superior altitudinal visual field defect causes
-superior altitudinal visual field defect causes
It can quickly establish the pattern of visual field loss in the ill, poorly attentive, or elderly patient who requires continued encouragement to maintain fixation and respond appropriately. 2) Superior / inferior arcuate defect The most common early to mid stage glaucomatous field. [5], Characteristically lesions at the level of the optic chiasm produce a bitemporal hemianopia. In an optic tract lesion, there may be a relative afferent pupillary defect (typically in the eye with greater visual field loss), or a special type of optic atrophy called band or bow-tie optic atrophy representing nasal fiber loss in the eye with the temporal visual field defect. A follow-up of 52 patients. We report a patient with bilateral superior altitudinal hemianopia. 1. Nasal retina of the right eye ([2red]) in Fig. Surgical debulking of pituitary tumors is often performed by otorhinolaryngology (ENT) or neurosurgery.[35]. 10. Thus the nasal visual field extends to 60% of the horizon, whereas the temporal field extends to a further 30-40. The lower visual field falls on the superior retina (above the fovea). Current methods of visual field testing all require the subject to indicate whether the stimulus is seen or not. "Tumors of the Pituitary Gland." Octreotide has the most effect on tumor shrinkage, and pegvisomant has no effect on tumor size or growth hormone secretion but may have better effect on the overall systemic effects of elevated growth hormone. 3.22d). (one eye with horizontal blindness) . The nasal visual field extends to 60% of the horizon, whereas the temporal field. A right homonymous hemianopia (contralateral to lesion) The laboratory tests may vary depending on the clinical presentation. Guaraldi F, Salvatori R. Cushing syndrome: maybe not so uncommon of an endocrine disease. Fig. Multiple Endocrine Neoplasia Type 1 (MEN1) Syndrome. Hemifield slide diplopia from altitudinal visual field defects. Please send feedback, questions, and corrections to tcooper@stanford.edu. Case presentation A 48-year-old man complained of visual disturbance on wakening following radiofrequency catheter ablation. Visual fields should be tested monocularly given that the overlap in binocular fields may mask visual field defects. 1. A left optic tract syndrome includes the following: Bowtie atrophy of the right optic nerve, Mostly temporal pallor of the left optic nerve. 4. The link you have selected will take you to a third-party website. It causes sudden, painless, unilateral, and usually severe vision loss. What is the visual field defect of a junctional scotoma? What are the findings of an occlusion of the posterior cerebral artery? 9. [6], Silent-subtype III is a plurihormonal pituitary adenoma that derives from the Pit-1 lineage and expresses one or more hormones in scattered foci. [28] Patients may experience overlapping images or divergent images corresponding to esodeviation, exodeviation, or hyperdeviation. The normal extent of field of vision is 50 superiorly, 60 nasally, 70 inferiorly and 90 temporally. [6], Pituitary "incidentalomas" are lesions of any kind found in the pituitary on imaging performed for a different purpose. 3. These tumors also have a poor reticulin network, which distinguishes the tumor from non-neoplastic tissue, which tends to have a heterogenous appearance with an extensive reticulin network.[3]. Incomplete homonymous hemianopias may help localize the lesion based on their congruity: Seesaw nystagmus caused by giant pituitary adenoma: case report. 3.8). Kumar V, Ramanathan US, Mushtaq B, Shah P (2002) Artefactual uniocular altitudinal visual field defect. Adapted from Bagheri N, Duraani AK: The Wills Eye Manual, ed. Lactotroph adenomas arise from Pit-1 lineage and mainly express prolactin (PRL) and estrogen receptor (ER). Currently, there is no effective treatment to reverse the visual impairment in NAION. Symptoms include night blindness and loss read more or another peripheral retinal disorder, chronic papilledema, following panretinal photocoagulation, central retinal artery occlusion Central Retinal Artery Occlusion and Branch Retinal Artery Occlusion Central retinal artery occlusion occurs when the central retinal artery becomes blocked, usually due to an embolus. Does the visual field defect involve one eye or two eyes? 3.22d) 3.10 labeled Pattern Deviation highlights focal abnormalities in the visual field, helping to emphasize the pattern of visual field loss. This superior wedge shaped area of vision loss is called a "pie in the sky.". For example, the pituitary tumor-transforming gene (PTTG) has been shown to be overexpressed in hormone-secreting adenomas. This symptom was first overlooked and a delusion was suspected. What are the