The effect of base‐in prism on vision‐related symptoms and clinical characteristics of young adults with convergence insufficiency; a placebo‐controlled randomised clinical trial

Abstract

The aim of the present study was to evaluate the effect of base-in prism on symptoms and clinical characteristics of young adults with convergence insufficiency. In this randomised clinical trial, 64 CI patients aged 18-38years who presented to Bina Eye Hospital, Tehran, Iran between November 2018 and April 2019 were selected and randomly assigned to either prism or placebo groups. All participants underwent complete optometric examinations, including the measurement of visual acuity, objective and subjective refraction, and complete accommodative and binocular vision examinations. Clinical examinations were repeated after three months. The overall score of the Convergence Insufficiency Symptom Survey (CISS) was considered as the primary outcome measure. Secondary outcome measures included near exophoria, positive fusional vergence at near, near point of convergence, vergence facility, monocular accommodative facility, accommodative response, negative relative accommodation and accommodative convergence/accommodation (AC/A) ratio. The mean (S.D.) age of the participants was 25.5 (5.5) years and 44% of them were male. The mean CISS score was significantly lower in the prism group compared to the placebo group in the outcome examination (p<0.001). Moreover, the values of monocular accommodative facility, accommodative response, and negative relative accommodation were significantly higher in the prism group versus the placebo group (p<0.001). There was no significant difference in other parameters, including near positive fusional vergence, near point of convergence, vergence facility, and AC/A ratio between the two groups in the outcome examination (p>0.10). The base-in prism reduced symptoms in young adults with convergence insufficiency, while it had no significant effect on the near point of convergence, near positive fusional vergence, vergence facility and AC/A ratio. However, the results of this study only supports the symptomatic effectiveness of prism in the short term and further studies are needed to assess the long-term effect of prism.