Vitreous

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Vitreous

Normal Anatomy

I. The transparent vitreous body, or hyaloid (Fig. 12.1), is one of the most delicate connective tissues in the body.

A. It occupies the posterior or largest compartment of the eye (~80% of the eye’s volume), filling the globe between the internal limiting membrane of the neural retina and the posterior lens capsule.

B. The structure is composed of a framework of extremely delicate, embryonic-like collagen filaments closely associated with a large quantity of water-binding hyaluronic acid.

Fig. 12.1 Normal vitreous. A, The vitreous compartment is completely filled by the vitreous body. The major components of the vitreous are hyaluronic acid and delicate collagenous filaments. B, On the left is a vitreous body stained with colloidal iron so that it appears blue. On the right, the tissue was first treated with hyaluronidase and no staining occurred, indicating that the blue-staining material on the left is hyaluronic acid. C, The other major components—the collagenous, delicate vitreous filaments (f)—are demonstrated by this electron micrograph of a shadow-cast preparation. The neural retina (r) occupies the diagonal lower left side and the filaments the diagonal upper right side. D, A ciliary-body melanoma has elevated the ora serrata region (o) so that it is clearly seen. Note that the attachment site (a) of the vitreous base appears as two white lines, one easily seen just anterior to the ora serrata and the other less easily seen just posterior to the ora serrata. This is the strongest attachment site of the vitreous body. The next strongest attachment site surrounds the optic nerve head, followed by a ring in the clivus of the anatomic fovea centralls (i, iris). (A, Armed Forces Institute of Pathology Neg. 57–1284. B and C, modified from Fine BS, Yanoff M: Ocular Histology: A Text and Atlas, 2nd edn. © Elsevier 1979.)

II. Embryology

A. Embryologically, the developing avascular secondary vitreous surrounds and compresses the vascularized primary vitreous into a tube or canal that extends from the optic disc to the back of the lens, forming the hyaloid canal (canal of Cloquet).

B. The hyaloid vessel, which atrophies and disappears before birth, passes through the canal.

C. Persisting remnants of the primary vitreous or hyaloid vessel produce congenital anomalies (see later), the most common being retention of tissue fragments on the back of the lens (Mittendorf’s dot; Fig. 12.2), retention of tissue on the nasal optic disc (Bergmeister’s papilla), and persistent primary vitreous (see Chapter 18).

Fig. 12.2 Mittendorf’s dot. A, Slit-lamp appearance of tiny white Mittendorf’s dot (m) at back of lens. B, Microscopic appearance of hyaloid vessel (h) as it approaches the posterior capsule (u, posterior umbilication of lens considered to be an artifactitious finding often seen in infants).

Congenital Anomalies

Persistent Primary Vitreous

I. Remnants of the primitive hyaloid vascular system, either anterior or posterior, may persist, or the entire hyaloid vessel from the optic disc to the back of the lens may remain.

Hyaloid vessel remnants are observed in more than 90% of infants of less than 36 weeks’ gestation and in more than 95% of infants weighing less than 5 pounds (2.275 kg) at birth.

A. Anterior remnants (see Fig. 12.2; see also Fig. 9.3)

1. The lenticular portion of the hyaloid artery may hang free in the vitreous from its lens attachment site.

2. Mittendorf’s dot is an opacity just below and nasal to the lens posterior pole at the lenticular attachment site of the hyaloid artery.

B. Posterior remnants (Fig. 12.3)

1. Vascular loops from the optic disc may remain within Cloquet’s canal.

2. Bergmeister’s papilla is the glial remnant of the hyaloid system at the optic disc. The papilla, which usually occupies the nasal portion of the optic disc, may appear as a solid mass of whitish tissue; as a delicate, ragged strand; or as a well-defined membrane stretching over the disc.

3. Congenital cysts, which are usually pearly gray, wrinkled, and translucent, are the cystic remains of the hyaloid system.

They usually float freely but may be attached to the optic disc or suspended by a pedicle. Some have been shown histologically to consist of gliotic retinal or vascular remnants, whereas others resemble pigment epithelial cells (i.e., choristoma of the primary hyaloid system).