monocular VF defect patterns? Stacy Smith, Andrew Lee, Paul Brazis. A lesion in this area will give rise to monocular visual field defect affecting the contralateral eye. be sent after the lecture with information on many defects; Retina - Causes ##### Lesions at the level of the retina cause ##### monocular visual field defects ##### Retinal Detachment . The tangent screen is rarely used and is primarily helpful for evaluating patients suspected of nonorganic constriction of the visual field (Fig. [3] One review found an average incidence of 16.7% (14.4% in autopsy studies and 22.5% in radiologic studies). Junctional scotoma, Bitemporal defects, Homonymous hemianopia defects (w/wo macular sparing, spared temporal crescent). 3. 3.3.2 Assessing the Quality of the Visual Field. [26] Patients with chiasmal disease will experience Pulfrich phenomenon physiologically. The underlying diagnosis is often serious and can threaten long-term vision and even the patients well-being. - hypothyroidism . [6], Most pituitary adenomas are soft, well-circumscribed lesions that are confined to the sella turcica. Where is the lesion of a junctional scotoma? Patients can have decreased consciousness or strokes from extravasation of blood into the subarachnoid space. 3.15, Fig. Ask the patient to signal detection of the white dot by pressing a buzzer. Rates must be under: Ischemic Optic Neuropathy Ischemic optic neuropathy is infarction of the optic disk. [7][8] While most pituitary adenomas occur in isolation, 3% of cases are associated with multiple endocrine neoplasia (MEN) type 1.[3][9]. What is the visual field defect of a junctional scotoma? Visual field defects seen in each eye's visual field and the image perceived by the patient: a) right HH; b) left HH; c) left HH with macular sparing; d) right superior quadrantanopia, 'pie in the sky'; e) inferior quadrantanopia 'pie on the floor' Figure 2. [21], Cushing syndrome can result from both exogenous and/or endogenous sources, which makes the diagnostic workup of a patient presenting with Cushing syndrome very challenging. 3. Lateral Geniculate Nucleus 1. 1. What field defects results from ischemia limited to of the tip of an occipital lobe? The lesion is at the most posterior portion of the optic nerve ipsilateral to the central scotoma at its junction with the chiasm. What are the findings of bilateral occipital lobe lesions? The most common cause is a retinal break (a tear or, less commonly, a hole) (rhegmatogenous read more, Less common: Glaucoma Overview of Glaucoma Glaucomas are a group of eye disorders characterized by progressive optic nerve damage in which an important part is a relative increase in intraocular pressure (IOP) that can lead to irreversible read more , optic nerve lesion, optic nerve coloboma, A small, bow-shaped (arcuate) visual field defect that follows the arcuate pattern of the retinal nerve fibers; does not cross the horizontal median, Damage to ganglion cells that feed into a particular part of the optic nerve head, More common: Glaucoma Overview of Glaucoma Glaucomas are a group of eye disorders characterized by progressive optic nerve damage in which an important part is a relative increase in intraocular pressure (IOP) that can lead to irreversible read more, Less common: Ischemic optic neuropathy Ischemic Optic Neuropathy Ischemic optic neuropathy is infarction of the optic disk. 3.2.1 Visual Field Testing at Bedside Less commonly, ophthalmologists may be the first to detect evidence of a pituitary adenoma. Goldmann perimetry has the advantage of charting the entire visual field and includes the far temporal periphery (Fig. Treatment for the nonarteritic read more or Leber hereditary neuropathy Leber hereditary optic neuropathy Hereditary optic neuropathies result from genetic defects that cause vision loss and occasionally cardiac or neurologic abnormalities. Fig. It can be arteritic or nonarteritic. Various studies report that pituitary adenomas account for anywhere from 66% to 80% of endogenous Cushing syndrome cases. Retro-chiasmal lesions normally cause homonymous visual field defects; the only exception is the temporal crescent or half moon syndrome, caused by a lesion in the anterior part of the contralateral parieto-occipital sulcus. Heteronymous Altitudinal Visual Field Defect and Deviations. 