Ординатура / Офтальмология / Английские материалы / Ophthalmology A Short Textbook_Lang_2000

Functional symptoms include a large central scotoma with a peripherally limited visual field. This will lead to significant loss of vision within a few months, although the remaining vision will not decrease any further.

There is no treatment.

Behr’s disease (infantile recessive optic atrophy). This is also a disorder involving both optic nerves. However, in contrast to Leber’s atrophy there are additional neurologic symptoms. These may include ataxia and mental retardation. The disease is an inherited autosomal recessive disorder and manifests itself in early childhood.

Ophthalmoscopy will reveal progressive optic atrophy with severe loss of visual acuity but without complete blindness.

There is no treatment.

Waxy pallor optic atrophy. This disorder (Fig. 13.16) is associated with tapetoretinal degeneration, such as retinitis pigmentosa.

Ophthalmoscopy will reveal an optic disk with a wax-like pallor that is shallow with a well defined margin. There will be severe thinning of the central retinal vessels. The cause of the wax-like yellow color is not known.

There is no treatment.

13.4.2Optic Nerve Pits

An optic nerve pit (Fig. 13.17) is characterized by a round or oval grayish depression in the papillary tissue that does not compromise the margin of the optic disk. These pits are usually found in an inferior temporal location, although they do occur elsewhere. In 85% of all cases, one eye is affected.

Waxy pallor optic atrophy.

Fig. 13.16 Waxy pallor optic atrophy is associated with tapetoretinal degeneration.

384 13 Optic Nerve

Optic nerve pits.

Fig. 13.17 These are oval grayish temporal depressions in the papillary tissue (arrow).

Several pits in one optic disk have been described. Serous retinal detachment occurs in 25% of all cases, depending on the location of the pit. Where the detachment affects the macula, a significant loss of visual acuity will result that will prove very difficult to manage with laser surgery. Otherwise optic nerve pits are an incidental finding without any functional deficit. They are considered to be rudimentary colobomas.

Optic disk coloboma.

Fig. 13.18 The optic disk is enlarged with a fun- nel-shaped depression with whitish tissue and a peripapillary pigment ring. The retinal vessels do not branch from a central venous or arterial trunk.

13.5 Tumors 385

13.4.3Optic Disk Coloboma (Morning Glory Disk)

An optic disk coloboma (Fig. 13.18) is the result of incomplete closure of the embryonic optic cup. The optic disk is enlarged with a funnel-shaped depression with whitish tissue and a peripapillary pigment ring. The retinal vessels extend outward across the margin of the disk in a radial pattern without a central trunk vessel. Patients with optic disk coloboma often have decreased visual acuity and visual field defects.

13.5Tumors

Optic nerve tumors are classified as intraocular or retrobulbar tumors. Intraocular tumors are rare.

13.5.1Intraocular Optic Nerve Tumors

Melanocytoma (Fig. 13.19): These are benign pigmented tumors that primarily occur in blacks. The color of the tumor varies from gray to pitch black. It is often eccentric and extends beyond the margin of the optic disk. In 50% of all cases, one will also observe a peripapillary choroidal nevus. Visual acuity is usually normal, although discrete changes in the visual field my be present.

Astrocytoma (Fig. 13.20): Astrocytomas appear as white reflecting “mulberry” masses that can calcify. Their size can range up to several disk diameters. The tumor is highly vascularized. Visual field defects can result where the tumor is sufficiently large to compress the optic nerve. Astrocytomas

Melanocytoma.

Fig. 13.19 Benign tumor of the optic disk that represents a special form of nevus (arrow).

386 13 Optic Nerve

Astrocytoma in tuberous sclerosis (Bourneville’s disease).

Fig. 13.20 Whitish, “mulberry” tumor on the superior margin of the optic disk (arrow).

occur in tuberous sclerosis (Bourneville’s disease) and neurofibromatosis (Recklinghausen’s disease).

Hemangioma (Fig. 13.21): Capillary hemangiomas are eccentric, round orange-colored vascular deformities on the optic disk (von Hippel disease). They may occur in association with other angiomas, for example in the cerebellum (in von Hippel-Lindau disease).

Capillary hemangioma in von Hippel disease.

Fig. 13.21 Eccentric capillary vascular deformity on the optic disk (arrow).

13.5 Tumors 387

13.5.2Retrobulbar Optic Nerve Tumors

The most common retrobulbar optic nerve tumors are gliomas and meningiomas. Symptoms include a usually slow loss of visual acuity with exophthalmos. Ophthalmoscopy will reveal descending primary atrophy of the optic nerve. Meningioma of the sheath of the optic nerve is typically accompanied by the formation of opticociliary shunt vessels with compression of the central retinal vessels.