Fig. 12.3 Posterior remnants. Posterior remnants may be mild, as in this Bergmeister’s papilla located on the nasal optic disc (A), or extreme, as in this posterior hyperplastic vitreous (B), which extends from the optic disc to the back of the lens (C). D, The enucleated eye shows posterior remnants of the hyaloid system over the nasal portion of the optic nerve head (b, Bergmeister’s papilla). E, Histologic section shows a Bergmeister’s papilla (b) in the form of a glial remnant of the hyaloid system.

Persistent Hyperplastic Primary Vitreous (Persistent Fetal Vasculature)

I. Anterior (see Chapter 18)

II. Posterior (congenital retinal septum; ablatio falciformis congenita)

A. Posterior persistent hyperplastic primary vitreous (PHPV; see Fig. 12.3) is most often unilateral and present at birth. Poor vision and strabismus are the most common presenting complaints.

B. Posterior PHPV consists of vitreous membranes extending from the disc usually toward the equatorial zone, posterior radial retinal fold (usually in the area of the vitreous membrane), disturbances of macular function, and neural retinal detachment.

Inflammation

Acute

See Chapter 3.

Chronic

See Chapters 3 and 4.

Vitreous Adhesions

Post Nonsurgical and Surgical Trauma

I. Vitreocorneal adhesions may cause corneal “touch” syndrome (see Fig. 5.5).

A. Corneal touch syndrome occurs when formed vitreous touches the endothelium of the posterior surface of the cornea, usually after a complicated cataract extraction, especially in the era of intracapsular cataract extraction.

B. The cornea becomes thickened and edematous in the region of touch.

II. Iridovitreal adhesions may lead to total posterior synechiae (seclusion of pupil) with resultant iris bombé, or they may form a membrane across the pupil (occlusion of pupil), or both.

III. Cyclovitreal adhesions may lead to a cyclitic membrane and subsequent neural retinal detachment.

IV. Vitreoretinal adhesions may lead to the macular vitreous traction syndrome (cystoid macular edema; Irvine–Gass syndrome; see Chapter 5) or to wrinkling of the internal limiting membrane, namely “cellophane” retina (see Figs. 11.43–11.45).

Traction of the vitreous on normal paravascular vitreoretinal attachment sites in an eye with a posterior vitreous detachment can cause neural retinal tears. Neural retinal tears tend to occur in clusters between the equator and the posterior border of the vitreous base.

V. White-without-pressure most likely is related to vitreoretinal adhesions. The areas of white-without-pressure may be migratory.

Postinflammation

See Chapters 3 and 4.

Idiopathic

Idiopathic vitreous adhesions may follow partial vitreoretinal separation (posterior vitreous detachment).

Vitreous Opacities

Hyaloid Vessel Remnants

Muscae volitantes are minute remnants of the hyaloid vascular system or detachments of small folds of poorly differentiated retinal tissue, usually present in the anterior vitreous.

Muscae volitantes also is a historical, obsolete term for acquired vitreous floaters.

Acquired Vitreous Strands and Floaters

I. Collapse and condensation of vitreous sheets with aging, especially in myopes, frequently cause the formation of strands and floaters.

II. Separation of the vitreous attachment to the optic disc after posterior vitreoretinal separation may cause a complete or incomplete ringlike floater (vitreous “peephole”; see subsection on vitreous detachment, later).

III. Symptomatic degenerative vitreous floaters may have a negative impact on the quality of life.

Inflammatory Cells

I. “Snowball” opacities (microabscesses) may occur with mycotic infections (especially with the mold fungi).

II. Whitish masses (“white balls”) may be seen inferiorly with vitreitis (e.g., sarcoidosis).

Macrophages and small T lymphocytes are the major cell types found in vitreous opacity samples diagnosed as inflammation.

III. Numerous vitreous opacities, foamy “Whipple” macrophages, may be found in persons with Whipple’s disease (Fig. 12.4).

