Neural (Sensory) Retina

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11

Neural (Sensory) Retina

Normal Anatomy

I. The neural retina (Figs. 11.1–11.3) is a highly specialized nervous tissue, in reality a part of the brain that has become exteriorized.

Although the terms neural retina and sensory retina are proper, in this chapter, because of “customary” usage, the terms retina, neural retina, and sensory retina are often used interchangeably. The terms refer to all the “layers” of the retina exclusive of its retinal pigment epithelium (RPE), which is discussed separately (see Chapter 17). The term neurosensory retina is redundant.

A. Traditionally, the retina, from the RPE externally to the internal limiting membrane internally, is divided into 10 layers (see Fig. 11.2B).

B. The neural retina has the equivalent of both white matter (plexiform and nerve fiber layers) and gray matter (nuclear and ganglion cell layers).

C. The glial cells are represented mostly by large, all-pervasive, specialized Müller cells and, less noticeably, by small astrocytes (and possible oligodendrocytes) of the inner neural retinal layers.

D. As in the brain, a vasculature is present in which the endothelial cells possess tight junctions, producing a blood–retinal barrier.

image
Fig. 11.2 Normal retina. A, The anatomic macula (posterior pole) is recognized by the multilayered ganglion cell layer, present between the inferior and superior retinal vascular arcades, and from the optic nerve temporally for a distance of approximately four disc diameters (16 mm). This periodic acid–Schiff stain clearly shows the internal limiting (basement) membrane. B, The retina consists of two major parts: the retinal pigment epithelium and the neural (sensory) retina. The latter can be divided into nine layers: (1) photoreceptors (rods and cones); (2) external limiting membrane [terminal bar (zonulae adherentes)—attachment sites of adjacent photoreceptors and Müller cells]; (3) outer nuclear layer (nuclei of photoreceptors); (4) outer plexiform layer (axonal extensions of photoreceptors), which contains the middle limiting membrane (desmosome-like attachments of photoreceptor synaptic expansions); (5) inner nuclear layer (nuclei of bipolar, Müller, horizontal, and amacrine cells); (6) inner plexiform layer (mostly synapses of bipolar and ganglion cells); (7) ganglion cell layer (here a single layer of contiguous cells, signifying a region outside the macula); (8) nerve fiber layer (axons of ganglion cells); and (9) internal limiting membrane (basement membrane of Müller cells) (nr, neural retina; c, choroid; im, internal limiting membrane; nf, nerve fiber layer; gc, ganglion cell layer; ip, inner plexiform layer; in, inner nuclear layer; mm, middle limiting membrane; op, outer plexiform layer; on, outer nuclear layer; em, external limiting membrane; pr, photoreceptors; rpe, retinal pigment epithelium). C, Increased magnification of the photoreceptors shows the inner segments to be cone- and rod-shaped. (B, Modified with permission from Fine BS, Yanoff M: Ocular Histology: A Text and Atlas, 2nd edn. Hagerstown, MD, Harper & Row, 1979 : 113. © Elsevier 1979; C, courtesy of Dr. RC Eagle, Jr.)

II. Foveomacular region of the neural retina

A. Clinicians often confuse the proper use of the terms fovea, macula, and posterior pole (see Fig. 11.3).

1. For convenience and practicality, the three clinical terms correspond best to the three anatomic terms foveola, fovea (centralis), and area centralis (often called histologic macula). The clinical fovea, therefore, equals the anatomic foveola; the clinical macula equals the anatomic fovea; and the clinical posterior pole equals the anatomic area centralis (“histologic macula”).

2. The anatomic fovea or fovea centralis (which corresponds to the clinical macula) is a depression or pit in the neural retina that is approximately the same size, especially in horizontal measure, as the corresponding optic disc (i.e., 1.5 mm).

3. The anatomic foveola (which corresponds to the clinical fovea) is a small (∼350 µm diameter) reddish disc—that is, the floor of the fovea; it is a major portion of the foveal avascular zone (l500 to 600 µm diameter).

