Ординатура / Офтальмология / Английские материалы / Ocular Pathology_6th edition_Yanoff, Sassani_2009

C.Amyloid may reach the vitreous directly from a ected retinal blood vessels.

D.Ecchymosis of lids, proptosis, ocular palsies, internal ophthalmoplegia, and neuroparalytic keratitis result from amyloid deposition in the lids and orbital connective tissues, muscles, nerves, and ganglia.

E.Glaucoma may be caused by amyloid deposition in the aqueous outflow areas.

F.Systemic amyloid deposition is widespread.

G.Histologically, a pale eosinophilic material is found in the vitreous that binds iodine and Congo red, demonstrates birefringence and dichroism (see later), shows metachromasia with metachromatic dyes such as toluidine blue and crystal violet, shows fluorescence after exposure to thioflavin-T, and has a filamentous ultrastructure.

Birefringence is the change in refractive indices with respect to light polarized in different directions through a substance. Dichroism is the property of a substance absorbing light polarized in a certain direction. When light is polarized at right angles to this direction, it is transmitted to a greater extent. In

contrast to birefringence, dichroism can be specific for a particular substance. Dichroism can be observed in a microscope with the use of either a polarizer or an analyzer, but not both, because the dichroic substance itself (e.g., amyloid) serves as polarizer or analyzer, depending on the optical arrangement. Amyloid is dichroic only to green light.

1.The deposited amyloid filaments found in tissues are portions of immunoglobulin light chains.

2.Filaments of amyloid are di cult to di erentiate from normal vitreous filaments.

3.The walls of retinal and choroidal blood vessels may be thickened by the amyloid material.

II.Familial amyloidotic polyneuropathy (FAP)

A.FAP is a hereditary form of systemic amyloidosis that involves vitreous (types I and II) and peripheral nerves.

1.In both FAP types I and II, the responsible protein is mutant transthyretin, designated amyloid AF.

In the majority of patients the valin-30 of transthyretin is replaced by methionine.

2.Type I FAP includes vitreous amyloidosis and an autonomic and peripheral neuropathy, most often a ecting the lower extremities.

FAP has been described in Portuguese, Swedish, and Japanese kindreds.

3.Type II FAP includes vitreous amyloidosis and peripheral neuropathy, most often a ecting the upper extremities first, along with a cardiomyopathy and sometimes a carpal tunnel syndrome.

FAP was first described in an Indian pedigree with Swiss origins.

4.Patients with types III and IV FAP do not acquire vitreous opacities, but do develop peripheral neuropathy, nephropathy, and peptic ulcers.

a.In type III FAP mutant apolipoprotein A1 is the responsible precursor protein.

b.In type IV FAP (also called Meretoja syndrome), mutant gelsolin is the responsible protein deposited.

Familial Exudative Vitreoretinopathy

I.Familial exudative vitreoretinopathy (FEV) is characterized by organized membranes in all quadrants of the vitreous.

A.Vitreoretinal traction results from the pull of the membranes.

B.Snowflakelike opacities are present in the vitreous body.

C.The vitreous is usually detached posteriorly.

II.Frequently encountered are peripheral neural retinal exudates, localized neural retinal detachment often forming a broad fold temporally from the disc, and peripheral neural retinal neovascularization with recurrent vitreous hemorrhages.

Results of fluorescein angiography suggest a primary abnormality in the peripheral retinal circulation as the cause of the entity.

III.Slowly progressive ocular changes may ultimately lead to a condition that mimics certain aspects of retinopathy of prematurity, Coats’ disease, and peripheral uveitis.

IV. FEV is genetically heterogeneous: X-linked; autosomaldominant (most common); and autosomal-recessive types have been described.

A.One X-linked and two autosomal-dominant loci have been mapped: EVR1 on 11q, EVR2 on Xp, and EVR3 on 11p.

B.The defective gene on EVR1 locus is FZD4.

Other autosomal-dominantly inherited retinal disorders include autosomal-dominant vitreoretinochoroidopathy (ADVIRC; see later), autosomal-dominant neovascular inflammatory vitreo-

retinopathy (ADNIV; see later), autosomal-dominant cystoid macular dystrophy (autosomal-dominant macular edema; see p. 443 in Chapter 11), snowflake degeneration (see p. 440 in Chapter 11), and Wagner’s and Stickler’s syndromes (see pp. 439 and 440 in Chapter 11). FEV may also have an X-linked recessive inheritance pattern, carried on Xq 21.3 or Xp 11, and perhaps an allelic variant of the Norrie’s disease gene.

