Introduction
Dyslexia is a learning disorder that affects reading, writing, and spelling skills. It is estimated to affect around 5 to 10% of the population and often runs in families. Dyslexia is a neurological condition affecting how the brain processes written language. On the other hand, binocular vision refers to using both eyes in coordination to form a single, three-dimensional image. It is an essential aspect of visual perception, and it helps us to perceive depth and distance accurately.1 Itaffects many factors, including eye movements, eye alignment, and the ability of the brain to fuse images from both eyes into a single, coherent picture.2
Research has shown that there may be a connection between dyslexia and binocular vision problems. Research suggests that people with dyslexia may also struggle with binocular vision, such as eye tracking, eye teaming, and convergence.3 These difficulties may contribute to the reading difficulties experienced by individuals with dyslexia. However, the association between dyslexia and binocular vision problems is complex, and significant research is required to understand it fully.4 Some researchers have suggested that binocular vision problems may be a consequence of dyslexia rather than a cause. In contrast, others have proposed that underlying neurological factors may cause both conditions.5 Despite the lack of consensus, it is clear that addressing binocular vision problems can improve reading performance in some individuals with dyslexia, and this area continues to be an active area of review of literature interest.
Accommodation & vergence function in children with dyslexia
Inspected investigations revealed poor monocular accommodative amplitudes and the binocular accommodative capability, which is optical power it can achieve by changing its focus. Low Negative relative accommodation (NRA) and positive relative accommodation (PRA), where NRA Measures the most outstanding accommodation relaxing capacity while preserving unobstructed, single-binocular vision and PRA Measures the most remarkable accommodation-stimulating capacity while preserving clear, single-binocular vision values, which are categorized as accommodative insufficiency which in turn results in asthenopic symptoms. Symptom reduction and improved focus may be achieved with therapy, including lens adjustments and accommodative training.6, 7 Decreased vergence reserve amplitude at near, demonstrating reduced distance base-in (NFV) vergence, inadequate vergence control, unstable binocularities, and restricted divergence at both far and near distances.8, 9, 10 Divergence deficits can occur irrespective of convergence and accommodation relaxation, and their appearance at a distance suggests that they do. The physiological studies showing different convergence and divergence modulations at the cortical and subcortical premotor levels support this unexpected finding. Many studiesreveal vergence deficiencies, typically prevalent in people with dyslexia. So, the treatment should specifically target the convergence and divergence subsystems.10 Motor deficiencies are directly related to dyslexia-related functions.11
For those who have dyslexia, these deficiencies will make life more difficult, but they are also easily remedied. Eye care professionals should take several measurements when examining people with dyslexia since it is crucial to spot refractive, accommodative, or binocular irregularities in populations with dyslexia.12 The findings confirm that dyslexia's phonological deficit are not its underlying cause rather is the cause of the recent discoveries of binocular impairments in dyslexic children.2
Therefore, the eye care practitioner must perform a binocular vision evaluation on all children, especially those with reading difficulties. In order to ensure proper diagnosis and treatment for school-aged children who have been identified as having a reading problem, a comprehensive eye examination should include tests for binocular vision and accommodative status, such as near point of convergence (NPC), accommodative facility, amplitude of accommodation, and fusional ranges.13
Objectives
Clinicians and educators need to understand how to diagnose and treat dyslexia and associated vision problems. This review article can provide valuable insights into practical assessment and intervention strategies by summarizing the latest research on these topics. Additionally, this review article can help to identify areas where more research is needed. While there has been some research on the connection between dyslexia and binocular vision, much is still not fully understood. A review article can guide future research efforts by highlighting these gaps in knowledge. Overall, a review article on dyslexia and binocular vision can be a valuable resource for researchers, clinicians, educators, and anyone interested in understanding these conditions and how they may be related.
Rational
This review paid much attention to the literature about binocular vision parameters in kids with dyslexia worldwide. A study has yet to present an all-encompassing perspective together. Nevertheless, with the assistance of a thorough literature study, we will provide an all-encompassing perspective on the binocular vision parameters in children with dyslexia and its significance in clinical practice in this review.
Materials and Methods
In this part, we will cover the approach used to conduct a literature review to investigate the accommodative and vergence parameters among children with dyslexia.
Eligibility criteria
The literature associated with any binocular vision parameters in children with dyslexia around the globe was given a significant amount of focus in this study. The approach involved examining papers from conferences as well as journal articles, and it also involved initial studies that showed alterations in binocular vision parameters. Our search focused on articles that address visual acuity, stereoacuity, accommodative and vergence parameters in dyslexic children, as these are crucial components of adequate vision during reading. Studies on dyslexia-related psychological and behavioral alterations, however, were not included. Articles in all languages were considered and translated into English using autoML translation. Much research done and published during 1991 to 2022 on visual deficits and dyslexia were used to inform this study and the age group of the children were considered between 6 -15 years.
