Contralateral Field Defects Research Articles

Contralateral field defect in traumatic globe luxation with optic nerve injury

ABSTRACT Clinical relevance: Traumatic globe luxation is rare vision-threatening event. Besides causing loss of vision in traumatised eye, it may also cause injury to contralateral optic nerve. Any such limitation in a one-eyed patient can make him crippled in his day-to-day activities. Here we hypothesise cause of contralateral field defect in such patients. Background: Traumatic globe luxation is a rare event that leads to profound vision loss due to injury of the ipsilateral optic nerve and rarely a visual field defect in the contralateral eye. Through this communication, we report similar case scenarios and intend to hypothesize the mechanism that results in the occurrence of the contralateral visual field defect. Methods: It is a retrospective, observational study. All cases with traumatic globe luxation were enrolled. Visual field analysis of the contralateral normal eye was main outcome measure. Results: Four patients with traumatic globe luxation and optic nerve injury were studied. There was complete loss of vision in the traumatised eye in all the patients. One patient had complete transection of the optic nerve, whereas in three patients, the course of the optic nerve was intact, on imaging. Three patients had quadrantanopia in the contralateralnormal eye for which oral steroids were given. At 1-month follow-up, there was complete recovery of the visual field defect in two patients. We noticed that all the three patients with an intact course of the ipsilateral optic nerve had quadrantanopia in the contralateral normal eye. Conclusion: We hypothesize that in scenarios where globe luxation is associated with incomplete transection or no transection of the optic nerve, a continuous long standing stretch on the optic nerve, transmits the pulling force to the chiasma which might result in a contralateral field defect as compared to those associated with the complete transection of the optic nerve.

Visual field defects after temporal lobe resection: a prospective quantitative analysis.

To evaluate and quantify prospectively visual field changes in patients undergoing temporal lobe resections for intractable epilepsy. Visual field abnormalities occur after temporal lobe resections for epilepsy; however, we have not encountered published reports using automated static visual field analysis. Humphrey visual fields (program 30-2) were obtained before and after partial temporal lobe resection in 32 consecutive patients with intractable epilepsy. A quantitative point-by-point analysis was made in the affected superior quadrant, and the defects were averaged for the whole patient group. Thirty-one patients developed a visual field defect, but none was aware of the defect. The points nearest fixation were relatively spared. The defects were greatest in the sector closest to the vertical meridian in the eye ipsilateral to the resection. The ipsilateral and contralateral mean field defects also differed in both topography and depth. A significant correlation was found between the extent of lateral temporal lobe resection and the degree of the defect in the contralateral eye. There are differences in the shape and depth of the ipsilateral and the contralateral field defects not previously reported. These findings demonstrate that certain fibers from the ipsilateral eye travel more anteriorly and laterally in Meyer's loop, and support the hypothesis that visual field defects due to anterior retrogeniculate lesions are relatively incongruous because of anatomic differences in the afferent pathways. Automated perimetry is a sensitive method of evaluating and quantifying visual field defects.

Residual vision in the blind field of hemidecorticated humans predicted by a diffusion scatter model and selective spectral absorption of the human eye

The notion of blindsight was recently challenged by evidence that patients with occipital damage and contralateral field defects show residual islands of vision which may be associated with spared neural tissue. However, this possibility could not explain why patients who underwent the resection or disconnection of an entire cerebral hemisphere exhibit some forms of blindsight. We present here a model for the detection of intraocular scatter, which can account for human sensitivity values obtained in the blind field of hemidecorticated patients. The model demonstrates that, under controlled experimental conditions i.e. where the extraocular scatter is eliminated, Lambertian intraocular scatter alone can account for the visual sensitivities reported in these patients. The model also shows that it is possible to obtain a sensitivity in the blind field almost equivalent to that in the good field using the appropriate parameters. Finally, we show with in-vivo spectroreflectometry measurements made in the eyes of our hemidecorticated patients, that the relative drop in middle wavelength sensitivity generally obtained in the blind field of these patients can be explained by selective intraocular spectral absorption.