Autosomal-Dominant Vitreoretinochoroidopathy

(ADVIRC, Peripheral Annular Pigmentary

Dystrophy of the Retina)

I.ADVIRC clinically shows a stationary or slowly progressive, circumferential (360°), bilateral and symmetric involvement of a coarse, peripheral hyperpigmentation and hypopigmentation of the fundus; a relatively discrete posterior border occurs in the region of the equator.

A.The retinopathy is associated with fibrillar condensation of the vitreous and superficial and deep, yellowishwhite, punctate opacities in the fundus.

B.Other ocular findings include retinal vascular attenuation, transudation, and neovascularization; cystoid

macular edema; choroidal atrophy; and cataract formation.

II.Histologically, disorganization of the peripheral neural retina occurs with focally atrophic retinal pigment epithelium (RPE).

A.Altered RPE cells surround retinal vessels and line the internal limiting membrane.

B.The equatorial neural retina shows an unusual multifocal loss of photoreceptors.

C.An extensive epiretinal membrane consists of condensed vitreous, cellular debris, and layers of Müller cells.

Autosomal-Dominant Neovascular Inflammatory

Vitreoretinopathy (ADNIV)

I. ADNIV clinically resembles ADVIRC, except that in the initial stage it shows a characteristic selective reduction of the electroretinogram b-wave amplitude; in addition, the pigmentary changes are less distinctive in ADNIV than in ADVIRC.

II.Cystoid macular edema, vitreous hemorrhage, tractional neural retinal detachment, and neovascular glaucoma can cause a profound loss of vision.

Erosive Vitreoretinopathy

I.Erosive vitreoretinopathy is characterized by pronounced vitreous abnormalities, complicated neural retinal detachments, and a progressive pigmentary retinopathy.

A.The condition is inherited in an autosomal-dominant pattern. Mutations that cause erosive vitreoretinopathy (and also Wagner’s disease) are linked to markers on the long arm of chromosome 5 (5q13–14).

B.Clinically, nyctalopia, progressive visual field loss, marked vitreous syneresis, progressive atrophy of the

RPE, and combined traction–rhegmatogenous neural retinal detachments are seen.

1.Previously normal-appearing RPE seems to thin or erode (hence the term erosive) in younger patients, allowing increased visualization of choroidal vessels.

2.Advanced cases show equatorial areas apparently devoid of RPE.

3.Electroretinography demonstrates di use rod–cone dysfunction.

High myopia, epiphyseal dysplasia, orofacial anomalies, and systemic manifestations characteristic of other vitreoretinopathies are absent.

C.No histologic studies are available.

Knobloch Syndrome

I.Knobloch syndrome is characterized by high myopia, vitreoretinal degeneration, retinal detachment, and a localized defect in the occipital region of the skull.

A.It is inherited as an autosomal recessive

B.A mutation occurs in the COL1A1 gene, which encodes collagen XVII and its normal product endostatin, an

inhibitor of angiogenesis

II. Endostatin is absent from the serum.

III.Persistent hyperplastic primary vitreous may be present (see p. 747 in Chapter 18).

VITREOUS HEMORRHAGE

Definitions

I. Subvitreal hemorrhage (Fig. 12.11)—blood is present between the internal limiting membrane of the neural retina, and the posterior “face” of the vitreous and takes weeks to months to clear. This type of hemorrhage is commonly seen in diabetic patients.

II.Intravitreal hemorrhage (Fig. 12.12; see Fig. 12.11)—blood is present in the vitreous body and takes many months to years to clear.

III.Subhyaloid hemorrhage—this is identical to subvitreal hemorrhage, but use of the term clinically may be confusing.

Sometimes the term subhyaloid hemorrhage is used clinically to describe an intraretinal submembranous hemorrhage (i.e., a hemorrhage located mainly between the nerve fiber layer and the internal limiting membrane of the neural retina; see Figs 12.12 and 11.42D).

Causes

I.Causes include blood dyscrasias; choroidal hemorrhage with extension; diabetic retinopathy; Eales’ disease; hypertensive retinopathy; juvenile retinoschisis; malignant melanoma; metastatic intraocular tumors; neural retinal neovascularization from any cause; neural retinal tears;

retinal angiomas; retinoblastoma; subneural retinal neovascularization; Terson’s syndrome; sickle-cell retinopathy; subarachnoid hemorrhage; trauma; uveitis; and vitreoretinal separation.

II.Terson’s syndrome

A.Terson’s syndrome consists of hemorrhage into the vitreous compartment associated with intracranial, subarachnoid, or subdural hemorrhage.

Vitreous hemorrhage develops in approximately 16% to

17% of patients in whom spontaneous subarachnoid hemorrhage occurs.

B.Vitreous hemorrhage frequently obscures visualization of the fundus.

1.When visualization of the neural retina is possible, multiple preneural, intraneural (usually subinternal limiting membrane), and subneural retinal hemorrhages are often seen.

