1093.

An Investigation of the Visual Function and the Effect of Colored Filters on Reading Ability of Dyslexic Children

Moghaddam HO1,2, Mohammadi Z¹, Yazdani N1,2, Sobhanirad D³, Shandiz JH1,2, Khabazkhoob M4,5 and Ehsaei A1,2*

¹Department of Optometry, School of Paramedical Sciences, Mashhad University of Medical Sciences, Iran

²Refractive Error Research Center, School of Paramedical Sciences, Mashhad University of Medical Sciences, Iran

³Department of Speech Therapy, School of Paramedical Sciences, Mashhad University of Medical, Sciences, Iran

4Noor Research Center for Ophthalmic Epidemiology, Noor Eye Hospital, Iran

5Department of Medical Surgical Nursing, School of Nursing and Midwifery, Shahid Beheshti University of Medical Sciences, Iran

*Corresponding author: Asieh Ehsaei, Assisstant Professor of Optometry and Vision Sciences, Department of Optometry, Mashhad University of Medical Sciences, Parastar 2, Ahmadabad Avenue, Mashhad, Iran

Received: May 01, 2018; Accepted: May 28, 2018; Published: June 04, 2018


Purpose: The aim of the present study was to evaluate the effect of colored filters on the reading ability in dyslexic children.

Method: Twelve children with dyslexia and twelve age and gender matched non-dyslexic children between second and fifth grade were recruited. Visual acuity assessment, refraction and binocular examinations including far and near heterophoria, near point of convergence and accommodation, stereopsis, and near fusional reserves were performed for all participants. Afterwards, both the colored filters and transparent ones were used in dyslexic group. Children were asked to choose one filter which enhances the clarity or perception of the text and then the reading ability was measured with and without filters.

Results: The mean age of all subjects was 8.42±1.06 years. The results showed that fusional reserves significantly reduced in dyslexic children compared to normal individuals, although no statistically significant difference was reported in other visual functions. Moreover, it has been shown that reading ability of dyslexic children was significantly improved with colored filters.

Conclusion: The results of the present study showed that fusional reserves decreased in dyslexic children. Moreover, speed and accuracy of the reading increased significantly in dyslexic children with color filters. It would be recommended that in dyslexic children, in addition to a thorough assessment of binocular vision, using color filters is beneficial.

Keywords: Dyslexia; Binocular vision; Magnocellular system; Colored filters; Colored overlays


Reading and writing are the most important issues for learning especially in today’s computer-based society. Any disorder or disability which affects children proficiency to read or write is classified as a learning disability and may result in negative effects on educational, emotional and either social functions [1,2]. One of the most common learning disabilities is dyslexia which is characterized with debility in reading [2-4]. It has been estimated that 3% [5] to 13.67% of school-aged children are dyslexic [6]. Considering the visual system, significant association have been found between magnocellular pathway involvement and dyslexia incidence [7,8]. The main hypothesis for this association is magnocellular theory, according to which most of children with dyslexia have defect in magnocellular pathway [9]. Moreover, it has been agreed that any disorder in eye movement could be a leading cause for dyslexia [10]. Binocular instability is the most common visual sign in dyslexic patients, which is distinguished by the low fusional reserve and vergence instability [11]. Patients with binocular instability usually suffer from blur vision, diplopia, asthenopia and visual distortion [12]. Kriss and Evan reported that visual stress, which was defined as any disability to see comfort and without distortion, is more prevalent in dyslexic children compared with normal population [13].

It has been approved that decreasing the font size, using colored filters and reducing the contrast could improve the reading ability in dyslexic patients, and relieve visual symptoms through increasing patient’s perception [1,14]. Color filters, was firstly introduced by Irlen International Association [15], who suggested applying filters as an effective remedy for visual symptoms-co-occurring dyslexia and stated that the color of the therapeutic filter is different from person to person, therefore, it may not have any effect if an appropriate color does not prescribed [16]. According to previously published studies, colored filters or overlays could improve the symptoms of visual stress and reduce the asthenopia symptoms and consequently improve the reading ability in dyslexic children [17-19]. This study is proposed to assess the effectiveness of colored filters on reading speed in dyslexic children.