Search strategy
Original and review papers were searched on research repositories including PubMed, Ovid, and Google Scholar. Visual deficits, accommodative inertia, the amplitude of accommodation, near point of accommodation, near point of convergence, fusional vergence, and stereopsis in children with dyslexia were keywords that were included throughout the search. Based on the title and abstract, an initial evaluation was conducted. Selected pieces were thoroughly examined before being included.
Data extraction
The inclusion applied was binocular vision parameters among children with dyslexia, and the studies related to syndrome and learning disabilities other than dyslexia, disease, and dyslexia, as well as studies with no baseline screening, were excluded. Relevant titles and abstracts were examined. The selected studies were evaluated using a data extraction form that included variables like first author, country, age, gender, and characteristics of dyslexia patients. Outcomes were categorized based on visual criteria evaluations.
Data synthesis
To provide a qualitative analysis of the included study's findings and components, the information acquired from the relevant research is summarized in the form of tables manually. Investigations of Accommodation & Vergence function in the dyslexic and typical children were compared. Literature management program, Mendeley was used for the evaluation of each study's excellence.
Study risk of bias assessment
The quality of the included papers was assessed using the ROBINS-I approach for non-randomized trials.14 Within this approach, the evaluation covered seven distinct themes: confounding, participant selection for the study, classification of interventions, deviations from intended interventions, missing data, assessment of outcomes, and selection of reported results. These themes were thoroughly examined to ensure a comprehensive analysis of potential biases, all while maintaining originality in the write-up.
Results
Study selection and characteristics.
Selection process
One thousand two hundred-five articles were identified in the initial search strategy for all keywords. Twenty-three duplicates and 562 articles were removed for other reasons, and 620 articles were screened. The abstract of 620 articles was inspected, out of which 548 were excluded, and the intention for exclusion is mentioned in the flow diagram strictly following the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines (Figure 1 ). 15 All 18 articles were focused on and included. All the Study Design, Characteristics and Risk of bias assessment are summarized in (Table 1).
Result outcomes
Effect on visual acuity
Visual acuity, when compared between dyslexic and normal child population studies showed no significant differences in distance visual acuity.12, 2, 13, 3, 16 Whereas studies showed a notable distinction in the near visual acuities of the compared groupswhich has been summarized in (Table 2).12, 3, 17
Table 1
Study design, characteristics and risk of bias assessment
|
Author |
Year |
Age |
Sample size |
Study design |
Limitation |
Country |
ROBINS-I |
|
Borsting et al. 6 |
2003 |
8–15 |
392 Typical Readers |
Cross-sectional study |
It is important to evaluate the matched group taking into account other factors such as screen time. |
California |
High |
|
Catalina Palomo-Álvarez et al. 8 |
2010 |
8-13 |
87 Poor readers 32 Controls |
Cross-sectional study |
The study should assess the impact of vision therapy on reading tasks for children with poor reading skills. |
Spain |
Moderate |
|
Buzzelli, Andrew R. 11 |
1991 |
13 |
13 Dyslexics 13 Normal readers |
Cross-sectional study |
………………………… |
|
High |
|
Zoï Kapoula et al. 10 |
2007 |
10.7±2 |
57 Dyslexics 46 non-dyslexics |
Cross-sectional study |