2.Other findings include epiretinal membranes, proliferative vitreoretinopathy, pigmentary macular

changes, and perimacular neural retinal folds similar to the folds seen in the battered-baby (shaken-baby) syndrome.

Complications

I.Organization

A.Membranes may lie on the internal surface of the neural retina (i.e., epiretinal) and cause a cellophane retina or fixed retinal folds (see Figs 11.43 to 11.45).

B.Many of the delicate epiretinal (on the retinal surface) and preretinal (elevated from the retinal surface) membranes, especially those of the macular and paravascular regions, are believed to form from inward migration and proliferation of the various small glial cells normally present in the nerve fiber and ganglion cell layers.

1.Other cells, such as RPE cells, fibrocytes, and myo-

fibroblasts, can also be found.

2.As the membranes shrink or contract, fixed folds of the retina develop (see p. 467 in Chapter 11).

C.When fibrous RPE or glial membranous proliferations on the internal or external surface of the neural retina are associated with vitreous retraction, a neural retinal detachment and new neural retinal holes may result.

D.When the membranous process is extensive and associ-

ated with a total neural retinal detachment, it is called proliferative vitreoretinopathy (PVR); the older terminologies were massive vitreous retraction and massive periretinal proliferation.

1.PVR may follow perforating trauma, neural retinal detachment, and surgical manipulation.

2.Although PVR most often develops posteriorly and equatorially, it may also occur anteriorly, where it results in anterior dragging of the peripheral neural retina.

3.PVR probably represents a tissue-reparative process and can be thought of as nonvascular granulation tissue.

Some evidence suggests that fibronectin may mediate the initial events in epiretinal membrane formation and

that vitronectin may modulate the adhesion mechanisms in established membranes. Transforming growth factor-β2 levels are increased in eyes that have intravitreal fibrosis associated with PVR, and the levels appear to correlate with the severity of PVR.

E.Histologically, glial, fibrous, or RPE membranes, or any combination, are seen on the internal, external, or both surfaces of the retina.

1.T lymphocytes and macrophages may be present in the membranes.

2.The membrane stroma or matrix is composed pri-

marily of types I, II, and III collagen, accompanied focally by types IV and V collagen, laminin, and heparan sulfate.

II. Hemolytic (ghost cell) glaucoma (see p. 647 in Chapter 16)

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NORMAL ANATOMY

I.The optic nerve is made up of a number of components

(Figs 13.1 and 13.2).

A.The major component is myelinated nerve fibers or axons (white matter).

1.The axons of the optic nerve are extensions of the retinal ganglion cells whose unmyelinated axons form much of the nerve fiber layer of the neural retina.

2.The axons or “nerve fibers” then enter the optic disc by making a sharp turn, where they continue as a series of fascicles or bundles, separated from one another by helical columns of glial cells (astrocytes) and vascular connective tissue septa, to form the optic nerve.

3.The optic nerve becomes myelinated as it traverses the lamina cribrosa scleralis, doubling its diameter

from approximately 1.5 mm at the optic disc to 3 mm as it leaves the scleral canal posteriorly.

The lamina cribrosa is a series of trabeculae, contiguous with the choroidal (lamina cribrosa choroidalis—glial) and scleral (lamina cribrosa scleralis—vascularized collagen) coats of the eye. The trabeculae form a criss-cross pattern outlining “pores” through which the nerve fiber bundles pass. The myelinated orbital portion of the optic nerve can be considered more a tract of the brain than a true cranial nerve. The optic nerve is continuous at one end with the retina and at the other end with the brain, making it vulnerable to a variety of both ocular and central nervous system (CNS) diseases.

B.All the CNS meningeal sheaths (dura, arachnoid, and pia) are present and surround the orbital portion of the optic nerve.

The subarachnoid space of the optic nerve is continuous with that of the intracranial contents.

An elevation of intracranial pressure, therefore, is directly transmitted to the subarachnoid space surrounding the optic nerve and contained within its dural sheath.

C.The capillary blood supply to the anterior 2 to 3 mm of the optic nerve (intrachorioscleral portion) is derived exclusively from the ophthalmic artery through two sources.

1.One source of blood supply, the major supply, consists of peripapillary choroidal branches, which are fed through the choroidal circulation by the short posterior ciliary arteries.

2.Another source, albeit of much less significance, is the perineural plexus in the most anterior portions of the subarachnoid space surrounding the optic nerve.

D.The capillary blood supply of the remaining ophthalmic artery vessels enters the nerve from the pial surface in a symmetric, radially distributed pattern.

E.The central retinal artery first enters the optic nerve approximately 0.8 to 1.5 cm behind the globe.

