Identifying Lesion Locations in the Eye
With few exceptions, lesions posterior to the optic chiasm cause visual field loss within the same side of the visual field, or homonymous visual field defects. Complete lesions involving the optic tract, lateral geniculate nuclear, or cortical projections from the lateral geniculate cause complete homonymous hemianopias (HH) which generally do not have additional localizing value, with the exception that optic tract lesions also have associated optic atrophy and a relative afferent pupillary defect.
Incomplete lesions posterior to the optic chiasm cause incomplete HH that may be congruent (symmetric or identical between the 2 eyes) or incongruent (asymmetric or not identical between the 2 eyes). Historically, lesions that caused incongruent homonymous defects were thought to be more anteriorly located (towards the optic tract) and those that caused congruent defects were thought to be more posterior (towards the occipital lobes).
Kedar S, Zhang X, Lynn MJ, Newman NJ, Biousse V
Am J Ophthalmol. 2007;143:772-780
Kedar S, Zhang X, Lynn MJ, Newman NJ, Biousse V
Am J Ophthalmol. 2007;143:772-780
The authors of this retrospective observational study reviewed the records of 530 patients with 548 incomplete homonymous hemianopic defects seen over a 15-year period. Of these defects, 373 were congruent and 175 incongruent. Cerebrovascular disease accounted for 75% of the congruent defects and 55.8% of the incongruent defects. Trauma and intracranial tumors accounted for 20.5% congruent HH and 34.5% of incongruent HH. Lesion locations for congruent HH vs incongruent HH included: occipital lobe 47.9% vs 21.3%, occipital lobe and optic radiations in 8.3% vs 5.6%, optic radiations in 32.4% vs 50.6%, optic tract in 7.2% vs 16.3%, and other locations in 4.2% vs 6.3%. More congruent HH were caused by more posterior lesions in the visual pathway; however, 50% of optic tract lesions and 59% of optic radiation lesions caused congruent HH.
The findings of this study suggest that while lesions of the more posterior visual pathways (occipital lobe) tend to cause congruent HH, at least 50% of lesions in other locations may also cause congruent HH. The authors of this study suggested that the prior rules of congruency be applied with caution. This study contains the largest series of patients with HH and a lesion site confirmed by neuroimaging.
While anatomic localization of lesions causing HH may be academically interesting, from the clinical standpoint it is worth asking whether there is importance when the detection of any type of HH suggests the need for neuroimaging. In many cases, precise localization may not be important. However, in some patients the lesions may be small and otherwise overlooked if the area within the visual pathway is not targeted correctly.
In the accompanying editorial, the author noted that an increasing volumetric proportion of brain tissue is devoted to vision in more posterior regions of the visual pathway, and therefore lesions in these areas may damage focal areas, making congruency more likely to be detected. In addition, kinetic perimetry may misclassify defects depending on the number of isopters used. Despite these potential shortcomings, the findings of this study challenge prior preconceptions which have been held for the past century.
Abstract
Introduction
With few exceptions, lesions posterior to the optic chiasm cause visual field loss within the same side of the visual field, or homonymous visual field defects. Complete lesions involving the optic tract, lateral geniculate nuclear, or cortical projections from the lateral geniculate cause complete homonymous hemianopias (HH) which generally do not have additional localizing value, with the exception that optic tract lesions also have associated optic atrophy and a relative afferent pupillary defect.
Incomplete lesions posterior to the optic chiasm cause incomplete HH that may be congruent (symmetric or identical between the 2 eyes) or incongruent (asymmetric or not identical between the 2 eyes). Historically, lesions that caused incongruent homonymous defects were thought to be more anteriorly located (towards the optic tract) and those that caused congruent defects were thought to be more posterior (towards the occipital lobes).
Kedar S, Zhang X, Lynn MJ, Newman NJ, Biousse V
Am J Ophthalmol. 2007;143:772-780
Congruency in Homonymous Hemianopia
Kedar S, Zhang X, Lynn MJ, Newman NJ, Biousse V
Am J Ophthalmol. 2007;143:772-780
Summary
The authors of this retrospective observational study reviewed the records of 530 patients with 548 incomplete homonymous hemianopic defects seen over a 15-year period. Of these defects, 373 were congruent and 175 incongruent. Cerebrovascular disease accounted for 75% of the congruent defects and 55.8% of the incongruent defects. Trauma and intracranial tumors accounted for 20.5% congruent HH and 34.5% of incongruent HH. Lesion locations for congruent HH vs incongruent HH included: occipital lobe 47.9% vs 21.3%, occipital lobe and optic radiations in 8.3% vs 5.6%, optic radiations in 32.4% vs 50.6%, optic tract in 7.2% vs 16.3%, and other locations in 4.2% vs 6.3%. More congruent HH were caused by more posterior lesions in the visual pathway; however, 50% of optic tract lesions and 59% of optic radiation lesions caused congruent HH.
Comment
The findings of this study suggest that while lesions of the more posterior visual pathways (occipital lobe) tend to cause congruent HH, at least 50% of lesions in other locations may also cause congruent HH. The authors of this study suggested that the prior rules of congruency be applied with caution. This study contains the largest series of patients with HH and a lesion site confirmed by neuroimaging.
While anatomic localization of lesions causing HH may be academically interesting, from the clinical standpoint it is worth asking whether there is importance when the detection of any type of HH suggests the need for neuroimaging. In many cases, precise localization may not be important. However, in some patients the lesions may be small and otherwise overlooked if the area within the visual pathway is not targeted correctly.
In the accompanying editorial, the author noted that an increasing volumetric proportion of brain tissue is devoted to vision in more posterior regions of the visual pathway, and therefore lesions in these areas may damage focal areas, making congruency more likely to be detected. In addition, kinetic perimetry may misclassify defects depending on the number of isopters used. Despite these potential shortcomings, the findings of this study challenge prior preconceptions which have been held for the past century.
Abstract
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