Research in this field should combine orthoptic tests, visual training, and recordings of eye movements during reading before and after orthoptic training. |
Paris, France |
Moderate |
|
Gro Horgen Vikesdal et al. 12 |
2019 |
9-12 |
17 Dyslexics 17 Controls |
Experimental study |
It is possible that the high prevalence of hypermetropia in the dyslexic group is due to a small sample size, which could have been affected by the inclusion of more males than females. |
Norway |
Moderate |
|
Wahlberg-Ramsay et al. 2 |
2012 |
13.8 ± 1.33 14.2 ± 1.67 |
63 Dyslexics 60 controls |
cross-sectional study |
………………………….. |
Sweden |
Moderate |
|
Lisa W. Christian et al. 13 |
2017 |
8.6 ± 2.3 |
121 Poor readers |
Descriptive study |
All children from different schools should be included in the study. Randomized controlled trials should be conducted to determine if treating binocular vision conditions can significantly improve children's reading ability. The study should also incorporate additional tests for saccadic eye movements, such as an eye tracker. |
Canada |
Moderate |
|
Jan Ygge et al18 |
1993 |
7- 9 |
86 Dyslexics 86 controls |
Longitudinal study |
…………………………. |
Sweden |
Moderate |
|
Wajuihian SO et al. 3 |
2011 |
13 ± 1.42 11.9 ± 0.93 |
31 Dyslexic Children 31 Controls |
cross-sectional study |
…………………………. |
|
High |
|
Bruce J. W. Evans et al. 17 |
1994 |
8-15 |
39 Dyslexic Children 43 controls |
cross-sectional study |
………………………… |
London |
High |
|
Azam Darvishi et al. 16 |
2022 |
8.1 ± 0.8 |
32 children with dyslexia |
Randomized, observational study |
Result: Discovered a strong association between the degree of dyslexia and higher near exophoria. |
Mashhad, Iran |
Moderate |
|
Aparna Raghuram et al.19 |
2018 |
7-11 |
29 Developmental Dyslexia 33 Typical Developing |
A prospective, uncontrolled observational study |
Small sample size and unmasked examiners not amenable to examiner bias or influence. |
Boston |
Moderate |
|
Hayes et al.20 |
1998 |
Kindergarten |
297 |
Randomized, Prospective study |
Further study with same standardized NPC method should be implemented with Symptomology questionnaire |
California |
Moderate |
|
Third grade |
|||||||
|
Sixth grade |
|||||||
|
Borsting et al.21 |
1999 |
8–13 |
14 (CI) 14 (Normal) |
Case control study |
Standardized symptom Survey or Questionnaires can be used to know the efficacy of different modes of treatments |
California |
Moderate |
|
Ramsay et al. 22 |
2012 |
13.80 ± 1.33 |
63 children with dyslexia |
cross-sectional study |
………………………….. |
Sweden |
High |
|
14.25 ± 1.67 |
60 Controls |
||||||
|
Wolfgang Dusek et al.5 |
2010 |
6-12 |
810 poor readers 308 controls |
Retrospective clinical study |
More research is necessary on binocular vision problems in school children with poor reading skills beyond Europe. |
Austria |
Moderate |
|
M-L Latvala et al. 23 |
1994 |
9-10 |
82 Dyslexics 84 controls |
cross-sectional study |
Large sample size and an extended treatment time. Furthermore, a reading comprehension test that measures actual comprehension improvement would be interesting to include. |
Finland, Europe |
Moderate |
|
Catalina Palomo-Álvarez et al. 24 |
2008 |
8-13 |
87 poor readers 32 controls |
cross-sectional study |
It is necessary to study how accommodative treatments affect the reading performance of young readers with low skills. |
Spain |
Moderate |
Table 2
Visual acuity among dyslexic and control group
|
Author |
Sample size |
Age (Mean±SD) |
Method |
Visual AcuityOD/OS/OU (Mean±SD) |
P- value |
|
Gro Horgen Vikesdal et al. 201912 |
27 children with dyslexia |
10.4 ± 1.3 |
Distance Visual acuity (LogMAR) Near Visual acuity (LogMAR) |
OU: 0.09 ± (0.07) OU: 0.03 ± (0.05) |
>0.05(Distance) |
|
27 Controls |
10.0 ± 1.1 |
Distance Visual acuity (LogMAR) Near Visual acuity (LogMAR) |
OU: 0.06 ± (0.08) OU: 0.01 ± (0.04) |
0.029(Near) |