II.The optic nerve is approximately 30 mm long, longer than the distance from the back of the eye to the optic canal, and so takes a somewhat sinuous course through the posterior orbit.

CONGENITAL DEFECTS AND

ANATOMIC VARIATIONS

Aplasia

I.Aplasia of the optic nerve (Fig. 13.3) is rare, especially in eyes without multiple congenital anomalies.

II.Most cases occur as unilateral disorders in otherwise healthy persons, although bilateral cases have been reported.

III. Most probably, the retinal ganglion cells fail to develop properly. Alternatively, the optic nerve aplasia may result from abnormal invagination of the ventral fissure.

IV. Histology

A.The optic nerve, optic nerve head, nerve fibers (axons) in the retinal nerve fiber layer, and retinal vessels are absent.

B. The retinal ganglion cell layer is diminished or absent. When present, the retinal ganglion cells appear

undi erentiated, lacking axons or dendrites.

Hypoplasia

I.Although rare, hypoplasia (underdevelopment of the optic nerve) is more common than aplasia (congenital absence of the optic nerve).

A.Hypoplasia of the optic nerve is a major cause of blindness in children.

B.In optic nerve hypoplasia, a small optic disc with central vessels is present.

The term optic nerve hypoplasia should be reserved for cases that show hypoplasia as the main or sole anomaly of the nerve (e.g., colobomas of the optic nerve usually show hypoplastic

nerves, but the main event is the coloboma, not the hypoplasia). Also, in those situations where multiple anomalies of the eye or brain or both are present, it is difficult to determine whether the optic nerve is hypoplastic (primary failure of development) or atrophic (secondary degeneration). A hypoplastic or atrophic optic nerve may be found in association with grossly malformed eyes (e.g., microphthalmos) or with deformities of the CNS (e.g., hydrocephalus). Hypoplasia of the optic nerve is also a prominent feature of septo-optic dysplasia (de Morsier syndrome), which consists of optic nerve hypoplasia, absence of the septum pellucidum, and pituitary insufficiency.

II.Optic nerve hypoplasia may be unilateral or bilateral, with or without optic foramina radiographic abnormalities, causes subnormal vision, and shows a decreased number of optic nerve axons.

High-resolution magnetic resonance imaging is an excellent method to detect small optic nerves.

III. Visual acuity is generally markedly decreased.

IV. The cause is failure of the retinal ganglion cells to develop normally.

A.Because the optic stalk is invaginated by mesoderm, the central retinal artery and vein are present on the disc.

B.Histologically, the nerve shows partial or complete absence of neurites.

Dysplasia

I.Dysplasia or abnormal development of the optic nerve is usually associated with other optic nerve anomalies such as colobomas and also with gross malformations of the eye.

II.Histologically, a marked disorganization of the nerve occurs, usually accompanied by a partial absence of neurites.

Fig. 13.2 Vascular supply of the anterior optic nerve. Schematic shows that capillaries in laminar region derive from two sources: choroid via short posterior ciliary arteries, and pial plexus. Considerable individual variations occur. (From Hart WM, Jr: In Podos SM, Yanoff M, eds:

Textbook of Ophthalmology, vol. 6. London, Mosby, 1994:1.14. © Elsevier 1994.)

Optic disc dysplasia may be associated with transsphenoidal encephalocele (e.g., when seen with V- or tongue-shaped retinochoroidal anomaly or with the morning-glory syndrome).

Anomalous Shape of Optic Disc and Cup

I.Minor disturbances

A.Oval discs (vertically, horizontally, or obliquely elongated) are common.

B.They are congenital and nonprogressive.

A normal disc may appear abnormal when viewed with the direct ophthalmoscope in an eye with a significant degree of astigmatism.

II. Myopia (see p. 504 in this chapter and p. 423 in Chapter

11)

III.Congenital excavation of optic disc (i.e., an exaggeration of physiologic cup)

A.It almost never extends as far as the edge of the disc

(when it does, it usually does so temporally).

Major retinal blood vessels often pass through the substance of the optic rim.

B.It is nonprogressive.

C.Histologically, the optic nerve is normal except for an enlarged physiologic cup in the optic disc. Often the diameter of the choroidal portion of the optic nerve is somewhat larger than normal.

IV. Pseudoneuritis or pseudopapilledema (i.e., the opposite of congenital excavation)

A.In pseudoneuritis, the nerve fibers and glial tissues are

“heaped up.”

B.It is nonprogressive and lacks dilatation of the veins, hemorrhages, or exudates.

C.Often it is associated with hypermetropia or drusen of the optic nerve head.

D.Histologically, the optic nerve is normal except for a smaller than usual or absent physiologic cup in the optic disc.