An Evaluation of Clinical Treatment of Convergence Insufficiency For Children With Reading Difficulties

Wolfgang A Dusek; Barbara K Pierscionek; Julie F McClelland


BMC Ophthalmol. 2011;11(21) 

In This Article


Reading and writing are the most important learning performance indicators in the early school years. Whilst it is now recognised that an apparently underachieving child may not lack intellectual prowess or ability but that there may be functional or psychological issues that impede learning, there is still a paucity of basic investigations to determine how some of these problems can be addressed or alleviated. A diagnosis of a specific reading difficulty is a significant concern for parents and children and it is possible that basic binocular visual problems are overlooked amidst the investigations. Even when visual problems are diagnosed, if these are vergence-based, prismatic correction is not routinely prescribed. Too few studies have compared the effect of a relatively high prismatic correction with other treatment modalities on children with visual problems such as CI which affects reading performance.

All measurements in this study were obtained using the same techniques under uniform, controlled conditions and conducted by the same practitioner ensuring the avoidance of practitioner variability.

Improvements in five outcome measures (reading speed, reading error score, amplitude of accommodation, vergence facility, and binocular accommodative facility) were noted between results obtained for visits 1 and 2. In addition, significant differences between treatment groups were observed for reading speed and reading error score, with subjects with the prism spectacles showing the greatest improvements. Whilst statistical significance may not always manifest as significant in the clinical realm as the changes may be too subtle, this study indicates which visual functions were affected by the various treatment options and, most importantly from the perspective of the scholastic attainment, which showed improvements in reading. Reading speed is an important outcome measure as it reflects clinically significant changes in results in addition to statistically significant results. Changes in reading speed provide data that is meaningful and highly applicable to daily living tasks.

Scheiman et al.[18] suggest that base-in reading spectacles are not an appropriate treatment option for CI as they were no more effective than placebo spectacles at improving near point of convergence, fusional vergence or reducing asthenopic symptoms. However, the present study found that prism spectacles with 8Δ base-in significantly improved both reading speed and reading errors scores. Most importantly, this was the only treatment that improved both total reading time and error score which is most pertinent to scholastic achievement. The discrepancy in findings between this study and previous work[18] may be explained by the differences in the study populations, differences in the prescribed spectacles or type of outcome measures used. In the present study subjects were between 7 and 14 years of age. The previous study was conducted on a group ranging in age from 9 to 18 years. It may be possible that the slightly younger cohort in this study was more amenable to treatment as they had not yet reached the end of the sensitive period for visual development. Differences may also be attributed to the size of the prism used for treatment. Scheiman et al[18] based the size of the prism prescribed on Sheard's criterion and this resulted in a mean value of 4.14Δ. It is possible that the larger amount of prism prescribed in the present study allowed comfortable clear single vision to be obtained for longer periods. It is interesting to note that these improvements in reading speed and reduction in reading error scores were obtained in the absence of the base-in spectacles. This may be due to the spectacles stimulating an improvement in fusional reserves demonstrated by the improvements in vergence facility tests. It is unlikely that that the improvements noted in reading ability were due to a learning effect as these tests were performed on only two occasions and the tests included both real and pseudo words.

It may be argued that the length of time between visits was relatively short in comparison to other studies.[18] The four week period was chosen to ensure that the subjects were monitored carefully, that the treatment did not have a detrimental effect on visual function and that subjects did not tire of the treatment and cease its application. In addition, the authors were aware that the reading ability and speed of school children may increase significantly over a longer time period purely due to educational development over time. Due to the short time period used, any improvements in visual function are more likely to be attributable to the CI treatment rather than to a general improvement in reading skills. The four week period between visits allowed sufficient time for adaptation to the new spectacles.

Questionnaires developed for use in children with CI have been reported.[30,31] Scheiman et al.[18] demonstrated no improvement in the Convergence Insufficiency Symptom Survey score with the use of base-in prism reading glasses in a group of children aged 9–18 years. The use of questionnaires in the present study would have been of limited value due to the younger cohort in the present study compared to that of Scheiman et al.[18] and the subjective nature of the outcome measure: symptoms and their reporting can be vague and unreliable particularly with younger subjects.

In accordance with previous studies the HTS produced an improvement in various measures of visual function (including reading error score, amplitude of accommodation, binocular accommodative facility and vergence facility).[14,16,20] Although patient compliance may pose a concern with this form of treatment, this was monitored by parents and the practitioner throughout the present study using data generated by the HTS. Results of the present study suggest that the use of the HTS provides a useful alternative to base-in prism spectacles where the optical correction is not acceptable to patients. Some computer based vision therapy systems may prove difficult and confusing for children, especially those of younger age, and the relatively time consuming nature of the treatment may cause children and parents to give up easily and not to persist with treatment if improvements in visual function are not immediately noticeable. It is postulated that compliance with spectacle treatment of CI with base-in prism reading spectacles was good as the treatment provides immediate relief for children struggling with near vision tasks. However, it was only possible to assess this based on parent's and subject's opinions.

All measurements were obtained by the same examiner (WD) to avoid practitioner variations. The examiner did not enquire about what treatment had been given, when the subject returned for the second visit. Whilst it cannot be ruled out that the examiner may have been aware in some cases to which treatment group individual subjects belonged, the major outcome variables: reading speed and accuracy, were measured with a test that is as objective as possible, minimising the influence of any bias. The latter point notwithstanding, where the experiment is not conducted as a randomised clinical trial, bias cannot be ruled out. Potential sources of bias in this investigation are most likely to be related to the reasons why a given treatment option was chosen. Such preferences could be affected by certain functional factors (e.g. refractive status, vergence capacity), visual demands (e.g. time spent doing near work) or they may stem from inherent psychological characteristics that may influence the choice of a particular treatment option (e.g. a preference for or aversion to the wearing of spectacles). Whilst, it is not possible to investigate all these potential sources of bias in the present study, functional factors that could be determined clinically were measured and it was assumed that the demands on the visual system did not vary significantly from one treatment group to another. However, subtle functional differences that may not be manifest clinically and that may influence choice cannot be dismissed and may form the basis of further investigations in this area. Likewise, questionnaire based studies that probe time spent on near activities and on the types of activities may reveal further sources of bias. It is difficult to speculate on potential psychological reasons for choice of treatment as these are beyond the scope of this study, whilst the subjects were assessed by an educational psychologist and no data relating to psychological testing was accessible. This clinical study provides useful and seminal preliminary data that warrant further investigation, that ideally should be followed up in a randomised controlled trial.

Treatment of CI in children with reading difficulties is important to prevent these visual anomalies from further compounding educational issues associated with the reading difficulties. Reading difficulties associated with binocular vision anomalies are highly likely to lead to reduced educational attainment.[1] This may prevent a child from progressing through school with their peer group and would cause unnecessary social exclusion.