|
|
Wajuihian SO et al. 20113 |
31 children with dyslexia |
13 ± 1.42 |
Distance Visual acuity (LogMAR) |
OD:0.17 ± 0.31 OS:0.20 ± 0.33 |
OD:0.29 (Distance) |
|
31 controls |
11.90 ± 0.93 |
Distance Visual acuity (LogMAR) |
OD: 0.00 ± 0.24 OS: 0.00 ± 0.24 |
OS: 0.23 (Near) |
|
|
Bruce J. W. Evans et al. 1994 17 |
39 children with dyslexia |
9.5±2.5 |
Near Visual acuity (LogMAR) |
Worse in the dyslexic group (Mann-Whitney U-test,) |
0.0018 |
|
43 controls |
9.1±1.8 |
||||
|
Wahlberg-Ramsay et al. 201212 |
63 children with dyslexia |
13.80 ± 1.33 |
Distance Visual acuity (EDTRS chart at 4 m) Near Visual acuity (EDTRS-like chart at 33 cm) |
OD: 1.25 ± 0.30 |
>0.05 (distance and near) |
|
OU: 1.30 ± 0.3 |
|||||
|
OD: 0.86 ± 0.10 |
|||||
|
OU: 0.95 ± 0.08 |
|||||
|
|
60 controls |
14.25 ± 1.67 |
Distance Visual acuity (EDTRS chart at 4 m) Near Visual acuity (EDTRS-like chart at 33 cm) |
OD: 1.20 ± 0.21 |
|
|
OU: 1.31 ± 0.43 |
|||||
|
OD: 0.92 ± 0.12 |
|
||||
|
OU: 1.03 ± 0.10 |
|||||
|
Lisa W. Christian et al. 2017 13 |
121 Poor readers |
8.6 ± 2.3 |
Distance Visual acuity (LogMAR) |
OD:0.04 ± 0.11 |
……………… |
|
OS:0.03 ± 0.11 |
|||||
|
OU: 0.00 ± 0.08 |
|||||
|
Near Visual acuity (LogMAR) |
OD:0.03 ± 0.21 |
||||
|
|
OS:0.03 ± 0.20 |
|
|||
|
|
|
|
|
OU:0.03 ± 0.20 |
|
|
Azam Darvishi et al. 202216 |
32 children with dyslexia |
8.1 ± 0.8 |
Distance Visual acuity (LogMAR) |
OD:0.002±0.011 |
|
|
OS:0.004±0.018 |
……………….. |
||||
|
|
|
|
|
OU:0.002±0.011 |
|
Table 3
Stereo acuity among dyslexic and control group
|
Author |
Sample Size |
Age(Mean±SD) |
Stereoacuity (Mean±SD) |
P-Value |
|
Buzzelli, Andrew R. (1991)11 |
13 Normal readers |
13±1.9 |
24±8.77 |
0.677 |
|
13 Children with dyslexia |
13±1.5 |
23.46±15.46 |
||
|
Bruce J. W. Evans et al. (1994) 17 |
43 Normal readers |
9.5±2.5 |
20 (median) |
>0.05 |
|
38 Children with dyslexia |
9.1±1.8 |
25 (median) |
||
|
Azam Darvishi et al. 2022 16 |
32 children with dyslexia |
8.1 ± 0.8 |
Mild dyslexia: 138.33±100.56 |
0.998 |
|
|
|
|
Moderate dyslexia:57±9.48 |
|
|
|
|
|
Severe Dyslexia:106.15±78.05 |
|
|
Catalina Palomo-Álvarez et al. 2010 8 |
87 Poor readers |
10.5±1.7 |
25.2±11.3 |
>0.05 |
|
32 Normal readers |
10.2±1.5 |
32 23.8±8.6 |
||
|
Monireh Feizabadi et al. 201825 |
27 Children with dyslexia |
10±2.5 |
14.8% of dyslexic group worse than 60 s of arc |
0.785 |
|
40 Normal readers |
10±2.5 |
12.5% of control group worse than 60 s of arc |
||
|
Gro Horgen Vikesdal et al. 2019 12 |
17 Dyslexics |
Children with dyslexia (Children were between 4th and 6th grade) |
60.00 ± (17.82) |
0.018 |
|
17 Controls |
Control (Children were between 4th and 6th grade) |
45.00 ± (16.27) |
||
|
Zoï Kapoula et al. 200710 |
57 dyslexics |
10.7±2 |
<60″ (21%) |
|
|
|
|
60″ (78%) |
>0.05 |
|
|
|
|
>60″ (1%) |
|
|
|
46 non-dyslexics |
10.7±2 |
<60″ (31%) |
|
|
|
|
|
60″ (69%) |
|
|
|
|
|
|
>60″ (0%) |
|
|
M-L Latvala et al.199423 |
82 dyslexics |
9±0.4 |
>60 seconds of arc (9.1%) |
>0.05 |
|
|
84 controls |
9±0.5 |
>60 seconds of arc (8.0%) |
|
Table 4
NPC among dyslexic and control group
|
Author |
Sample Size |
Age (Mean±SD) |
Method |
Breakpoint/ Recovery point (Mean±SD) |
P-Value |
|
Catalina Palomo-Álvarez et al.20108 |
87 Poor readers |
10.5±1.7 |
Penlight push-up technique (three measurements by the same examiner) |
3.7±3.2 / 9.1±5.2 |
>0.05 |
|
32 Controls |
10.2±1.5 |
4.3±2.3 / 7.9±3.2 |
|||
|
Ramsay et al. 2012 22 |
63 children with dyslexia |
13.80 ± 1.33 |
The Royal Air Force (RAF) rule |
5.80 ± 1.85 (breakpoint) |
<0.001 |
|
|
60 Controls |
14.25 ± 1.67 |
|
6.10 ± 2.10 (breakpoint) |
|
|
Jameel Rizwana Hussaindeen et al.201826 |
20 No NSBVA Poor readers |
15 ±2.1 |
Push-up with the accommodative task (three measurements) |
7±2.5/ 8 ±0.9 |
0.005 |
|
46 NSBVA Poor readers |
15 ±2.1 |
9±2.3 / 10±2.25 |
|||
|
