Quadrantanopia, quadrantanopsia, or quadrant anopia refers to an anopia affecting a quarter of the field of vision.

It can be associated with a lesion of an optic radiation. While quadrantanopia can be caused by lesions in the temporal and parietal lobes, it is most commonly associated with lesions in the occipital lobe.

Individuals with quadrantanopia often modify their behavior to compensate for the disorder, such as tilting of the head to bring the affected visual field into view. Drivers with quadrantanopia, who were rated as safe to drive, drive slower, utilize more shoulder movements and, generally, corner and accelerate less drastically than typical individuals or individuals with quadrantanopia who were rated as unsafe to drive. The amount of compensatory movements and the frequency with which they are employed is believed to be dependent on the cognitive demands of the task; when the task is so difficult that the subject's spatial memory is no longer sufficient to keep track of everything, patients are more likely to employ compensatory behavior of biasing their gaze to the afflicted side. Teaching individuals with quadrantanopia compensatory behaviors could potentially be used to help train patients to re-learn to drive safely.

Hemianopsia, or hemianopia, is a decreased vision or blindness (anopsia) in half the visual field, usually on one side of the vertical midline. The most common causes of this damage are stroke, brain tumor, and trauma.

This article deals only with permanent hemianopsia, and not with transitory or temporary hemianopsia, as identified by William Wollaston PRS in 1824. Temporary hemianopsia can occur in the aura phase of migraine.

An anopsia or anopia is a defect in the visual field. If the defect is only partial, then the portion of the field with the defect can be used to isolate the underlying cause.

Types of partial anopsia:

- Hemianopsia

- Homonymous hemianopsia

- Heteronymous hemianopsia

- Binasal hemianopsia

- Bitemporal hemianopsia

- Superior hemianopia

- Inferior hemianopia

- Quadrantanopia

The term "anopsia" comes from the Ancient Greek ἀν- ("an-"), "un-" and ὄψις ("opsis") "sight".

When the pathology involves both eyes, it is either homonymous or Heteronymous.

Phonological dyslexia is a reading disability that is a form of alexia (acquired dyslexia), resulting from brain injury, stroke, or progressive illness and that affects previously acquired reading abilities. The major distinguishing symptom of acquired phonological dyslexia is that a selective impairment of the ability to read pronounceable non-words occurs although the ability to read familiar words is not affected. It has also been found that the ability to read non-words can be improved if the non-words belong to a family of pseudohomophones.

Several studies have found that different levels of brain damage can lead to the occurrence of varying forms of non-word reading disorders. It has been found that during certain tasks, dyslexics had activated one of two regions of the brain: the Broca's area, which is responsible for speech, or the Wernicke's area, which is responsible for forming and understanding. Both areas were seldom active together. This study has led to the conclusion that there exist neural connection breakdowns between the language centers that may be causing dyslexia.

Although the causes of craniopharyngioma is unknown, it can occur in both children and adults, with a peak in incidence at 9 to 14 years of age. There are approximately 120 cases diagnosed each year in the United States in patients under the age of 19 years old. In fact, more than 50% of all patients with craniopharyngioma are under the age of 18 years. There is no clear association of the tumor with a particular gender or race. It is not really known what causes craniopharyngiomas, but they do not appear to "run in families" or to be directly inherited from the parents.

Craniopharyngioma is a type of brain tumor derived from pituitary gland embryonic tissue, that occurs most commonly in children but also in adults in their 50s and 60s. People may present with bitemporal inferior quadrantanopia leading to bitemporal hemianopsia, as the tumor may compress the optic chiasm. It has a point prevalence of approximately 2/100,000. Craniopharyngiomas are also known as Rathke pouch tumors, hypophyseal duct tumors, or adamantinomas.

Carcinomas that metastasize into the pituitary gland are uncommon and typically seen in the elderly, with lung and breast cancers being the most prevalent, In breast cancer patients, metastases to the pituitary gland occur in approximately 6-8% of cases.

Symptomatic pituitary metastases account for only 7% of reported cases. In those who are symptomatic Diabetes insipidus often occurs with rates approximately 29-71%. Other commonly reported symptoms include anterior pituitary dysfunction, visual field defects, headache/pain, and ophthalmoplegia.

Adenomas of the anterior pituitary gland are a major clinical feature of multiple endocrine neoplasia type 1 (MEN1), a rare inherited endocrine syndrome that affects 1 person in every 30,000. MEN causes various combinations of benign or malignant tumors in various glands in the endocrine system or may cause the glands to become enlarged without forming tumors. It often affects the parathyroid glands, pancreatic islet cells, and anterior lobe of the pituitary gland. MEN1 may also cause non-endocrine tumors such as facial angiofibromas, collagenomas, lipomas, meningiomas, ependymomas, and leiomyomas. Approximately 25 percent of patients with MEN1 develop pituitary adenomas.