13. It can be repeated to monitor if the defects are growing or shrinking as a measure of whether the disease process is worsening or improving. Does the visual field defect involve one eye or two eyes? It can be repeated to monitor if the defects are growing or shrinking as a measure of whether the disease process is worsening or improving. [49] It was found that recurrence rates can be decreased with a combination treatment of surgery and radiotherapy (from 7-35% to 7-13%). Wilbrands knee is composed of fibers originating in the inferonasal retina which after traversing via the optic nerve and crossing in the chiasm go anteriorly into the contralateral optic nerve up to 4 mm before passing posteriorly to the optic tract. (B) Automated perimetry in the right eye is normal; left eye shows an inferior altitudinal defect. Right RAPD 6. Retrochiasmal lesions normally cause homonymous visual field defects; the only exception is the temporal crescent or half moon syndrome, caused by a lesion in the anterior part of the contralateral parieto-occipital sulcus. Nonsolid tumors (macrocystic and macrohemorrhagic) have been suggested to be more effectively managed with transsphenoidal hypophysectomy in comparison with solid tumors.[34]. [39] Endoscopic techniques have improved visualization of the tumor and allowed for smaller incisions and faster healing. Retina Ask the patient to count fingers in two quadrants simultaneously. Where is the lesion of a junctional scotoma? 3. Because the nerve fiber layer arising from the peripheral retina arches over the fovea, superior or inferior nerve fiber layer damage results in arcuate-shaped visual field defects. Upper Altitudinal Hemianopia is caused as a result of destruction of bilateral destruction of lingual gyri. In optometry, ophthalmology, and neurology, a visual . double vision. Macular lesions produce central or paracentral defects, whereas most degenerative retinopathies, such as retinitis pigmentosa, produce progressive constriction of the peripheral and midperipheral visual field (Fig. 11. Depending on the etiology of the optic neuropathy, arcuate defects, altitudinal defects, and central, paracentral, or centrocecal scotomas are observed (Fig. Visual fields should be tested monocularly given that the overlap in binocular fields may mask visual field defects. Questions with answers: Lesions of the optic tract (left optic tract lesion in the example in Fig. 2. PubMedGoogle Scholar. The ocular symptomatology of pituitary tumours. Is the test normal or not? 3. A consistent difference in color perception (use a red object) across the horizontal or vertical meridian may be the only sign of an altitudinal or hemianopic defect, respectively. The diagnosis is confirmed by CT or MRI. Malenkovi V, Gvozdenovi L, Milakovi B, Sabljak V, Ladjevi N, Zivaljevi V. Preoperative preparation of patients with pituitary gland disorders. Expansion may lead to bony erosion of the anterior clinoid processes and sella turcica, as well as extending into the cavernous and sphenoid sinuses. A 46-year-old woman with a monocular superior altitudinal visual defect due to an aneurysm in the supraclinoid portion of the internal carotid artery appeared to have compressed the optic nerve and secondarily caused posterior ischemic optic neuropathy. Current methods of visual field testing all require the subject to indicate whether the stimulus is seen or not. Best Practice No 172: Pituitary Gland Pathology. 1 ). Pearls 6. Freda PU, Beckers AM, Katznelson L, Molitch ME, Montori VM, Post KD, Vance ML. In this case, the more negative a number, the more abnormal that point. This is then reported on a computerized printout in various ways, some numerical, others pictorial. 1, 2, 3 Pituitary or sella sequence magnetic resonance imaging (MRI) with and without contrast is the study of choice for most sellar and parasellar lesions, but high-resolution CTs with fine cuts (1.5-3 mm) have also been shown to be very helpful in the differential diagnosis especially if calcification is seen (e.g., craniopharyngioma or meningioma). Right homonymous hemianopia The tip of the occipital lobe, where the macular central homonymous hemifields are represented, often has a dual blood supply from terminal branches of the posterior cerebral artery and of the middle cerebral artery. This may present either as decreased central acuity or as a loss in peripheral visual fields.[24]. This is called Wilbrands knee and is responsible for the junctional scotoma in lesions of the posterior optic nerve. Monocular field loss, can be in a variety of patterns * Central / paracentral scotoma * Arcuate defect (Eg. An embolic infarction of either a distal MCA or PCA branch can result in exclusive ischemia of the tip of the occipital lobe, thereby producing only a small homonymous hemianopia if there is inadequate collateral circulation. View [6] The term, pituitary carcinoma is reserved forcases with metastatic spread, either local or systemic invasion, and comprise of <1% of tumors. What field defects results from ischemia limited to of the tip of an occipital lobe? 2. Moura FC, Gonalves AC, Monteiro ML. The result is a completely blind region of the patient's vision at the point of fixation. visual field loss indicates a prechiasmal pathology, while bilateral