Gro Horgen Vikesdal et al. 201912 |
17 children with dyslexia |
Children were between 4th and 6th grade |
Push-up with the accommodative task (three measurements) |
6.47 ± (2.06) (break) |
>0.05 |
|
17 Controls |
Children were between 4th and 6th grade |
5.56 ± (1.28) (break) |
|||
|
Wajuihian SO et al. 20113 |
31 Dyslexic Children |
13 ± 1.42 |
Push-up with accommodative task (three measurements) |
8.90 ± 5.03 cm/ 14 ± 5.88 cm |
0.049 (break) |
|
31 Controls |
11.90 ± 0.93 |
12.60 ± 8.70 cm/ 22 ± 8.20 cm |
0.06 (recovery) |
||
|
Monireh Feizabadi et al. 2018 25 |
27 Children with dyslexia |
10±2.5 |
push-up technique using an accommodative target (single 20/30 letter). |
5.25 ± 1.36 |
0.33 |
|
4.95 ± 1.17 |
|||||
|
|
40 Controls |
10±2.5 |
|
|
|
|
Wolfgang Dusek et al. 2010 5 |
801 Poor readers |
9±3 |
Penlight push-up technique (three measurements by the same examiner) |
4.74 ± 5.59 (break) |
< 0.001 |
|
|
324 controls |
9±2.5 |
|
3.41 ± 4.62 cm (break) |
|
|
Zoï Kapoula et al. 200710 |
57 dyslexics |
10±2.5 |
Penlight push-up technique |
<6cm (break): 44% =6 cm (break):14% |
<0.01 |
|
|
|
|
|
7-10cm(break):36% >10 cm(break): 6% |
|
|
|
46 non-dyslexics |
10.7±2 |
|
<6cm (break): 72% =6 cm (break):13% |
|
|
|
|
|
|
7 10cm(break):15% >10 cm(break): 00.0 |
|
|
Aparna Raghuram et al. 2018 19 |
29 Developmental Dyslexics |
10.3± 1.2 |
Push-up with accommodative target |
8.00±2.6 /10.57±2.96 |
0 .01 |
|
|
33 Typically developing readers |
9.4± 1.4 |
|
6.30±1.57/ 8.33±1.71 |
|
Table 5
Fusional vergence system among dyslexic and control group
|
Author |
Sample Size |
AgeMean±SD |
Fusional Vergence Amplitude (Mean±SD) |
P-Value |
|
|
|
|
|
Distance |
Near |
|
|
Catalina Palomo-Álvarez et al.2010 8 |
87 poor readers |
10.5±1.7 |
BI Break: 9.1±3.0 BI Recovery: 3.6±1.9 BO Blur: 14.2±6.7 BO Break: 19.0±8.3 BO Recovery: 6.0±4.1 |
BI Blur: 13.0±3.8 BI Break: 18.8±4.7 BI Recovery: 8.9±3.3 BO Blur: 18.8±4.6 BO Break: 26.3±7.7 BO Recovery: 12.2±7.1 |
(BI- break) = 0.001 (BI recovery) >0.05 |
|
|
32 control children |
10.2±1.5 |
BI Break: 11.1±3.4 BI Recovery: 5.0±2.4 BO Blur: 11.4±6.0 BO Break: 17.8±6.1 BO Recovery: 7.9±3.5 |
BI Blur: 11.5±6.6 BI Break: 17.6±5.7 BI Recovery: 9.0±4.45 BO Blur: 18.7±7.8 BO Break: 25.1±7.2 BO Recovery: 12.4±4.8 |
|
|
Jan Ygge et al 1993 18 |
86 dyslexics |
2nd & 3rd grade children |
BI Break: 6.5±3 BO Break: 16.8±5.3 |
BI Break: 10.5±2.9 BO Break: 26.5±6.8 |
>0.05 |
|
|
86 controls |
2nd & 3rd grade children |
BI Break: 6.2±2.6 BO Break: 16.8±6.5 |
BI Break: 10.2±3.2 BO Break: 26.3±7.2 |
|
|
Wahlberg-Ramsay et al. 2012 2 |
63 children with dyslexia |
13.80 ± 1.33 |
BI Break: 10.42 ± 4.46 BO Break: 18.05 ±8.11 |
BI Break: 11.41 ± 3.49 BO Break: 24.56± 8.43 |
>0.05 |
|
60 controls |
14.25 ± 1.67 |
BI Break: 9.87± 3.85 BO Break: 19.00± 6.41 |
BI Break: 12.16 ± 4.57 BO Break: 23.84± 9.16 |
||
|
Lisa W. Christian et al. 201713 |
121 Poor readers |
10±4 |
BI Break: 9.41 ± 5.17 BI Recovery:7.44 ± 6.68 BO Break:20.86 ± 10.31 BO Recovery:13.05 ±6.5 |
BI Break: 13.44 ± 6.40 BI Recovery: 9.77 ± 5.36 BO Break: 21.54 ± 12.37 BO Recovery:15.1 ±8.44 |
______ |
|
Aparna Raghuram et al. 201819 |
29 Developmental Dyslexics |
10.3± 1.2 |
BI Break: 6.71±0.36 BI Recovery: 4.20±0.34 BO Break: 18.36±1.61 BO Recovery: 12.12±0.93 |
BI Break: 11.31±3.13 BI Recovery: 8.28 ±3.19 BO Break: 28.72 ±7.71 BO Recovery: 22.10± 6.25 |
>0.05 (Distance) 0.01 (Near) |
|
|
33 Typically developing readers |
9.4± 1.4 |
BI Break: 7.31±0.32 BI Recovery: 4.86±0.30 BO Break: 16.96±1.44 BO Recovery: 11.12±0.83 |
BI Break: 11.70 ±2.92 BI Recovery: 8.55±2.88 BO Break: 32.97±7.40 BO Recovery: 26.39±7.13 |
|
|
Bruce J. W. Evans et al. 199417 |
24 Dyslexic |
9.5±2.5 |
BI Blur: 9.5±4.5 BI Break: 14.2 ±5.4 BI Recovery: 9.1 ±5.3 BO Blur: 10.9±5.4 BO Break: 15.4±6.7 BO Recovery: 9.5 ±6.5 |
……………. |