4. The anatomic macula (which corresponds to the clinical posterior pole) comprises an area larger than the anatomic fovea.

a. The term macula is derived from the term macula lutea.

b. It is equated with the histologic appearance of more than a single layer of ganglion cells (i.e., area centralis).

c. The anatomic macula actually encompasses an area contained just within the optic nerve and the superior and inferior retinal temporal arcades, and extends temporally approximately two disc diameters beyond the central fovea.

1) The ganglion cell layer is a continuous, single-cell layer everywhere in the neural retina except in the macular region, where it thickens to form a multilayer.

2) The darkness of the central area of the anatomic macula as seen in fluorescein angiograms is caused by four factors: (1) the yellow pigment (xanthochrome) present mainly in the middle layers of the central macular retina; (2) the central avascular zone; (3) the taller, narrower RPE cells, which contain more melanin granules per unit than elsewhere; and (4) the increased concentration in the central macular RPE of lipofuscin, which acts as an orange filter in filtering out the fluorescence.

III. The retina is susceptible to many diseases of the central nervous system, as well as to diseases affecting tissues in general. In addition, the highly specialized photoreceptor cells are subject to their own particular disorders.

Congenital Anomalies

Albinism (Fig. 11.4)

Albinoidism is outlined in Box 11.1.

Box 11.1

Albinoidism

Oculocutaneous or ocular hypopigmentation without nystagmus and photophobia

B Hair-Bulb Test Negative

(Modified from Kinnear PE, Jay B, Witkop CJ Jr et al.: Albinism. Surv Ophthalmol 30:75, 1985.)

Grouped Pigmentation (Bear Tracks)

The histologic appearance of grouped pigmentation is almost identical to that of congenital hypertrophy of the RPE and probably represents a clinical variant (see Chapter 17).

Coloboma

I. The typical coloboma “of the choroid” (see Fig. 9.8) involves the region of the embryonic cleft (fetal fissure; i.e., inferonasally) and is bilateral in 60% of patients. The coloboma may involve the total region, a large part of it, or one or more small isolated parts.

II. Histologically, the RPE seems to be primarily involved and is absent in the area of the coloboma.

A. The neural retina is atrophic and gliotic and may contain rosettes.

B. The choroid is partially or completely absent, and the RPE is usually hyperplastic at the edge of the coloboma.

The sclera may be thinned or even absent in the area of the coloboma, and the neural retina may herniate through in the form of a cyst (microphthalmos with cyst), undergo massive glial proliferation (massive gliosis), or both (see Chapter 14).

Retinal Dysplasia

See Chapter 18.

Lange’s Fold

The consistent axial and forward direction of Lange’s fold may be related to the vitreous base–zonular adhesion to the inner neural retinal surface that, in infants, seems to be stronger than the peripheral neural retina–RPE adhesion.

Congenital Nonattachment of the Retina

The space between the neural retina and the RPE closes progressively during fetal life. If something should happen shortly before birth to reverse this trend and rapidly separate the two layers, a congenital neural retinal detachment, secondary in nature, would result. A retinal dialysis (disinsertion), usually located inferotemporally, may develop in utero and lead to a secondary congenital or developmental neural retinal detachment.

Neural Retinal Cysts

I. A cyst of the neural retina (see Fig. 11.56) is defined arbitrarily as an intraneural retinal space whose internal–external diameter is greater than the thickness of the surrounding neural retina and of approximately equal dimension in any direction.

Retinoschisis, on the other hand, is an intraneural retinal space whose internal–external diameter is smaller than the thickness of the surrounding neural retina and much smaller than the width of the space lying parallel to the neural retina. Cyst is a poor term because a cyst, by definition, is an epithelium-lined space. However, the term (e.g., intraretinal, intracorneal, intrascleral) is frequently used to describe an intratissue space not necessarily lined by epithelium.

II. Congenital neural retinal cysts have been reported in the periphery, usually the inferior temporal region, and in the macula.

