CONVERGENCE INSUFFICIENCY AND COGNITIVE IMPAIRMENT IN PARKINSONIAN DISORDERS

Abstract

Convergence insufficiency, an inability to coordinate binocular eye movements to maintain single vision during near target viewing, is increasingly recognized as a cause of disabling visual dysfunction for near tasks (i.e. reading) in parkinsonian conditions, and is most often reported by patients as double vision. While cognitive complaints may be more common in patients with Parkinson's disease who report diplopia,1 the relationship between cognitive impairment, subjective visual symptoms, and objectively measured convergence insufficiency has not previously been investigated. Twenty-four participants with parkinsonian disorders (21 Parkinson's disease, 4 progressive supranuclear palsy) referred for neuro-ophthalmologic evaluation with objective findings of convergence insufficiency (near point of convergence of ≥ 10 cm or a near/distance exotropia disparity of ≥ 10 prism diopters), with visual acuity better than 20/40 best corrected, were included in this analysis. Subjective reports of visual symptoms of convergence insufficiency (i.e. near task symptoms of blurred or double vision or eye strain) were recorded. Participants completed the Self-Administered Gerocognitive Examination (SAGE) as a global cognitive screening measure; subjective cognitive complaints were also recorded. Seventy-five percent of all participants reported subjective cognitive complaints, and 41.7% met SAGE criteria for cognitive impairment (total score<17). Seventy-five percent of participants reported subjective visual symptoms that could be attributed to convergence insufficiency. There were no significant differences in demographic variables, measured near point of convergence, or cognitive outcomes between the symptomatic and non-symptomatic convergence insufficiency groups [Table 1]. While there was no significant difference in cognitive scores between participants who reported visual symptoms and those who did not, there was a high rate of cognitive impairment in parkinsonian disorders presenting with objective convergence insufficiency. Beyond the midbrain, cortical control of convergence has been postulated to be controlled reflexively by posterior parietal regions and volitionally by frontal regions. Further investigation into the onset of convergence insufficiency in relationship to cognitive impairment in parkinsonian disorders is warranted, as convergence insufficiency could serve as an additional clinical marker of cognitive impairment in these conditions. Reference: Schindlbeck KA, et al. Characterization of diplopia in non-demented patients with Parkinson's disease. Parkinsonism Relat Disord. 2017 Dec;45:1-6.