0.0084 (Break) |
|
|
Control 19 |
9.1±1.8 |
BI Blur: 14.2 ±7.4 BI Break: 16.1 ±6.2 BI Recovery: 11.6 ±7.0 BO Blur: 16.7 ±9.6 BO Break: 19.0±7.8 BO Recovery: 12.3 ±8.1 |
…………………. |
0.026 (Recovery) |
|
Wajuihian SO et al. 20113 |
31 dyslexics |
13 ± 1.42 |
BI Break:14.69 ±6.83 BI Recovery:11.72 ±6.20 BO Break: 27.06±9.25 BO Recovery: 18.76±7.96 |
BI Break: 11.85±5.14 BI Recovery: 8.77±4.78 BO Break: 21.60±11.62 BO Recovery: 13.35±7.45 |
0.49 (Distance) |
|
|
31 controls |
11.90 ± 0.93 |
BI Break: 16±3.5 BI Recovery: 12.80±3.17 BO Break: 24.16±9.75 BO Recovery: 17±6.93 |
BI Break:12.83 ±3.13 BI Recovery: 1032±3.35 BO Break:21.09 ±8.42 BO Recovery: 15.55±6.25 |
0.17 (Near) |
|
Gro Horgen Vikesdal et al. 2019 12 |
17 children with dyslexia |
10.4 ± 1.3 |
…………………………….. |
BI Break: 8.24 ± (3.21) |
0.006 |
|
17 Controls |
10.0 ± 1.1 |
……………………………… |
BI Break: 11.53 ± (3.18) |
||
Effects on stereo acuity
In most studies11, 17, 16, 8, 25, 10, 23 Significance was not found, but a study12 showed significant differences in the stereo acuities of dyslexic and normal children with the age group between 4th and 6th grade, but the values were still found to be in the normal range hence Dyslexia shows no significant effect on stereopsis; evidence of all the studies is compiled in (Table 3 ).
Effects on NPC
(Table 4 )showing a notable difference in many studies on NPC in dyslexic population.10, 3, 20, 21, 22, 5, 19, 26 A possible explanation for these difficulties could be that dyslexia is associated with underlying neurological and cognitive differences. These differences may include problems with visual processing and attention. However, some studies have shown no significant results.8, 12, 25
Effect on fusional vergence system
(Table 5 ) compiling the studies on fusional vergence, which can affect their ability to read and focus on near objects noted that various research.8, 12, 17, 19 has suggested that some children with dyslexia may have difficulties with fusional vergence, whereas some studies denied the same.18, 2
Effect on accommodative facility
(Table 6 ) presents a summary of the accommodative facility parameters noted in several studies. The studies by19, 3, 5, 24 found significant statistical differences in the accommodative facility. However, the study by12 did not observe any statistical differences.
Table 6
Accommodative facility among dyslexic and control group
|
Author |
Sample Size |
Age (Mean±SD) |
BAF/MAF (Cycle Per Minute) (Mean±SD) |
P-Value |
|
Lisa W. Christian et al. 2017 13 |
121 Poor readers |
8.6 ± 2.3 |
OD: 9.15 ± 3.24 |
|
|
|
|
OS: 9.53 ± 3.54 |
>0.05 |
|
|
|
|
OU: 9.35 ± 3.84 |
|
|
|
Aparna Raghuram et al. 2018 19 |
29 Developmental Dyslexics |
10.3± 1.2 |
5.26±2.79/4.89±2.94 |
< .001 (MAF) |
|
33 Typically developing readers |
9.4± 1.4 |
6.97±3.24/7.27±2.52 |
>0.05 (BAF) |
|
|
Wajuihian SO et al. 20113 |
31 Dyslexic Children |
13 ± 1.42 |
6.86 ± 2.74 |
= 0.03 |
|
31 Controls |
11.90 ± 0.93 |
8.85 ± 3.69 |
|
|
|
Wolfgang Dusek et al. 20105 |
810 poor readers |
9±3 |
6.51 ± 3.83 |
< 0.01 |
|
308 controls |
9±2.5 |
9.00 ± 3.46 |
|
|
|
Gro Horgen Vikesdal et al. 2019 12 |
17 Dyslexics |
Children with dyslexia (Children were between 4th and 6th grade) |
6.41 ± (3.61) |
>0.05 |
|
|
17 Controls |
Control (Children were between 4th and 6th grade) |
7.06 ± (3.21) |
|
|
Catalina Palomo-Álvarez et al. 200824 |
87 poor readers |
10.5±1.7 |
4.9±3.1 |
<0.001 (MAF) < 0.05 (BAF) |
|
32 controls |
10.2±1.5 |
6.3±2.9 |
||
Effect on amplitude of accommodation
In some studies.19, 25, 27, 5 amplitude of accommodation was observed to be significantly decreased in dyslexic group in comparison with normal child population group and contrasting results were seen in other studies where no difference was seen. 22, 17, 24, 3, 16 altogether studies are compiled in (Table 7 ).
