Hemifield Slide Phenomenon- the Double Trouble

Binocular diplopia results from a breakdown in the fusional capacity of the binocular system. Among the several potential mechanisms of binocular diplopia, hemifield slide phenomenon remains a rare and under- recognized entity. It is a sensory phenomenon, causing diplopia without paresis of the cranial nerves. The earliest description of this phenomenon was as “non-paretic diplopia” in patients with underlying pituitary adenomas [1,2]. Although typically described with bitemporal hemianopia, it can occur with any heteronymous hemianopic defects like binasal hemianopia or altitudinal field defect [3,4].

Physiologically, nasal and temporal visual fields overlap between the right and left eyes. The area of overlap between the visual fields of both eyes allows the corresponding retinal points to be established. The corresponding points have a common visual direction and thus permits fusion and single vision. Ocular manifestations depend on the type of visual field defect as well as the accompanying tropias [5]. In bitemporal hemianopia, each eye has a loss of its temporal field of vision, which results in the absence of overlap of the visual fields between the two eyes. As a result, the corresponding retinal points can’t be established which disrupts the normal fusion. This lack of fusion decompensates any pre-existing phoria into a tropia. In orthotropia, with binocular vision, the impaired temporal visual field of each eye is partially compensated for by the contralateral eye’s intact nasal visual field (Figure 1A). Hence the image of an object at the point of fixation is seen as single.

Figure 1:Mechanism of hemifield slide phenomenon.
a) Bitemporal Hemianopia.
b) Bitemporal Hemianopia and Exotropia.
c) Bitemporal Hemianopia and Esotropia.
d) Bitemporal Hemianopia and Hypertropia.

In vertical deviations, the eyes deviate upwards or downwards, causing the visual hemifields to slide vertically respective to one other (Figure 1D). For example, in hypertropia, the eyes deviate upwards. Left half of the object is displaced downwards compared to the right half of the object resulting in split diplopia.

Currently no specific treatment guidelines exist for management of hemifield slide phenomenon. In cases of respectable intracranial tumor like a pituitary macroadenoma, surgical resection is the choice when medical management has failed or is not applicable [6]. Prisms may decrease symptoms in partial bitemporal hemianopia where there is sufficient area of retinal correspondence. Fusional convergence exercises can aid in fusion of visual fields in cases of horizontal deviations [7]. Stereo-typoscope (Figure 2) is a simple reading aid developed recently to alleviate the disturbing diplopia for near [8]. It works on the principle that midline stereopsis operates without corresponding retinal points. In bitemporal hemianopia, posterior midline falls in post fixational scotoma. Stereo-typoscope provides an anterior midline stereoscopic stimulus which trigger fusional eye movements. It is made of cardboard of some thickness to provide depth/disparity. Surface has high contrast vertical stripes that provide strong stimuli for disparity and stereopsis in near periphery.

Figure 2:Stereo-typoscope.

It is recommended that all patients with hemifield slide phenomenon gets a detailed visual field testing and orthoptic evaluation to identify areas of binocular fusion. In addition, Simple modalities like fusional vergence exercises and stereo-typoscope can bring relief to the distressing symptoms produced by hemifield slide phenomenon.

1. Kirkham TH (1972) The ocular symptomatology of pituitary tumours. Proc R Soc Med 65(6): 517-608.
2. Bardram MT (1949) Oculomotor pareses and non-paretic diplopia in pituitary adenomata. Acta Ophthalmol 27(2): 225-258.
3. Peragallo JH, Bialer OY, Pineles SL, Newman NJ (2014) Hemifield slide phenomenon as a result of heteronymous hemianopia. Neuro ophthalmology 38(2).
4. Borchert MS, Lessell S, Hoyt WF (1996) Hemifield slide diplopia from altitudinal visual field defects. J Neuroophthalmol 16(2): 107-109.
5. Waveren, MV, Jägle H, Besch D (2013) Management of strabismus with hemianopic visual field defects. Graefes Arch Clin Exp Ophthalmol 251(2): 575-584.
6. Mota M, Silvaet F, Pina S, Silva D, Colaço L, et al. (2017) Hemifield slide phenomenon from pituitary macroadenoma. The Pan-American Journal of Ophthalmology 16(4): 121-123.
7. Ko TC, Wu P KW, Lo BKK (1999) Hemifield slide phenomenon in a patient with bitemporal hemianopia. HKJ Ophthalmol 3(1): 48-50.
8. Peli, E, Satgunam PN (2014) Bitemporal hemianopia; its unique binocular complexities and a novel remedy. Ophthalmic Physiol Opt 34(2): 233-242.