(WEB: The Eyes have it)

Normal Optic Disc

The optic disc is shaped like a doughnut with a pink neuroretinal rim and a central white

depression called the physiologic cup.

Check out the color of the neuroretinal rim, which carries the axons of the retinal ganglion

cells. It should be orange-pink. If its axons die, the rim will turn white. Inflammation,

infarction, and compression are common causes.

Inspect the external margins of the neuroretinal rim. Are they distinct? Some fuzziness of

the nasal margin is acceptable. Otherwise, the optic nerve may be pathologically swollen,

particularly if the rim rises well above the retinal surface. Common causes of disc edema are

increased intracranial pressure and optic nerve inflammation and infarction.

Inspect the physiologic cup. Its horizontal diameter should not exceed 1/2 the horizontal

diameter of the entire disc (the "cup-to-disc ratio"). Otherwise, suspect pathologic optic disc

cupping. Glaucoma is the commonest cause.

Arteries and Veins of the Normal Optic Fundus

The retinal arteries and veins emerge from the nasal side (left) of the optic disc. Vessels

directed temporally have an arching course; those directed nasally have a radial course.

Arteries are brighter red and narrower than veins. Actually, the retinal arteries lack a

muscular coat, so they are more correctly called arterioles. The vessels you see here supply

and drain the inner retina, including the retinal ganglion cells and their axons and the

bipolar cells. The outer retina, including the rods and cones and retinal pigment epithelium,

is supplied by the choroidal circulation.

The fovea is a 2.5 mm-diameter area that looks slightly darker than the surrounding retina

because of increased pigment. It is centered about 2 1/2 disc diameters temporal to the

optic disc. The fovea lies in the center of the macular region.

Made up exclusively of cones, the fovea processes high-contrast discriminative vision (visual

acuity) and color vision. Without it, you could not see fine detail. The most common disorder

of the macular region in the elderly is age-related macular degeneration, an idiopathic

disorder of the retinal pigment epithelium. Other important macular disorders are diabetic

macular edema, toxoplasmosis, and cherry-red spot.

Pathologic Optic Disc Cupping

In this eye, the disc neuroretinal rim is much thinner than in the normal optic disc. The cup-to-disc ratio here is about 0.8—much greater than the physiologic limit of 0.5! When the cup-to-disc ratio exceeds 0.5, optic disc cupping is probably pathologic. This patient has glaucoma. To find out more about glaucoma, click here.

Optic Disc Pallor

In this eye, the neuroretinal rim is much whiter than in the normal optic disc. The pallor

reflects replacement of dead axons by glial tissue. The loss of the small capillaries within the

nerve accounts for the shift from orange-pink to white.

Be careful about judging optic nerve function by its color. First, the color change may be

very subtle. Second, it takes many weeks of optic nerve damage before pallor appears.

Third, a cataract may make a pale disc look orange.

Congenital Optic Disc Anomaly

In this eye, the optic disc is pathologically elevated above the retinal surface. It lacks a

physiologic cup, and its margins are slightly blurred. The signs depicted here are caused by

a congenital optic disc anomaly, leading to overcrowding of axons as they exit the eye.

It is often difficult to tell the difference between a congenital optic disc anomaly and optic

disc edema, an acquired swelling of optic nerve axons caused by increased intracranial

pressure, infarction, or inflammation of the optic nerve.

Acute Optic Disc Edema

The optic disc is elevated and its surface is covered by cotton wool spots and flame

hemorrhages. The cotton wool spots reflect explosion of damaged axons; the flame

hemorrhages reflect explosion of vessels under pressure.

Although blurred optic disc margins and disc elevation can also be caused by a congenital

optic disc anomaly, the cotton wool spots and hemorrhages tell you the disorder is acquired.

Optic disc edema is commonly caused by the four "I's":

increased intracranial pressure (papilledema)

infarction

inflammation

infiltration (by cancer)

Compression and toxins are other causes. You cannot differentiate one cause of optic disc

edema from another on the basis of its ophthalmoscopic appearance! You must use non-

ophthalmoscopic information, such as visual acuity or visual field defect, to make that

distinction.

Subtle Optic Disc Edema

This is an example of subtle optic disc edema. The temporal margin appears quite distinct,

but the nasal, superior, and inferior margins are not. Blurred nasal margins are acceptable in

the normal optic disc, but its upper and lower poles should have discrete borders.

Chronic Optic Disc Edema

This optic disc is elevated and its surface is turning white. The edema tells us that

axoplasmic flow is backed up in some axons. The pallor tells us that other axons have died—

from the effects of axoplasmic stasis!