visual field loss indicates a chiasmal or retrochiasmal pathology. However, this effect is seen in any condition that causes delayed optic nerve conduction such as multiple sclerosis and retinal disorders. Chronic tumor compression can lead to optic atrophy. Visual Field Deficits. Altitudinal defect with near complete loss of the superior visual field, characteristic of moderate to advanced glaucomatous optic neuropathy (left eye). Two patterns of visual field loss occur when the lesion is secondary to an ischemic lesion in the territory of the choroidal arteries (anterior or posterior) (Fig. 1. The diplopia is binocular (only present when both eyes are open), and can have horizontal, vertical, or torsional components depending on the affected cranial nerve(s). Signs that you may have a visual field defect include: Bumping into things Knocking over objects when reaching Having difficulty reading Getting into a car accident What are the bilateral VF defect patterns? NAION) Optic Chiasm: * Nasal fibres (temporal visual field) decussate at the chiasm * Bitemporal hemianopia The numeric grid just to the right of the measurements of reliability is a presentation of the threshold level in decibels for all points checked in the patients visual field. 1. The patient. 11. Bilateral occipital lobe lesions will produce bilateral homonymous hemianopias, which may be asymmetric (Fig. They make up 30-50% of pituitary adenomas and are the most common clinically functional adenomas. A right RAPD (contralateral to lesion) because more fibers (53%) in the optic tract come from the opposite eyes nasal retina, having crossed in the chiasm. Macular sparing is visual field loss that preserves vision in the center of the visual field, otherwise known as the macula. Does the visual field defect involve one eye or two eyes? 2003. We report a case of bilateral superior altitudinal hemianopsia (BSAH) secondary to pituitary microadenoma related inferior optic chiasm damage. Clinical factors involved in the recurrence of pituitary adenomas after surgical remission: a structured review and meta-analysis. Most ophthalmologic complaints are secondary to mass effects caused by macroadenomas. A Homonymous hemianopia denser superiorly (pie in the sky), 1. 14. The adenoma grows precipitously because of the removal of the feedback inhibition of adrenal corticosteroids on the pituitary tissue. The features of acromegaly include characteristic coarsening of facial features (thick lips, exaggerated nasolabial folds, prominent supraorbital ridges, jaw enlargement), enlarged hands and feet, hirsuitism, and joint hypertrophy. Present stimuli consisting of dots of white light projected one at a time onto the screen, randomly presented (not moving). Prechiasmal damage to the visual pathway usually involves the optic nerve (e.g., optic neuritis , optic atrophy, AION , papilledema The densely granulated variant is more common and is usually basophilic, and the sparsely granulated variant is chromophobic. In: Schmidt-Erfurth, U., Kohnen, T. (eds) Encyclopedia of Ophthalmology. 4. Well, the visual field defect affects both eyes, which tells you that it is behind the optic chiasm. Bilateral altitudinal visual field defects usually result from prechiasmal pathology causing damage to both retinas or optic nerves and rarely from bilateral symmetric damage to the post chiasmal visual pathways. Diagnosis is clinical. We do not control or have responsibility for the content of any third-party site. These altitudinal visual-field defects (AVFDs) involved both nasal and adjacent temporal quadrants and respected the horizontal meridian. They derive from Pit-1 lineage and can express thyroid-stimulating hormone (TSH), which induces the thyroid gland to produce thyroid hormone (thyroxine). Therefore, the nasal visual field loss is more prevalent in NAION.9 Other types of visual field defects that can occur include nasal step, superior altitudinal field defect (observed in our patient), scotoma, temporal wedge defect and visual field constriction. Optic neuropathies typically produce nerve fiber bundle defects within the central 30 degrees of the visual field. 2. They are a diagnosis of exclusion from other tumors in the sella turcica area. These numbers are then converted to a gray scale representation of the field (upper right, Fig. 6. This may be: central (e.g. o [teenager OR adolescent ], Loss of all or part of the superior or inferior half of the visual field; does not cross the horizontal median, More common: Ischemic optic neuropathy, hemicentral retinal artery occlusion Central Retinal Artery Occlusion and Branch Retinal Artery Occlusion Central retinal artery occlusion occurs when the central retinal artery becomes blocked, usually due to an embolus. In men, the size of the adenoma is more likely to cause compressive symptoms while in women, there are more hormone imbalances. Part of Springer Nature. Causes. When we fixate with both eyes, there is superimposition of the central 60 degrees of visual fields in both eyes. [27], A few case reports have reported photophobia as the main presenting symptom in some patients with chiasmal disease.