Study population

Twelve dyslexic children and twelve age- and gender- matched normal individuals (age range: 7 to 10 years of age) were recruited for this study according to inclusion criteria as follows: normal mean intelligence quotient between 90 and 110 (Wechsler intelligence test), being healthy without any physical problems, parents’ consent, lack of acute vision and hearing problems and no psychological problems. Children with any ocular pathology were excluded from the study population. All patients were referred by a specialist to the dyslexia comprehensive center. It is important to keep in mind that dyslexia is not a disease or an identifiable physical condition. Rather, it is a learning style that could be assessed through a profile to show whether the child has a typical pattern of strengths and weaknesses, coupled with other assessments to rule out other possible causes of symptoms, such as vision or hearing problems.

A diagnostic assessment is the most comprehensive kind of assessment. Definitive diagnosis of dyslexia has been confirmed using psychological tests, math performance tasks, sequential memory tests, cognitive and emotional growth tests and also speech therapy examination. All tests were performed by an experienced psychologist. Patients with any history of dyscalculia, attentiondeficit/ hyperactivity disorder, attention deficit disorder, ocular pathology, and amblyopia or color vision deficient were excluded from the study. Demographic data were collected for each subject and detailed visual examinations were performed including: visual acuity, refractive error, distance and near heterophoria, positive and negative fusional reserves and depth of vision.

Ethical consideration

Informed consent of a parent/guardian was obtained after explanation of the nature and possible consequences of the study. The experiment followed the tenets of the Declaration of Helsinki and was approved by the Research Ethics Committee of Mashhad University of Medical Sciences.

Visual function assessment

Subjective and objective refractions were carried out using retinoscope (Heine Beta 200 retinoscope, HEINE Optotechnic, Germany, and auto refractometer (Topcon RM8800, Topcon Corporation, Japan, Visual acuity was measured monocularly with the Snellen chart at a distance of 6m. The cover test was done to confirm the presence of any far or near heterophoria and simultaneous prism and cover test was performed to estimate the amount of present heterophoria.

For assessment of the near point of accommodation, the correction was cited in trial frame and normal room illumination was used. Each patient observed the target at a distance of 40cm and was instructed to report the first sustained blurred, then the measured distance from the spectacle plane was converted to dioptric power. The same procedure was repeated for assessment of the near point of convergence, while the patient was instructed to report the first diplopic image of the target. All measurements were repeated for three times and average was recorded.

Positive and negative fusional reserves were evaluated using the prism bar at 40cm. Divergence or negative ranges (Base In) were tested before convergence or positive ranges (Base Out) due to possible vergence adaptation. For each section, the patient was instructed to report the blur, break and recovery of the target while adjusting the prism power.

Stereoacuity was measured in subjects using the Titmus circles test (Stereo Optical, Chicago, IL).

Reading ability

Reading ability was measured with the Decoding Skills Test (DST), which contains 10 experiments [20]. Reading ability was evaluated using three of sub tests including: reading words, reading non-words and chain of words. Hoseini et al [21] approved the validity and reliability of the reading tests. Total test time was 2 minutes. Each correct answer had one score and the highest score was 30. Raw scores are used to convert results into grade- level scores. Additionally, level score shows how the patient performs and if he or she could proceed to the next level. Thirteen filters with different colors and intensity, which were defined using UV Visible Spectrophotometer, were used. Table 1 shows the physical characteristic of each filter. Wilkins method was used to choose filters [22]. Reading skill was evaluated with and without filters. The current study was a blind study and information about the efficacy of filters was masked from the participants to eliminate the bias until after a trial outcome was known.