Patients with this sign have constricted visual fields. The usual cause is chronic elevated

intracranial pressure. At this stage, vision may not improve even if the pressure is relieved

and the optic disc edema disappears. The disc will then be flat but pale.

Arteriovenous Nicking

Chronic hypertension has stiffened the arteries. At arteriovenous crossing points, they

indent and displace the more pliant veins. Called arteriovenous nicking, this phenomenon

does not occur in the normal fundus.

Increased Light Reflection in Chronic Hypertension

Chronic hypertension also thickens the arterioles. Intimal and subintimal fibrosis

narrows their lumina, and gives the red reflection from their blood columns a

shiny appearance (increased light reflection). At first, the light reflection has a

bronze sheen ("copper-wiring"); with continued hypertension, it develops a

whitish glint ("silver-wiring").

Obliterative Retinal Vasculopathy

The white, string-like vessel has been completely occluded by an old thrombus.

Longstanding occlusion of arterioles gives them a thready, white appearance, like a pipe

cleaner.

This patient, who has lupus erythematosus, has visual field loss corresponding to the area of

infarcted retina around this obliterated arteriole.

Hollenhorst Plaque

The yellow fleck trapped at the bifurcation of retinal arterioles is probably a platelet-fibrin-

cholesterol embolus. Called a Hollenhorst plaque, it originated in an atheroma of the cervical

carotid bifurcation.

Most retinal emboli arrive at their stopping points without infarcting the retina, as shown

here. But if they plug an important proximal feeder vessel, they may cause a segmental

retinal infarct and a disturbing visual field defect.

Segmental Retinal Infarct from Embolus

This refractile, yellow fleck is a platelet-fibrin-cholesterol retinal embolus called a

Hollenhorst plaque. It has lodged at a critical bifurcation near the fovea and

caused a moderate-sized branch retinal artery occlusion and a segmental retinal

infarct. The patient would report an area of cloudy vision just above fixation.

Calcific Intraluminal Plaque

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This white fleck is a calcific embolus that came from the aortic valve. Somehow it did not

cause a retinal infarct!

Retinal Vasculitis

The white cuff that looks like frosting along the vessels is a perivenous lymphocytic

infiltration. Sometimes called "sheathing," it betokens a vasculitis.

Retinal vasculitis occurs in sarcoidosis, Behçet's Disease, multiple sclerosis, and in idiopathic

conditions. But contrary to popular opinion, it is extremely rare in connective tissue

disorders such as lupus. Instead, connective tissue diseases produce multiple bland

occlusions appearing as cotton wool spots, branch retinal artery occlusions, and obliterative

vasculopathy.

Myelinated Nerve Fibers

The white clouds that surround the optic disc represent a congenital anomaly called

myelinated retinal nerve fibers. Myelination does not normally extend onto the retina. When

it does, these clouds appear permanently adjacent to the optic disc. They do not interfere

with vision.

Did you mistake these myelinated nerve fibers for cotton wool spots or retinal infiltrates?

Many people do. They are whiter, larger and denser than cotton wool spots and are almost

always connected to the optic disc. They are unlike retinal infiltrates in having no overlying

vitreous haze.

To review the many other yellow-white things in the retina with which you could confuse

myelinated nerve fibers, check out Yellow-White Things in the Retina.

Cotton Wool Spots

These yellow-white spots are called cotton wool spots. They are caused by retinal nerve fiber

layer microinfarcts. Exploded retinal ganglion cell axons extrude their axoplasm like

toothpaste. Expect to find cotton wool spots arrayed around the optic disc and along the

temporal vascular arcades.

Cotton wool spots have a myriad of causes. Any process that occludes small retinal

arterioles will do this: hypertension, diabetes, HIV, severe anemia or thrombocytopenia,

hypercoagulable states, connective tissue disorders, viruses, lues, Behçet's and many

others.

To review the many other yellow-white things in the retina with which you could confuse

cotton wool spots, check out Yellow-White Things in the Retina.

Roth Spot

The Roth Spot is a white-centered hemorrhage. Actually, it is a cotton wool spot surrounded

by hemorrhage. The cotton wool comes from ischemic bursting of axons; the small

hemorrhage comes from ischemic bursting of a pre-capillary arteriole. Many, many

conditions may cause this. It is not, as often supposed, specific to bacterial endocarditis!

Hard Exudates

These yellow flecks are called hard exudates. They are the lipid residues of serous leakage

from damaged capillaries. The commonest cause is diabetes. Other causes are retinal vein

occlusion, angiomas (Von Hippel-Lindau Disease), other vascular dysplasias, and radiation-

induced retinal vasculopathy.