[29]. A congruent visual field defect presents with the same exact shape in the field of both eyes. The representation of this most peripheral 20 to 30 degrees is located in the anterior most portion of the contralateral occipital cortex. Of all conditions causing the chiasmal syndrome, pituitary adenomas are the most common (50-55%). The altitudinal defect can be unilateral or bilateral. [43] The outcome is affected by the severity of symptoms - for example, sudden ophthalmoplegia due to pituitary apoplexy would have a different result than a slow-growing prolactinoma. Diagnosis is clinical. There is no effective treatment. The WHO currently recommends against using the term atypical adenoma as there is no accurate prognosis Reliability measurements are reported in the upper left corner and include the number of fixation losses (2/13), false-positive errors (0%), and false-negative errors (3%) during the test. [1][3] Various articles have reported both male and female predilections. 1. Because this is not an autoimmune process, the hyperthyroid state induced by these adenomas is not associated with thyroid eye disease. 3. [2][6] Overall, it is estimated that in upwards of 25% of the population have pituitary adenomas although most of these are incidentally found. 3.16). What are the findings of a left optic tract lesion? These keywords were added by machine and not by the authors. [1] Periodic neuroimaging is also essential, as recurrence may occur even as late as 10 years post-surgery. 3.4.1 Anterior Visual Pathways [36], Cabergoline is a newer medication that also binds to D2 dopamine receptors. By repeating this in various parts of the visual field, an isopter can be plotted and then drawn on the screen with chalk or pins. A visual field test is part of a comprehensive eye exam and part of a neurological examination. Gigantism presents as a generalized increase in body size with disproportionately long arms and legs. Rosseau GL. A patient with altitudinal visual loss is more likely to have a carotid or cardiac embolic source compared with patients with diffuse or constricting patterns of vision loss. What are the findings of an occlusion of the posterior cerebral artery? 12. Preoperative MRI evaluation of pituitary macroadenoma: imaging features predictive of successful transsphenoidal surgery. Pituitary adenomas, which grow upward from the pituitary stalk, compress the chiasm from below, which preferentially involves the inferior, nasal, and macular nerve fibers. They tend to be macroadenomas at time of clinical diagnosis due to the subtle manifestations of excess growth hormone. What field defect results when a stroke affects the occipital lobe but spares the anterior portion of the occipital lobe? Grid: Present a square grid of lines and ask the patient to fixate on a central point and to draw any area in which the lines disappear (Fig. Lesions of the occipital lobe sparing this anterior most portion of the occipital cortex will spare the temporal crescent (Fig. The physiologic blind spot corresponds to the optic disc (which has no overlying photoreceptors) and is located approximately 15 degrees temporally in each eye. Treatment for the nonarteritic read more (usually nonarteritic), optic disk drusen, high myopia, Loss of all or part of the medial half of both visual fields; does not cross the vertical median, More common: Glaucoma Overview of Glaucoma Glaucomas are a group of eye disorders characterized by progressive optic nerve damage in which an important part is a relative increase in intraocular pressure (IOP) that can lead to irreversible read more , bitemporal retinal disease (eg, retinitis pigmentosa Retinitis Pigmentosa Retinitis pigmentosa is a slowly progressive, bilateral degeneration of the retina and retinal pigment epithelium caused by various genetic mutations. 3. Retinal diseases mostly cause central or paracentral scotomas . [18] Acidophil stem cell adenomas (ASCA) additionally have elevated GH and IGF-1. Crooke cell adenomas, another subset of corticotroph adenomas, have characteristic morphology on immunohistology stains with a ring of LMWK and PAS positive granules along the periphery. Altitudinal field defect. Visual field testing is useful when evaluating patients complaining of visual loss (especially when the cause of visual loss is not obvious after ophthalmic examination) or patients with neurologic disorders that may affect the intracranial visual pathways (e.g., pituitary tumors, strokes involving the posterior circulation, and traumatic brain Clinical Pearl: The earliest visual field defect in glaucoma is increased short term fluctuation. Medical and surgical management of pituitary adenomas require a multidisciplinary team. The filter causes the light conduction velocity to be slower, perceived by the brain as the object having false depth. What are the findings of a parietal lobe lesion? 