If the patient develops a hypertropia, the nasal hemifields will separate vertically. If patients develop an exotropia, the nasal hemifields will overlap slightly, resulting in superimposition of images. In the hemifield slide phenomenon, patients with pre-existing esophoria or intermittent esotropia may have hemifields that drift apart horizontally, with the right nasal hemifield drifting further to the left and the left nasal hemifield drifting further to the right. Loss of input from this central zone results in difficulty maintaining the two half fields juxtaposed. It has been previously noted that a vertical median strip of the retina exists contains retinal ganglion cells that project to both optic tracts, allowing the visual fields to overlap and appear uniform with no interruption of midline. Normally, the nasal field of one eye overlaps with the temporal field of the contralateral eye to permit stable binocular fusion. ![]() The hemifield slide phenomenon occurs in patients with limited temporal visual fields, when pre-existing phorias develop into tropias. It is important to recognize these phenomena to avoid unnecessary and potentially harmful strabismus surgery. ![]() In all of these etiologies, there is impairment of the normal fusional process. Etiologies include hemifield slide phenomenon, dragged-fovea diplopia syndrome, supranuclear fusional abnormalities, image disparity, and horror fusionis, which we will discuss in detail below. Non-paretic binocular diplopia refers to diplopia that is not a result of dysfunction of any muscle. 1.2.4 Etiologies causing image disparityĪ summary video by Dr Andrew Lee can be accessed here: Disease. ![]() 1.2.3 Supranuclear fusional abnormalities.1.2.2 Dragged-fovea diplopia syndrome (DFDS).
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