A. Whipple’s disease is a disorder of men, usually older than 35 years of age.

1. The detection of the causative agent, Tropheryma whippelii, by polymerase chain reaction allows confirmation of the clinical diagnosis.

2. The gram-positive bacteria, Arthrobacter species, phylogenetically related to T. whippelii, may also be causative agents.

B. Arthritis, fever, serous effusions, cough, lymphadenopathy, and malaise may occur for several years preceding the intestinal malabsorption, steatorrhea, and cachexia.

C. Ocular findings, in addition to vitreous opacities, include inflammations and ophthalmoplegia.

D. Foamy macrophages containing periodic acid–Schiff (PAS)-positive cytoplasm may be found in intestinal and rectal mucosa, mesenteric and extra-abdominal lymphatic tissue, heart, lungs, liver, adrenals, spleen, serous membranes, neural retina, and vitreous.

1. In addition, intracellular and extracellular rod-shaped bacillary bodies and serpiginous membranes are found by electron microscopic examination of macrophages.

2. It is now assumed that the characteristic macrophages derive their PAS-positivity from ingested rod-shaped bacilli (Tropheryma whippelii) and also from their residue in autophagic vacuoles of the macrophages.

Fig. 12.4 Whipple’s disease. A, Inner retinal layers infiltrated by macrophages that exhibit pale blue cytoplasm and eccentric or paracentral small nuclei. Few macrophages are seen along internal limiting membrane (ILM). Epiretinal membrane has caused ILM to wrinkle. B, Decreased magnification shows neural retinal nerve fiber layer adjacent to macula containing myriad intensely PAS-positive macrophages. Outer and inner nuclear layers are relatively spared. C, Electron microscopy shows macrophage with serpiginous stacks of membranous structures intermixed with degenerating rod-shaped bacteria, both of which are encased in phagocytic vacuoles. D, Another macrophage shows almost equal admixture of membranous structures and degenerating bacteria. Inset depicts rod-shaped organism in longitudinal section and in cross-section. (From Font RL et al.: Arch Ophthalmol 96:1431, 1978. © American Medical Association. All rights reserved.)

Red Blood Cells

I. Red blood cells in the vitreous compartment (see Figs. 12.11 and 12.12) are most often caused by neural retinal tears but may have other causes. Red blood cells may be subvitreal (between vitreous body and internal limiting membrane of the neural retina) or intravitreal (within the vitreous body).

II. Hypoxia of the vitreous body may be demonstrated when blood enters it in a patient who has sickle-cell trait or disease.

A. Sickling and hemolysis of the erythrocytes increase toward the central vitreous, the most hypoxic area.

B. On histologic examination of a vitreous specimen or an enucleated globe, occasionally the diagnosis of sickle-cell trait or disease is made in a person not known previously to be so affected.

Iridescent Particles

I. Asteroid hyalosis (Benson’s disease; Figs. 12.5 and 12.6) consists of complex lipids embedded in an amorphous matrix containing mainly calcium and phosphorus and attached to the vitreous framework.

A. Diabetes mellitus is a major risk factor; other risk factors include systemic hypertension, atherosclerotic vascular disease, and hyperopia.

B. Asteroid hyalosis has the following clinical properties:

1. Asteroid bodies remain attached to collagenous framework and move only when the framework oscillates. They are seen as gold balls when viewed with side illumination (e.g., with the ophthalmoscope) and appear white with direct illumination (e.g., with the slit lamp).

2. The condition is usually unilateral and most common in the seventh and eighth decades of life. It is infrequently associated with neural retinal detachment.

Asteroid hyalosis may be a risk factor for the development of calcification of silicone lens implants.

C. Histologically, asteroid bodies consist of an amorphous matrix that is both PAS-positive and acid mucopolysaccharide-positive and contains birefringent, small crystals when viewed with polarized light. Electron microscopically, the bodies are composed of finely laminated ribbons of complex lipids, especially phospholipids, lying in a homogeneous background and intertwined with filaments of vitreous framework.