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14 Visual Pathway

Oskar Gareis and Gerhard K. Lang

14.1Basic Knowledge

The anatomy of the visual pathway may be divided into six separate parts (Fig. 14.1):

1.Optic nerve: This includes all of the optic nerve fiber bundles of the eye.

2.Optic chiasm: This is where the characteristic crossover of the nerve fibers of both optic nerves occurs. The central and peripheral fibers from the temporal halves of the retinas do not cross the midline but continue into the optic tract of the ipsilateral side. The fibers of the nasal halves cross the midline and there enter the contralateral optic tract. Along the way, the inferior nasal fibers travel in a small arc through the proximal end of the contralateral optic nerve (the anterior arc of Wilbrand). The superior nasal fibers travel in a small arc through the ipsilateral optic tract (the posterior arc of Wilbrand).

3.Optic tract: This includes all of the ipsilateral optic nerve fibers and those that cross the midline.

4.Lateral geniculate body: The optic tract ends here. The third neuron connects to the fourth here, which is why atrophy of the optic nerve does not occur in lesions beyond the lateral geniculate body.

5.Optic radiations (geniculocalcarine tracts): The fibers of the inferior retinal quadrants pass through the temporal lobes; those of the superior quadrants pass through the parietal lobes to the occipital lobe and from there to the visual cortex.

6.Primary visual area (striate cortex or Brodmann’s area 17 of the visual cortex): The nerve fibers diverge within the primary visual area; the macula lutea accounts for most of these fibers. The macula is represented on the most posterior portion of the occipital lobe. The central and intermediate peripheral regions of the visual field are represented anteriorly. The temporal crescent of the visual field, only present unilaterally, is represented farthest anteriorly.

Other connections extend from the visual cortex to associated centers and oculomotor areas (parastriate and peristriate areas). Aside from the optic tract there is also another tract known as the retinohypothalamic tract This

14.2 Examination Methods 391

tract is older in evolutionary terms and diverges from the optic chiasm. It transmits light impulses for metabolic and hormonal stimulation to the diencephalon and pituitary gland system and influences the circadian rhythm.

14.2Examination Methods

Visual field testing (perimetry): This is the most important test for visual pathway lesions. Because it permits one to diagnose the location of the lesion, it is also of interest from a neurologic standpoint. The “visual field” is defined as the field of perception of the eye at rest with the gaze directed straight ahead. It includes all points (objects and surfaces) in space that are simultaneously visible when the eye focuses on one point.

The examination is performed on one eye at a time. The principle of the test is to have the patient focus on a central point in the device while the eye is in a defined state of adaptation with controlled ambient lighting (see below). Light markers appear in the hemisphere of the device. The patient signals that he or she perceives the markers by pressing a button that triggers an acoustic signal.

There are two types of perimetry.

1.Kinetic perimetry. Hemispheric Goldmann or Rodenstock perimeters are used for this test (Fig. 14.2). Kinetic perimetry involves moving points of light that travel into the hemisphere from the periphery. Light markers of identical size and intensity produce concentric rings of identical perception referred to as isopters. The points of light decrease in size and light intensity as they move toward the center of the visual field, and the isopters become correspondingly smaller (Fig. 14.2b). This corresponds with the sensitivity of the retina, which increases from the periphery to the center.

The advantage of kinetic perimetry is the personal interaction between physician and patient. This method is especially suitable for older patients who may have difficulties with a stereotyped interaction required by a computer program. Specific indications for kinetic perimetry include visual field defects due to neurologic causes and examinations to establish a disability (such as hemianopsia or quadrantic anopsia).

2.Static perimetry. This is usually performed with computerized equipment such as the Humphrey field analyzer (Fig. 14.3) or Octopus 2000, although a Goldmann or Rodenstock hemispheric perimeter can also be used for static testing of the visual field. In static perimetry, the light intensity of immobile light markers is increased until they are perceived. The intensity threshold continuously increases from the macula, with the highest sensitivity, to the periphery. A variety of different computer programs can be selected depending on the specific clinical setting. These include the outer margins or the 30 degree visual field in glaucoma (Fig. 14.3b).

392 14 Visual Pathway

Goldmann hemispheric perimeter and visual field findings.

Fig. 14.2 a The patient focuses with one eye on a black dot in the middle of the hemisphere. As soon as the patient notices the light marker moving in from the periphery, he or she presses a button that triggers an acoustic signal. The examiner sits behind the hemisphere. From there, the examiner controls the light marker and records which points the patient recognizes.

Continued !

Other examination methods:

Pupillary findings.

Pupillary light reflex.

Visual evoked potential.

CT or MRI to diagnose causes.