III. Histologically, the cysts are usually lined by gliotic neural retina and are filled with material that is periodic acid–Schiff (PAS)-positive but negative for acid mucopolysaccharides.

Myelinated (Medullated) Nerve Fibers

I. Myelinated nerve fibers (MNF; Fig. 11.6) usually occur as a unilateral condition, somewhat more common in men than in women.

A. They are seen in approximately 0.5% of eyes. MNF usually appear at birth or in early infancy and then remain stationary.

B. Rarely, MNF occur after infancy and can progress.

II. Clinically, they appear as an opaque white patch or arcuate band with feathery edges.

The area of myelination clinically is most commonly found continuous with the optic disc, but it may be seen in other parts of the neural retina. In autopsy studies, however, only approximately one-third of cases show myelination continuous with the optic nerve; perhaps myelination of the neural retina away from the optic nerve is overlooked clinically. Rarely, the condition may be inherited. The area of myelination may become involved in multiple sclerosis.

III. Histologically, myelin (and possibly oligodendrocytes) is present in the neural retinal nerve fiber layer, but the region of the lamina cribrosa is free of myelination.

Leber’s Congenital Amaurosis

I. Leber’s congenital amaurosis (LCA) is a heterogeneous group of infantile tapetoretinal degenerations characterized by connatal blindness, nystagmus, and a markedly reduced or absent response on the electroretinogram (ERG).

The differential diagnosis of connatal blindness includes hereditary optic atrophy, congenital optic atrophy, retarded myelinization of the optic nerve, albinism, aniridia, congenital cataracts, macular “coloboma,” and achromatopsia. Only Leber’s congenital amaurosis, however, shows an absent or markedly diminished response on ERG. At least 18 LCA genes have been reported with the most common mutated genes CEP290 and GUCY2D.

II. An autosomal-recessive inheritance pattern predominates, although a few cases of dominant transmission have been reported.

Senior–Loken syndrome is an autosomal recessive oculorenal condition, characterized by nephronophthisis and early childhood-onset of LCA. It is associated with mutations in five of the NPHP genes. Variations in some genes (e.g., NPHP5 and NPHP6) can cause different phenotypes in different individuals.

III. The fundus shows a polymorphous picture, including a normal appearance, arteriolar narrowing, optic pallor, granular or salt-and-pepper appearance or bone spicule pigmentation (especially with increasing age), diffuse white spots, a nummular pigmentary pattern, and a local or diffuse chorioretinal atrophy with various pigmentary changes.

A variety of associated ocular findings include ptosis, keratoconus, strabismus, cataract, macular colobomas, and a “bull’s-eye” maculopathy. Systemic associations include mental retardation, hydrocephalus, and the Saldino–Mainzer syndrome (familial nephronophthisis and cone-shaped epiphyses of the hands).

IV. A low incidence of associated neurologic disease occurs, such as a form of psychomotor retardation and electroencephalographic abnormalities.

V. Histologically, the neural retina appears normal, completely disorganized, or anything in between. In early cases, outer segments of the rods and cones are missing, the cones form a monolayer of cell bodies, and the rods tend to cluster in the periphery and sprout neuritis.

Vascular Diseases

Definitions

Clinically, the largest retinal vessels are known by common usage as arteries and veins (rather than arterioles and venules). These terms are carried over into ophthalmic pathology.

Retinal Ischemia

Causes

I. Choroidal vascular insufficiency

A. Choroidal tumors such as nevus, malignant melanoma, hemangioma, and metastatic carcinoma may “compete” with the outer layers of the neural retina for nourishment from the choriocapillaris.

B. Choroidal thrombosis caused by idiopathic thrombotic thrombocytopenic purpura, malignant hypertension, collagen diseases, or emboli may occlude the choriocapillaris primarily or secondarily through effects on the choroidal arterioles. Rarely, large areas of choriocapillaris may be occluded chronically by such materials as accumulating amyloid, with surprisingly good preservation of the overlying neural retina.