Table 7
Amplitude of accommodation among dyslexic and control group
|
Author |
Sample Size |
Age (Mean±SD) |
Amplitude of Accommodation (Mean±SD) |
P-Value |
|
Ramsay et al. (2014)22 |
63 children with dyslexia |
13.80 ± 1.33 |
Monocular (OD): 12.09D ± 2.65 Binocular: 13.10D ± 2.34 |
>0.05 |
|
60 Controls |
14.25 ± 1.67 |
Monocular (OD): 13.30D ± 3.24 Binocular: 14.42D ± 2.10 |
||
|
Bruce J. W. Evans et al. (1994)17 |
39 children with dyslexia |
9.5±2.5 |
OD: (Median)14.0 |
> 0.10 |
|
OS: (Median) 13.9 |
||||
|
OU: (Median)16.0 |
||||
|
43 controls |
9.1±1.8 |
OD: (Median)16.8 |
||
|
OS: (Median) 18.0 |
||||
|
OU: (Median)20.0 |
||||
|
Aparna Raghuram et al. 201819 |
29 Developmental Dyslexia |
10.3± 1.2 |
Binocular: 10.18D ± 1.99 |
< .001 |
|
33 Typical Developing |
9.4± 1.4 |
Binocular: 11.77D ± 1.42 |
||
|
Monireh Feizabadi et al.201825 |
27 Children with dyslexia |
10±2.5 |
OD: 6.90 ± 1.23 cm (NPA) |
|
|
OS:7.32 ± 1.68 cm (NPA) |
0. 049 |
|||
|
OU: 6.66 ± 1.21 cm (NPA) |
||||
|
40 Controls |
10±2.5 |
OD: 5.98 ± 1.15 cm (NPA) |
||
|
|
OS:6.23 ± 1.20 cm (NPA) |
|||
|
OU: 6.00 ± 1.38 cm (NPA) |
||||
|
Catalina Palomo-Álvarez et al. 200824 |
87 poor readers |
10.5±1.7 |
Monocular AOA OD: 9.1±2.3 |
>0.05 |
|
Monocular AOA OS: 9.0±2.3 |
||||
|
32 controls |
10.2±1.5 |
Monocular AOA OD: 10.5±1.7 |
||
|
Monocular AOA OS: 10.5±1.8 |
||||
|
Kristen Kerber et al. 2017[27 |
30 dyslexic individuals |
10.29±1.17 |
Binocular: 10.21± 2.04 |
0.05 |
|
33 typically reading children |
9.44±1.38 |
Binocular: 11.5±1.48 |
||
|
Wajuihian SO et al. 20113 |
31 Dyslexic Children |
13 ± 1.42 |
OD: 11.98 ± 2.34 D |
|
|
OS: 12.14 ± 2.15 D |
>0.05 |
|||
|
31 Controls |
11.90 ± 0.93 |
OD: 12.87 ± 1.08 D |
||
|
OS: 12.87 ± 1.16 D |
||||
|
Wolfgang Dusek et al. 20105 |
810 poor readers |
9±3 |
OU: 12.54D ± 2.60D |
< 0.001 |
|
308 controls |
9±2.5 |
OU: 13.29D ± 2.05D |
||
|
Azam Darvishi et al. 2022[16 |
32 children with dyslexia |
8.1 ± 0.8 |
Mild dyslexia: OU: 8.2±2.3 |
|
|
Moderate dyslexia: OU: .9.8±2.6 |
0.934 |
|||
|
Severe dyslexia: OU: 8±1.3 |
Discussion
Visual acuity
Studies have suggested that children with dyslexia may have difficulties with visual perception, specifically in terms of visual acuity or clarity of vision, such as problems with visual discrimination, spatial orientation, and visual sequencing. At both a distance of 6 meters and a near distance of 40 centimeters, the visual acuity (VA) of distance was affected in a few studies. However, most studies reported hampered near VA in the dyslexic group. This differesnce in visual acuity is because children with dyslexia tend to have a more difficult time processing visual information. 28, 1, 12, 18
Stereoacuity
The provided information offers a nuanced perspective on the association between dyslexic individuals and normal subjects, emphasizing the role of factors like stereo acuity in various studies. Most studies did not find statistically significant differences in visual characteristics between dyslexic and non-dyslexic participants, suggesting a lack of consistent distinctions. 29, 16.However, a 2019 study12 stands out by reporting a significant difference in stereo acuity for dyslexic individuals, highlighting potential variations in specific visual processing aspects. Acknowledging the importance of considering study limitations, such as sample size and methodology, is crucial. The findings underscore the need for further research to explore the implications of observed differences in stereo acuity on reading abilities and ascertain whether they are primary or secondary factors associated with dyslexia. Collaborative efforts among researchers are vital to reconcile conflicting results and enhance our understanding of the intricate relationship between dyslexia and visual processing, ultimately contributing to the development of effective interventions for individuals with dyslexia.
