Evidence Based Criteria Diagnosis and Management of Decompensating Heterophoria

Abstract

Introduction: Decompensating exophoria at near is a common condition in optometry practice. The main treatment options for the disorder are relieving prism and Vision Therapy. The prism prescribing techniques are usually derived from two methods: the FD method or the FR method. Neither of these methods is entirely successful. A more recently acknowledged clinical observation in decompensating heterophoria is a reduction in stereopsis. This project aims to investigate the incorporation of global stereopsis testing in prism prescribing for heterophoria. Materials and Methods: A total of 185 participants were recruited. A Stereo Prism Criterion (SPC) was developed: the minimum prism to achieve maximum global stereoacuity on TNO. A relieving prism was prescribed according to Sheard’s Criterion, SPC and FD methods in double-blind crossover studies. 35 participants subsequently underwent VT. The participant’s satisfaction was evaluated using a symptom-based questionnaire. Results: The SPC contributed to a higher prism than Sheard’s and FD (p<0.01) and to greater symptom relief (p<0.01). The TNO is more affected by heterophoria decompensation than local stereo tests. Unlike the other two methods, the SPC prism resulted in a normal level of symptoms (p<0.01). VT using this prism helped reduce signs of decompensation, including symptoms (p<0.01), and improve stereoacuity (p<0.01). Conclusion: The TNO test, known for its sensitivity to decompensating exophoria, has provided a better relieving prism than the commonly used Sheard’s criterion and the FD method. Importantly, the level of symptoms approached that of normal patients without any statistical difference. This suggests that SPC for prescribing prism can be recommended to be used in optometry practice.