Causes of Monocular Hemianopia
Monocular hemianopia can occur as a result of damage caused by unilateral retinal or optic nerve diseases, which affect the pre-chiasmal visual pathway.
For instance, a retinal detachment located nasally can lead to a temporal field defect in one eye. Conversely, a temporal retinal detachment can cause a nasal field defect in the affected eye. However, a retinal detachment often results in an atypical hemianopia that extends beyond the midline due to the spatial distribution of retinal photoreceptors.
In addition to retinal detachment, optic nerve compression can also cause monocular nasal or temporal hemianopia. In such cases, there may be a progressive loss of visual field while visual acuity remains preserved. Patients may also experience symptoms such as pain and fluctuating visual loss.
Temporal hemianopia in one eye is frequently associated with optic nerve compression caused by the lateral growth of pituitary gland adenoma (64%) or benign tumors arising from neighboring meningeal structures, known as meningiomas (8%).
Causes of Bi-Temporal or Heteronymous Hemianopia
Bi-temporal hemianopia is commonly caused by a chiasmal lesion that puts pressure on the nasal fibers from each eye. This type of visual field defect is often associated with a compression of the optic chiasm, which can be caused by a pituitary gland tumor developing along the midline. Pituitary gland tumors of this nature tend to grow slowly over time.
A pituitary gland tumor can have an impact on hormone regulation in the body. As a result, along with the visual field defect, individuals may experience symptoms of hormonal imbalance. In some cases, the tumor may impair hormone secretion, leading to a deficiency in one or more hormones produced by the gland. Conversely, the tumor itself may produce excessive hormones, resulting in abnormally high hormone levels and the development of a specific clinical syndrome.