II. Retinal vascular insufficiency

A. Large-artery disease anywhere from aortic arch to central retinal artery

1. Atherosclerosis shows patchy subendothelial lipid deposits and erosion of media.

a. The ocular manifestations of the aortic arch syndrome are similar to those seen in carotid artery occlusive disease, except that the aortic arch syndrome causes bilateral ocular involvement that tends to be severe.

b. Embolic manifestations (Figs. 11.7 and 11.8; see also Fig. 5.54)

Amaurosis fugax is a common symptom. Preceding this symptom, Hollenhorst plaques (cholesterol emboli), less commonly, platelet–fibrin emboli, and, rarely, atrial myxoma emboli may be observed in retinal arterioles.

1) Emboli are the most common cause of central retinal artery occlusion (CRAO) and originate in ulcerous plaques or thrombosis of mainly the internal carotid arteries. The emboli consist of cholesterol (Hollenhorst plaque), fibrinous, or calcific plaque materials.

2) Emboli (e.g., cholesterol, platelet–fibrin emboli, atrial myxoma, talc in drug abusers) to the visual system can cause amaurosis fugax; visual field defects; cranial nerve palsies; central or branch retinal artery occlusion; hypotensive retinopathy (venous stasis retinopathy) and the ocular ischemic syndrome (see later); narrowed retinal arterioles; and neovascularization of the iris, optic disc, or neural retina.

3) Rarely, ocular emboli cause a condition masquerading as temporal (cranial; giant cell) arteritis.

2. Takayasu’s disease usually occurs in young women (frequently Japanese), shows an adventitial giant cell reaction, also involves the media, and produces intimal proliferation with obliteration of the lumen.

Takayasu’s syndrome (aortic arch syndrome) occurs in older patients of either sex and differs from the “usual” type of atherosclerosis only in its site of predilection for the aortic arch. Another cause is syphilitic aortitis.

3. CRAO has many causes, including atherosclerosis, emboli, temporal arteritis, collagen diseases, homocystinuria, and Fabry’s disease. Broadly, CRAO can be divided into four types: (1) nonarteritic (NA-CRAO), (2) NA-CRAO with cilioretinal artery sparing, (3) transient NA-CRAO, and (4) arteritic CRAO.

Rarely, bilateral CRAO may occur. It usually involves elderly patients. The annualized incidence for white patients is approximately 1.9% per 100,000.

4. Collagen diseases, allergic granulomatosis, and midline lethal granuloma syndrome may all involve the larger retinal vessels, causing neural retinal ischemia.

5. Temporal (cranial; giant cell) arteritis (see Chapter 13)

B. Arteriolar and capillary disease of neural retinal vasculature

1. Arteriolosclerosis is associated with hypertension.

2. Branch retinal artery occlusion has many causes, including emboli (see Figs. 11.7 and 11.8), arteriolosclerosis, diabetes mellitus, arteritis, dysproteinemias, collagen diseases, and malignant hypertension.

Susac’s syndrome consists of the triad of encephalopathy, branch retinal artery occlusion, and hearing loss, most common in women. The cause is uncertain, but it is thought to be an autoimmune disease.

3. Diabetes mellitus (see Chapter 15)

4. Malignant hypertension, toxemia of pregnancy, hemoglobinopathies, collagen diseases (Fig. 11.9), dysproteinemias, carbon monoxide poisoning, and blood dyscrasias of many kinds may involve the small retinal vessels and cause neural retinal ischemia.

Leukemic retinopathy commonly occurs in both acute and chronic leukemia. The findings include venous tortuosity and dilatation, perivascular sheathing, retinal hemorrhages (including white-centered hemorrhages, simulating Roth’s spots), leukemic infiltrates, cotton-wool spots, optic nerve infiltration, peripheral neural retinal microaneurysm formation, extensive capillary dropout, and even a proliferative retinopathy similar to sickle-cell retinopathy.