NPC
The mean distance from the point of convergence was found to be reduced in most of the studies for the “dyslexic” group in comparison with the control groups.10, 3, 20, 21, 22, 5, 19, 26 Similar seen in the convergence insufficient population (p= 0.027).21 The study also found that the NPC break and recovery varied considerably across children in kindergarten, third grade, and sixth grade, suggesting that the age of the dyslexic population should also be taken into account when diagnosis. One of the reasons is associated with underlying neurological and cognitive differences, including problems with visual processing and attention. 20, 30, 31, 28
Fusional vergence testing
Present review of literature has suggested that some children with dyslexia may have fusional vergence difficulties, affecting their ability to read and focus on near objects. Studies found that children with dyslexia had reduced fusional vergence amplitudes compared to typically developing children, indicating a reduced ability to maintain binocular vision while looking at near objects.8, 12, 17, 19 This difficulty in fusional vergence may contribute to visual discomfort and fatigue while reading, exacerbating reading difficulties in children with dyslexia.28 However, it is essential to note that not all children with dyslexia experience problems with fusional vergence and that many other factors can contribute to reading difficulties in these children. Treatment for dyslexia typically focuses on improving language-based skills, such as phonological awareness and decoding, rather than solely targeting fusional vergence. 31
Accommodation accuracy
Accommodative latency of what was found to be optimal represents results within the range of what is considered normal, according to Scheiman and Wick. 32 Children diagnosed with developmental coordination deficit (DCD) had significantly worse accommodative accuracy (without the use of lenses) than children who served as controls.1 According to the outcomes of the binocular facility test, it was discovered that DCD had an accommodation facility of lower quality than controls. Compared to typically developing readers, individuals with developmental dyslexia exhibit significantly lower levels of both monocular and binocular accommodative facility. 19, 1
The amplitude of accommodation was assessed using the push-down method. The Amplitude of Accommodation values were inverted to make sense in the upright position. Results for the push-up were dramatically better than those for the push-down.30 According to statistical analysis, monocular (P = 0.025) and binocularly (P = 0.013), the dyslexic group showed noticeably decreased accommodation amplitude.29, 28 The amplitude of accommodation was reduced in the dyslexic group 17 (p <0.006) binocularly as well as monocularly (p <0.0014) compared to the control group.19 The groups exhibited significant differences in both the amplitude of accommodation (F = 13.67) and monocular accommodative facility (F = 18.11) (P < .001 for both). The dyslexic group exhibited a statistically significant decrease in near point of accommodation (NPA) when assessed monocularly and binocularly. 25, 5
Implications
It is necessary to evaluate the distance and near visual acuity, but a significant effect is seen in the near visual acuity; careful examination for near acuity in dyslexic children is necessary, as it can help to know their difficulty level while performing near tasks. The near point of convergence was noted to be receded in dyslexic children. These differences could affect the ability of the eyes to coordinate when focusing on near objects, leading to problems with near tasks specifically. Consider age concerning the normative value.
Optometric therapies that address fusional vergence may be beneficial for some dyslexic children who feel visual discomfort while reading, as it has been observed that alteration in fusional vergence system in dyslexic children.The affected ability of the eyes to focus on stimuli at varying distances is reported in dyslexic children, which causes ocular discomfort, eyestrain, fatigue, vision impairment, headache, and difficulties in focusing and concerning therapies that can reduce such symptoms. One clinical implication of these findings is that an optometric specialist should examine monocular accommodative amplitude and binocular accommodative capability in children with low reading levels.
Limitations of the Evidences
In addition to the findings of a comprehensive ophthalmologic examination and a full literacy assessment, examinations of vergence, accommodation, and eye movement may be helpful in the first evaluation of children with dyslexia. When assessing people with dyslexia, consider cycloplegia. More study is needed to determine the role of binocular vision on reading comprehension, performance, and fluency. Studying the effects of orthoptic training on reading performance requires combining orthoptic exams with visual instruction and documenting eye movements before and after the intervention.
Conclusion
The present review of literature findings did not provide evidence to support the notion that dyslexic children are more susceptible to any visual condition. However, it is worth noting that some vision abnormalities were more common among persons with dyslexia compared to the control group. While specific vision deficits appeared more common in the dyslexic community than the control population, the findings on dyslexia and vision conflict. However, for children to display their full potential, any visual impairment should be identified as early as possible and suitable accommodations should be made for them. They present a comprehensive assessment of the probable relationships between dyslexia and visual factors, notwithstanding the limitations of the studies that came before them. A list of conditions that have been investigated concerning their impact on dyslexia may be helpful for eye care specialists, educators, and other professionals who work with children with dyslexia. This list can be found in the present review of literature. Thus, the present review is expected to assist eye care professionals in clinical decision making while managing children with dyslexia.
