Of the Human Visual Pathway

Nearly a half of all cortical neurons are devoted to the processing of visual information. The afferent visual pathway from the retina to the primary visual cortex has four neuronal elements ( Fig. 3.1). First neuron photoreceptors Second neuron bipolar cells Third neuron retinal ganglion cells (and their axonal processes, including the chiasm and optic tracts) Fourth neuron geniculocalcarine neurons Surface area of the cerebral retina is about 30 cm2 Fig. 3.1. Schematic diagram of the human...

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MLF lesion (left internuclear ophthalmoplegia) -MLF lesion and PPRF lesion and or N. VI lesion (right one-and-a-half-syndrome) MLF lesion (left internuclear ophthalmoplegia) -MLF lesion and PPRF lesion and or N. VI lesion (right one-and-a-half-syndrome) Fig. 11.5. a,b Supranuclear and nuclear structures of the ocular motor system. View of the translucent brainstem from behind. The impulse for right gaze is generated in the right PPRF. The signal is transmitted to the right abducens nucleus...

With cogwheel phenomenon

Fig. 21.5 a Testing of the muscle tone around the elbow joint by passive manipulation during maximal relaxation of the muscles. b Diagram of important pathological findings the pocketknife phenomenon (fading of resistance when under steady pressure), and cogwheeling (joint rigidity with repeated, brief, and uniform increases in tonus over the entire range of motion of the joint) in case of muscle rigidity in Parkinson's disease Table 21.10. The differential diagnosis of central and peripheral...

Absolute Visual Field

One examined retinal location with two threshold reversals DLS Differential luminance sensitivity (decibel) Several presentations only for assessment of depth Fig. 4.8. Testing strategies used with automated static perimetry. Left The principle of threshold static perimetry, in which the threshold for perception of a stimulus is determined by sequentially presenting test objects with stimulus values that lie just above or below a putative value at a given location, and threshold is defined as a...

Traumatic Optic Neuropathy Definition

A traumatic optic neuropathy is one caused by trauma to the optic nerve, most frequently in the setting of a traffic accident with cranial and or midface fractures. Traumatic optic neuropathy results primarily from indirect injury, rather than by direct crushing or tearing mechanisms. A direct blow to the eye can cause an avulsion of the optic nerve more properly called an expulsion . The mechanism appears to be one of a sudden, explosive increase in intraocular pressure with rupture of the...

Microvascular Oculomotor Pareses

Microvascular ischemia of the oculomotor nerve arises from small-vessel disease of the vasa vasorum supplying the third nerve. It is the most common cause of oculomotor paresis in most ophthalmic practices. Though not specific, the presentation is characteristic, including acute onset of diplopia, complete or partial palsies of the muscles supplied by the third nerve, sparing of the pupillary sphincter, and ipsilateral retrobulbar and or temporal pain. The pain is thought to stem from the acute...

Fascicular Paralysis of the Oculomotor Nerve

Due to the separation of the third nerve fascicles as they leave their nuclear complex, pass through the red nucleus, substantia nigra, and the pyramidal tracts to exit the brain-stem into the interpeduncular fossa, damage in this region often results in incomplete paralysis. The pupil may be spared, or an isolated paralysis of elevation may be found. Even patterns of isolated superior or inferior divisional palsies of the third nerve can arise from disease located within the midbrain....

Functional Loss of Both Vestibular Organs

Caloric testing of vestibular function. Fixation is excluded, e.g., by means of Frenzel glasses. With the head reclined, the external auditory canal on one side is irrigated with water at 44 C. This warms the endolymph in the lateral sector of the horizontal canal, whereas the endolymph in the medial sector of the horizontal canal remains unaffected. The warmer fluid in the lateral sector tends to rise, setting up a weak circulation within the canal. This tiny circulation suffices...

T Pearl

Recovery of the optic disc appearance after correction of the elevated intracranial pressure can take many weeks. A child with hydrocephalus - of whatever cause - is threatened with blindness if chronic papilledema develops. All such children require regular ophthalmic follow-up examinations to monitor their fundus appearance. Unique Nature of Pseudotumor Cerebri Benign Intracranial Hypertension Each of these names is misleading at best. The term pseudotumor originated at a time when...

Clinical Features of Graves Disease

Graves' disease also called thyroid ophthalmopathy, dys-thyroid ophthalmopathy, or endocrine orbitopathy is an autoimmune disease that commonly, though not always, is associated with hyperthyroidism. It is accompanied by a broad spectrum of signs and symptoms of orbital inflammation. Chief among these is exophthalmos. Graves' disease is the most common cause of exophthalmos among Fig. 9.5. A patient with Graves' disease. Striking proptosis, left more than right, with bilateral retraction of...

Oculomotor Apraxia Definition

Oculomotor apraxia describes an eye movement disorder characterized by loss of or severely diminished volitional saccades with retention of the fast phases of vestibular nystagmus. Reflexive saccades stimulated by objects of interest in the peripheral visual field may be disordered or normal. Congenital oculomotor apraxia Cogan's syndrome manifests in newborn infants. During the first 3 months of life, affected infants are unable to look toward objects held out to them, and may be mistakenly...