Histology of Retinal Ischemia

I. Early (Fig. 11.10; see also Figs. 11.9 and 11.15D)

A. The neural retina shows coagulative necrosis of its inner layers, which are supplied by the retinal arterioles.

1. The neuronal cells become edematous during the first few hours after occlusion of the artery.

2. The intracellular swelling accounts for the clinical gray neural retinal opacity.

B. If the area of coagulative necrosis (see Chapter 1) is small and localized, it appears clinically as a cotton-wool spot.

1. The cotton-wool spot observed clinically (Fig. 11.11; see also Fig. 11.9) is a result of a microinfarct of the nerve fiber layer of the neural retina.

2. The cytoid body, observed microscopically (see Figs. 11.9 and 11.11), is a swollen, interrupted axon in the neural retinal nerve fiber layer.

Histologically, the swollen end-bulb superficially resembles a cell, hence the term cytoid body. A collection of many cytoid bodies, along with localized edema, marks the area of the microinfarct. A cotton-wool spot represents a localized accumulation of axoplasmic debris in the neural retinal nerve fiber layer. They result from interruption of orthograde or retrograde organelle transport in ganglion cell axons (i.e., obstruction of axoplasmic flow). Ischemia is the most common cause of focal interruption of axonal flow in the neural retinal nerve fiber layer that results in a cotton-wool spot. However, any factor that causes focal interruption of axonal flow gives rise to similar accumulations.

C. If the area of coagulative necrosis is extensive, it appears clinically as a gray neural retinal area, blotting out the background choroidal pattern.

The clinically seen gray area is caused by marked edema of the inner half of the neural retina. It is noted several hours after arterial obstruction and becomes maximal within 24 hours. With complete coagulative necrosis of the posterior pole (e.g., after a central retinal artery occlusion), the red choroid shows through the central fovea as a cherry-red spot. The foveal retina has no inner layers and is supplied from the choriocapillaris; therefore, no edema or necrosis occurs in the central fovea and the underlying red choroid is seen.

II. Late (see Fig. 11.10)

A. The outer half of the neural retina is well preserved.

B. The inner half of the neural retina becomes “homogenized” into a diffuse, relatively acellular zone. Usually, thick-walled retinal blood vessels are present.

Because the glial cells die along with the other neural retinal elements, gliosis does not occur. The boundaries between the different retinal layers in the inner half of the neural retina become obliterated. In central retinal artery occlusion, the inner neural retinal layers become an indistinguishable homogenized zone. In retinal atrophy secondary to glaucoma, to transection of the optic nerve, or to descending optic atrophy, however, the neural retinal layers, although atrophic, are usually identifiable.

Retinal Hemorrhagic Infarction (Fig. 11.12)

Causes and Risk Factors of Hemorrhagic Infarction

I. The many causes (or associations) include chronic primary open-angle glaucoma, atherosclerosis of the central retinal artery, arteriolosclerosis of the retinal arterioles, systemic hypertension, diabetes mellitus, polycythemia vera, mediastinal syndrome with increased venous pressure, dysproteinemias, and collagen diseases.

Arterial vascular disease is commonly present in retinal vein occlusion and is probably related to its cause. Also, CRVO may occur in Reye’s syndrome (encephalopathy and fatty degeneration of viscera), which has a typical diphasic course, with a mild viral illness followed by severe encephalitic symptoms, especially coma. Other risk factors for retinal vein occlusion include black race, male sex, hypertension, end-organ damage in diabetics, and obstructive sleep apnea.

II. Significant risk factors are systemic hypertension, open-angle glaucoma, and male sex. Race, diabetes mellitus, coronary artery disease, and stroke do not appear to be significant risk factors.

Types of Hemorrhagic Infarction

I. Occlusion of central retinal vein, branch retinal vein, or venule

A. CRVO may be considered to consist of two distinct types.

1. Nonischemic retinopathy (~65% of cases, but approximately one-fourth of these eyes will convert to the ischemic type)

a. The retinal arterial pressure in CRVO is normal or high, unlike the low arterial pressure found in ocular ischemic syndrome (OIS).