If you think you could confuse hard exudates with other yellow-white things in the retina

(yes, easily), check out Yellow-White Things in the Retina.

Retinal Drusen

The yellow-white flecks scattered around the macular region are little mounds beneath the

retinal pigment epithelium. They are tombstones of dead retinal pigment epithelial cells. The

commonest cause is age-related macular degeneration, a common but poorly understood

disorder of the elderly.

At this stage, visual acuity may be only slightly abnormal. If the retinal pigment epithelium

dies further, vision will fail as the foveal region turns into a confluent yellow-white area. The

greatest threat to vision, however, is the development of submacular neovascularization,

which can cause bleeding in the retina.

Retinal Infiltrate

The yellow-white area with fuzzy edges is a retinal infiltrate. It consists of inflammatory cells,

dead retinal tissue, and perhaps micro-organisms. Its indistinct margins and overlying

vitreous haze distinguish it from other yellow-white things in the retina.

This patient has retinal toxoplasmosis. In immunocompromised hosts, such as this patient

with HIV disease, the toxoplasmosis is usually acquired, and no old scars are seen. In

immunocompentent hosts, this condition usually represents satellite reactivation of a

congenital lesion, evident as an adjacent healed chorioretinal scar.

Dot, Flame, Boat Retinal Hemorrhages

This slide of a patient with acute lymphocytic leukemia shows three types of retinal

hemorrhages.

The dot hemorrhages, lying deep within the retina, reflect leakage of capillaries or venules.

They are common in diabetes.

The flame hemorrhages, lying within the superficial nerve fiber layer, reflect ischemic

leakage from arterioles or veins that are ischemic or, in the case of veins, under high

pressure.

The boat hemorrhage (pre-retinal), lying at the interface between retina and vitreous,

reflects leakage under enough pressure to burst through the internal liminiting membrane of

the retina.

Blood can also escape into the vitreous cavity to cause a vitreous hemorrhage.

To learn more about retinal hemorrhages and their causes, check out Retinal Hemorrhages.

Submacular Hemorrhage

This patient has developed bleeding in the macula. The cause of the bleeding is choroidal

neovascularization, that is, a net of new blood vessels that have burrowed from the choroid

under the retina.

The gray portion lies under the retinal pigment epithelium. Surrounding the gray

hemorrhage is a ring of red blood that has escaped into the retina. This patient has age-

related macular degeneration, the commonest cause of choroidal neovascularization and

submacular hemorrhage.

To learn more about retinal hemorrhages and their causes, check out Retinal Hemorrhages.

Retinal Neovascularization

This tangle of blood vessels on the retinal surface is a crude attempt at vascularizing

ischemic tissue. Retinal neovascularization lacks the bifurcating pattern of normal vessels.

Poorly and hastily built, they bleed spontaneously or with minimal trauma. The blood pours

into the retina and into the interface between retina and vitreous, where it attracts fibroglial

elements which form fibrovascular stalks. The stalks induce vitreous contraction which pulls

them farther away from the retina. Eventually the retina detaches. The combination of

hemorrhage and retinal detachment spells blindness.

The common causes of retinal neovascularization on or near the optic disc are diabetes,

retinal vein occlusion, and radiation. Neovascularization in the peripheral retina (out of view

of the direct ophthalmoscope) is most commonly caused by sickle cell disease and

retinopathy of prematurity.

Retinal Pigment Epitheliopathy

Diffuse damage to the retinal pigment epithelium (RPE), which anchors the photoreceptors,

occurs in many hereditary, intra-uterine inflammatory, and acquired toxic-metabolic

disorders. Two retinal areas are most vulnerable: the mid-peripheral (equatorial) and the

perifoveal regions.

Notice that the retinal arterioles are very thin compared to those of the normal fundus. This

arteriolar narrowing is particularly common in advanced hereditary disorders of the RPE.

Damage to the RPE causes the RPE to migrate into the superficial retina. The black pigment

flecks are particularly evident in the retinal mid-periphery.

The combination of RPE loss and migration produces the "salt and pepper" fundus. The

pepper may be clumpy ("bone spicular"), as in the hereditary degenerations, or very fine, as

in the intra-uterine inflammations like rubella. Depending on the degree of damage, the

patient with peripheral retinal pigment epitheliopathy may be asymptomatic or have

profound loss of night vision and construction of the visual field.

In the perifoveal region, you will sometimes see a grayish-brown halo that looks like a bull's

eye. Patients may notice blurred vision just off center. Eventually the foveal region itself

becomes damaged and visual acuity falls.