The use of prisms and botulinum toxin in the detection of binocular vision: a literature review

Aim: The aim of this literature review is to compare orthoptic prisms and botulinum toxin in the diagnostic testing of strabismus patients. A direct comparison will be carried out between both methods used for predicting post-operative diplopia and binocular single vision (BSV). A further comparison of the complications and cost effectiveness of both methods will be conducted.

Methods: A review of the literature was conducted using journals available at the University of Liverpool, along with the scholarly online resources PubMed, Web of Science and Google Scholar and the orthoptic search facility (http://pcwww.liv.ac.uk/~rowef/index_files/Page646.htm). Search terms included ‘post-operative diplopia’, ‘binocular single vision’, ‘prisms’ and ‘botulinum toxin’.

Results: Botulinum toxin provides accurate positive and negative predictive responses for post-operative diplopia testing and is useful in assessing BSV potential in strabismus patients. Prisms can correctly identify patients with no risk of post-operative diplopia, but have a poor predictive outcome for diagnosing those at risk. The use of prisms to assess BSV potential in patients has not been well established in the literature.

Conclusion: Botulinum toxin appears to be more effective overall in detecting a binocular response; however, the complications and individual needs of the patient must be considered before testing. The accuracy of prisms in detecting patients who will not get post-operative diplopia, and the reduction in cost compared to botulinum, would indicate that they should be used in the first instance. If the patient detects double vision on prism testing, then an injection of botulinum toxin is indicated to determine an accurate result. Further research on the use of prisms to diagnose BSV potential compared to botulinum toxin is required in order to conclude which method is most effective in this area.