The term venous stasis retinopathy is also used for nonischemic retinopathy, but it is more appropriately used for the retinopathy of OIS (see earlier).

b. The condition is probably caused by a reversible, complete occlusion of the central retinal vein, usually behind the lamina cribrosa in the substance of the optic nerve or where the vein enters the subarachnoid space, and is not accompanied by significant hypoxia.

c. Retinal hemorrhages vary from a few, flame-shaped and punctate, to large numbers. Those in the peripheral neural retina tend to be punctate and more numerous than those in the center. Cotton-wool spots are absent or sparse.

d. Retinal capillary perfusion is usually normal so that the choroidal background is easily seen. Dilated and leaking retinal capillaries may be seen with fluorescein angiography.

e. Two subgroups may be identified: One subgroup involves young people in whom some evidence suggests that the condition is probably inflammatory in origin, caused by phlebitis of the central retinal vein that produces venous thrombosis (see discussion of papillophlebitis, later in this subsection); a second subgroup involves older people who have arteriosclerosis, which probably plays an important role in the venous occlusion.

The second subgroup may consist of two types: One (sometimes called incomplete occlusion) shows normal retinal arterial circulation and normal or slightly slowed retinal venous circulation; the other (sometimes called venous stasis retinopathy) shows slow retinal arterial and venous circulation. Both show normal capillary perfusion.

2. Ischemic (hemorrhagic) retinopathy

a. It is caused by occlusion of the central retinal vein at, or anterior to, the lamina cribrosa, associated with retinal ischemia that leads to significant retinal hypoxia.

1) Few venous collateral channels are available to the central retinal vein at, or anterior to, the lamina cribrosa; therefore, severe obstruction of retinal venous flow results.

2) Approximately 35% of cases fall into the ischemic group. If untreated iris neovascularization occurs in most eyes that have ischemic CRVO.

b. Neural retinal hemorrhages are usually gross and extensive (“blood and thunder” fundus). Cotton-wool spots and retinal capillary nonperfusion are prominent, resulting in partial or complete obscuration of the underlying choroidal pattern. The optic nerve head is usually edematous.

Extensive retinal capillary closure one month after vein occlusion (central or branch) or extensive leakage and a broken capillary arcade at the fovea, as determined by fluorescein angiography, indicates a poor visual prognosis. When neovascularization of the neural retina or iris develops, it is invariably in those patients who have extensive retinal capillary closure.

3. CRVO occur in 8–20% of patients who already have chronic primary open-angle glaucoma or in whom it will develop.

In at least 80% of eyes that have CRVO uncomplicated by neovascularization of the iris, the intraocular pressure is lower in the eye with the occlusion than in the normal fellow eye. The reduction of intraocular pressure is greater (1) in those eyes with CRVO than in those with branch-vein occlusion, (2) in those eyes with ischemic retinopathy than in those with nonischemic retinopathy, and (3) in patients who have high pressures in their fellow eyes. The pressure reductions persist for at least two years after occlusion.

4. Bilateral CRVO may occur as part of the acquired immunodeficiency syndrome (AIDS).

B. Branch retinal vein occlusion (BRVO)

1. BRVO occurs approximately three times more frequently than CRVO. In approximately two-thirds of cases, the superior temporal neural retinal vein is involved. Most of the remaining cases show involvement of the inferior temporal retinal vein.

a. Rarely, the inferior (or superior) branch of the central retinal vein may be involved, resulting in an inferior (or superior) hemispheric vein occlusion.

b. A hemispheric vein occlusion behaves like an ischemic CRVO.

c. Retinal vascularity is strongly correlated with vitreous fluid levels of sVEGFR-2, VEGF, slCAM-1, IL-6, PTX3, and PEDF.

2. The occlusion most often occurs in the fifth or sixth decade of life and develops at an arteriovenous crossing.

3. If significant and widespread retinal capillary nonperfusion is present, neovascularization of the optic nerve head, neural retina, or both develops in a high percentage of cases. Iris neovascularization does not occur.