2. Left homonymous hemianopia Lesion: in the right temporo-parietal region affecting the right optic radiation MRI shows haematoma of the right temporo . Clinical Pathways in Neuro-ophthalmology. What field defect results when a stroke only affects the anterior portion of the occipital lobe? Scotoma - this is a type of visual field defect. 1. Central, Cecocentral, Paracentral, Arcuate/Sector, Nasal Step, Altitudinal, Enlarged blind spots, Temporal Crescent Defect. Retro-chiasmal lesions almost always give rise to homonymous field defects with only one, exception. 3. Kreutzer J, Buslei R, Wallaschofski H, Hofmann B, Nimsky C, Fahlbusch R, Buchfelder M. Operative treatment of prolactinomas: indications and results in a current consecutive series of 212 patients. 6. Postsynaptic fibers from the lateral geniculate nucleus form the optic radiations, which separate into the inferior fibers (temporal lobe) and the superior fibers (parietal lobe) as they progress posteriorly toward the occipital cortex (Fig. The rule of congruency states that the more congruent the homonymous hemianopia, the more posterior the lesion. (A) Right optic disc shows mild superior disc oedema; left optic disc has more diffuse swelling and peripapillary haemorrhage. Radiation therapy (external beam or gamma-knife) is considered a second-line treatment. 1. Although the anatomical presence of Wilbrands knee is debated, junctional scotomas are observed clinically. Ironside JW. Sellar lesions and visual loss: key concepts in neuro-ophthalmology. Altitudinal defects occur in retinal vascular disease, glaucoma, and other disorders that affect the eye itself. When bilateral lesions of the retrochiasmal visual pathways produce a decrease in visual acuity, the degree of visual acuity loss is always symmetric in both eyes, unless there are other, more anterior, reasons for a decrease in visual acuity (e.g., asymmetric refractive errors, cataracts, or a superimposed asymmetric or unilateral retinopathy or optic neuropathy). Because more fibers in the optic tract come from the opposite eye (crossed fibers), a relative afferent pupillary defect (RAPD) is often observed in the eye contralateral to an optic tract lesion (see discussion later in this chapter). [6] These tumors stain positively with periodic acid-Schiff (PAS) because of the carbohydrates present in POMC, the precursor molecule to ACTH. The lower visual field falls on the superior retina (above the fovea). Borchert MS, Lessell S, Hoyt WF. [5] While both medications have similar mechanisms of action, the other medication may be tried if there is a minimal response from the first drug. The nasal visual field falls on the temporal retina. Tell the patient to fixate on a central spot. False Positive 33%. [1], Visual recovery following treatment of pituitary adenomas is largely dependent on pre-treatment visual acuity/visual fields/etc., age of patient, duration of symptoms, severity of visual defects, presence of optic atrophy, and size of the tumor. 3.22d) Rarely, patients with a lesion of the anterior occipital lobe may have a unilateral, contralateral visual field defect (see monocular temporal crescent). [1][2] Ophthalmologic findings typically involve visual field defects (e.g., optic neuropathy, junctional visual loss, bitemporal hemianopsia), although less commonly patients may also have efferent complaints (e.g., ocular motility deficits from cavernous sinus involvement, Nystagmus). 6. Why are altitudinal visual field defects common in ischemic optic neuropathies? Patients with secretory tumors may have systemic complaints that are associated with their corresponding hormonal imbalance. When an altitudinal visual field defect is a presenting feature, besides the usual vascular and compressive causes, optic neuritis should be remembered in the list of differential diagnoses. Present stimuli consisting of dots of white light projected one at a time onto the inner surface of the bowl, usually moving from the unseen periphery into the patients field of view. Use OR to account for alternate terms Cover one of the patients eyes. Driving and reading regular-sized print can be difficult. Because more fibers in the optic tract come from the opposite eye (crossed fibers), a relative afferent pupillary defect (RAPD) is often observed in the eye contralateral to an optic tract lesion (see discussion later in this chapter).