It is important to differentiate retinal venous collaterals from neovascular areas. The former prove to be beneficial, whereas the latter may require therapy.

4. Visual acuity may be decreased because of cystoid macular edema (~50% of cases) or foveal hemorrhage. After BRVO, significant improvement in vision beyond 20/40 is uncommon.

II. Papillophlebitis (retinal vasculitis, mild and moderate papillary vasculitis, benign retinal vasculitis, optic disc vasculitis)

A. Papillophlebitis is characterized by a unilateral, partial, reversible CRVO presumably caused by venous inflammation. It usually occurs in young, healthy men and exhibits a benign, somewhat protracted course.

B. Ophthalmoscopic findings include edema of the optic nerve head, peripapillary neural retina, and sometimes macula; retinal venous dilatation and tortuosity; and scattered, superficial, mid-peripheral retinal hemorrhages.

C. The prognosis for vision is excellent.

The main sequelae are perivenous sheathing of large veins at the posterior pole and dilated venules over the optic nerve head.

III. Terson’s syndrome (see Chapter 12)

Complications of Hemorrhagic Infarction

I. Macular hemorrhagic infarction may result in permanent loss of vision.

II. Leakage of fluid into the macula may result in cystoid macular edema.

III. Iris neovascularization (clinically seen rubeosis iridis)

A. Iris neovascularization (see Figs. 9.13 and 9.14) occurs mainly with ischemic CRVO; it rarely occurs with nonischemic CRVO or BRVO.

B. Approximately 60% of patients older than 40 years of age have iris neovascularization after ischemic CRVO (rarely after nonischemic CRVO). Iris neovascularization usually does not appear before six weeks after occlusion, usually becomes established before six months, and, if untreated, causes neovascular glaucoma.

Early, the anterior chamber angle may show neovascularization for 360° and yet still be open and cause secondary open-angle glaucoma. This stage tends to be fleeting, peripheral anterior synechiae develop, and secondary closed-angle glaucoma ensues. The glaucoma is called neovascular glaucoma. Iris neovascularization is rare in people who are younger than 40 years of age at the time of their CRVO.

IV. Neovascularization of the neural retina (Fig. 11.13) occurs mainly with BRVO; it rarely occurs with ischemic or nonischemic CRVO.

V. Neural retinal detachment secondary to branch retinal vein occlusion may occur when the vein occlusion is severe and accompanied by marked capillary nonperfusion and leakage.

VI. Optociliary shunt vessels (i.e., usually large veins connecting the choroidal and retinal circulations at the optic nerve head) may develop after CRVO.

Optociliary shunt vessels are mainly seen in three clinical situations: as congenital anomalies; as the result of CRVO; and in association with orbital tumors, especially optic nerve sheath meningiomas. The vessels may also be seen in optic nerve juvenile pilocytic astrocytomas (gliomas), arachnoid cysts, optic nerve colobomas and drusen, and with chronic atrophic optic disc edema.

VII. Exudative neural retinal detachment

Hypertensive and Arteriolosclerotic Retinopathy1

I. Hypertensive retinopathy (Fig. 11.14)

A. Grade I: a generalized narrowing of the arterioles

B. Grade II: grade I changes plus focal arteriolar spasms

C. Grade III: grade II changes plus hemorrhages and exudates

1. Flame-shaped (splinter) hemorrhages (see Figs. 11.12–11.14; see also Fig. 15.18) are characteristic and present in the nerve fiber layer.

2. Dot-and-blot hemorrhages (see Figs. 11.13 and 15.18) may be seen in the inner nuclear layer with spreading to the outer plexiform layer.

3. Cotton-wool spots (see Figs. 11.11 and 11.14; see earlier in this chapter) are characteristic.

Cotton-wool spots may be seen in many conditions, such as collagen diseases, CRVO, blood dyscrasias, AIDS, and multiple myeloma.

4. Hard (waxy) exudates may be seen; these are lipophilic exudates located in the outer plexiform layer (see Figs. 11.14, 15.13, and 15.16).

When the exudates are numerous in the macula and lie in the obliquely oriented and radially arranged fiber layer of Henle, they appear as a macular star.

D. Grade IV: all the changes of grade III plus optic disc edema

Necrosis, thinning, clumping, and proliferation of the RPE may occur as a result of obliterative changes in the choriocapillaris in malignant hypertension. Four types of fundus lesions associated with choroidal vascular changes have been recognized clinically: (1) pale yellow or red patches bordered to a varying extent by pigment deposits; (2) black, isolated spots of pigment with a surrounding yellow or red halo caused by complete obstruction of terminal choroidal arterioles and choriocapillaris by fibrin thrombi (Elschnig’s spots; see Fig. 11.14D); (3) linear chains of pigment flecks along the course of a yellow-white sclerosed choroidal vessel (Siegrist’s spots); and (4) yellow or red patches of chorioretinal atrophy.

II. Arteriolosclerotic retinopathy (Fig. 11.15)

A. Grade I: an increase in the arteriolar light reflex

Subintimal hyalin deposition and a thickened media and adventitia cause the normally transparent arteriolar wall to become semiopaque, producing an increased light reflex.

B. Grade II: grade I changes plus arteriolovenular crossing defects

The semiopaque wall of the arteriolosclerotic arteriole, which shares a common adventitia with the venule where they cross, obscures the view of the underlying venule. This results in the clinically seen arteriolovenular crossing defects, or “nicking.”

C. Grade III: grade II changes plus “copper-wire” arterioles

The arteriolar wall becomes sufficiently opaque so that the blood column can only be seen by looking perpendicularly through the surface of the wall (i.e., looking through the thinnest area). The arteriole has a burnished or copper appearance due to reflection of light from the thickened and partially opacified wall.

D. Grade IV: grade II changes plus “silver-wire” arterioles

The wall becomes totally opaque so that the blood column in the lumen cannot be seen. The light is then reflected completely from the surface of the thickened vessel, giving a white or silver appearance. The lumen of the arteriole may or may not be patent. Patency can best be determined by fluorescein angiography.

Hemorrhagic Retinopathy

I. Neural retinal hemorrhages (see Figs. 11.12 and 15.18) may be caused by many diseases, such as diabetes mellitus (see Chapter 15), sickle-cell disease, retinal venous diseases, hypertension, blood dyscrasias, leukemias, polycythemia vera, subacute bacterial endocarditis, cytomegalovirus retinitis, acute retinal necrosis (ARN), lymphomas, idiopathic thrombocytopenia, trauma, multiple myeloma, pernicious anemia, collagen diseases, carcinomatosis, anemia, and many others.

Anemia or thrombocytopenia alone rarely causes neural retinal hemorrhages. Anemia and thrombocytopenia combined, however, not infrequently result in neural retinal hemorrhages; when the two are severe (hemoglobin <8 g/100 ml and platelets <100,000/mm), neural retinal hemorrhages may occur in 70% of patients.

II. Histologically, the size and anatomic location of the hemorrhage determine its clinical appearance (see Fig. 15.18).

III. Roth’s spots

A. Roth’s spots are a special type of neural retinal hemorrhage characterized by a white center and associated with bacterial endocarditis.

It was Litten who described the association (Litten’s sign) and referred to it as Roth’s spots.

B. The white spots probably represent capillary rupture, extravasation, and formation of a central fibrin–platelet plug rather than septic microabscesses.

Diabetes Mellitus

See Chapter 15.

Coats’ Disease, Leber’s Miliary Aneurysms, and Retinal Telangiectasia

See Chapter 18.

Idiopathic Macular Telangiectasia (Idiopathic Juxtafoveolar Retinal Telangiectasis)

See Chapter 18.

Retinal Arterial and Arteriolar Macroaneurysms

I. Macroaneurysms of the retinal arteries and arterioles (Fig. 11.16) may be congenital or acquired.

A.

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