Ординатура / Офтальмология / Английские материалы / Manual for Eye Examination and Diagnosis_Leitman_2007
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Another disk variation occurs when the myelin sheath that normally covers the optic nerve extends onto the retina, appearing like white flame-shaped patches obscuring the disk margin. It is benign (Fig. 301). The disk margin may also be obscured by drusen (Fig. 302) which are small, round, translucent bodies. They may damage nerve fibers and cause an enlarged blind spot.
Fig. 301 Myelination of the optic nerve.
The choroid
The choroid is highly vascularized and nourishes the rod and cone layer and the retinal pigment epithelium. Unlike the tree-like branching of the retinal vessels, the choroidal circulation forms a criss-crossing network. As the retinal pigment epithelium loses pigment with age, the choroidal vasculaturè becomes more visible, resulting in a tigroid appearance (see Fig. 298).
Fundus examination
The fundus refers to the inner part of the eye
seen with ophthalmoscopy, that is, the retina,
choroid, and disk. It is evaluated by first focus- Fig. 302 Disk drusen. ing on the optic disk and then on the retinal
blood vessels and surrounding retina. The macula is examined last to minimize miosis and discomfort.
A direct ophthalmoscope (Fig. 303) allows for monocular visualization of the posterior half
Fig. 303 Direct ophthalmoscope.
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Fig. 304 Indirect ophthalmoscope.
of the fundus, where most retinal pathology is located. Use a negative lens (red) for myopic eyes, and a plus lens (black) for hyperopic eyes. Get as close to the eye as possible and minimize movement by resting your hand that is holding the ophthalmoscope on the patient’s cheek.
A binocular indirect ophthalmoscope (Fig. 304) consists of a light source worn over the head and a hand-held lens, which allows the entire retina to be seen in three dimensions. Retinal holes and detachments at the ora serrata can be viewed by indenting the sclera with a small thimble worn on the index finger.
A three-mirror contact lens (Fig. 305) used with a slit lamp gives a stereoscopic detailed view of the entire retina. It is useful in studying subtle changes in each layer of the retina, and to gauge optic cupping. Its disadvantage is the need for anesthetic drops and a solution on the eye.
Fluorescein angiography
(Figs 306–308)
Fluorescein dye is injected intravenously. As it passes through the retinal circulation, fundus
Fig. 305 Three-mirror contact lens.
Fig. 306 Normal fluorescein angiogram.
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Fig. 307 Fluorescein angiogram of inferior retinal artery occlusion showing lack of perfusion inferiorly after 15.4 seconds.
photographs are made in a rapid sequence. This test is useful for evaluating retinal circulation. It demonstrates rate of flow, leakage from capillaries, staining of tissues, areas of nonperfusion, and neovascularization. Normally retinal blood vessels do not leak.
Papilledema (choked disk)
(Figs 308–311)
Papilledema is swelling of the optic disk, usually due to increased intracranial pressure, in which case it is eventually bilateral. Unilateral cases are due to increased pressure in one orbit, sometimes caused by a tumor. It begins with blurred disk margins and engorged disk veins. As it progresses, flame-shaped hemorrhages and cotton-wool spots develop in the peripapillary area (Fig. 309). Chronic, elevated intracranial pressure inevitably destroys the optic nerve, resulting in optic atrophy.
In 80% of normal eyes, there are subtle pulsations of the retinal veins as they exit from the globe at the optic cup. If pulsations are not visible they can almost always be elicited by exerting slight pressure on the globe (through the lid). In papilledema, one cannot see spontaneous or elicited venous pul-
Fig. 308 Fluorescein angiogram of papilledema with leakage of dye from disk.
Fig. 309 Papilledema with elevated disk, engorged veins, and flameshaped hemorrhages.
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Fig. 310 An enlarged blind-spot can be plotted most accurately on a tangent screen.
sations. Swelling of the optic disk damages the surrounding retina and enlarges the blind spot, which helps confirm the diagnosis (Fig. 310). Elevated intracranial pressure that causes papilledema may also cause headache, nausea, and pressure on the CN VI, resulting in diplopia.
Differential diagnosis of papilledema
A swollen disk caused by optic neuritis (see Fig. 93) is associated with a Marcus Gunn pupil and loss of vision, whereas in papilledema the pupil is normal and there is usually no loss of visual acuity unless edema extends to the macula, sometimes resulting in a macular star (Fig. 311).
Early papilledema may be difficult to distinguish from drusen of the disk (Fig. 302) and myelinated nerve fibers (Fig. 301). All three blur the margin and cause an enlarged blind spot (Fig. 310). On fluorescein angiography, however, only papilledema has leakage of dye (Fig. 308). A hyperopic eye might have a small disk with blurred margin, but there is no leakage with fluorescein angiography. Like papilledema, central retinal vein occlusion (Fig. 321) may have venous engorgement, a blurred disk margin, and cotton-wool spots. In central retinal vein occlusion, however, the flame hemorrhages extend out to the periphery and there is usually more loss of vision. Malignant systemic hypertension can also cause a papilledema-like retinal appearance, which is easily distinguished by measuring blood pressure on all patients with blurred disk margins (Fig. 318).
Fig. 311 Papilledema with macular star (arrow).
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White retinal lesions
(Figs 312–316)
Cotton-wool spots (Fig. 312)
Ischemia of the superficial nerve fiber layer causes white, cloud-like lesions around the disk that obscure underlying retina. Causes include diabetes (Fig. 333), hypertension (Fig. 318), and papilledema. Up to 50% of AIDS patients may develop retinal microangiopathy with cotton-wool spots.
Inflammatory cells (Fig. 313)
White-blood cells occur in posterior choroiditis (Fig. 258), retinitis, vasculitis (Fig. 327), or optic neuritis. Often there is an unclear view because of overlying vitritis. Cytomegalovirus or necrotizing retinitis occurs in 25% of AIDS patients, mainly in late stages, and is rapidly blinding if untreated. Culture of blood, urine, or lungs confirms diagnosis. Rx: intravitreal ganciclovir.
Hard (waxy) exudate (Fig. 314)
Leaking fluid from vessels leaves behind a waxy, yellowish proteinaceous residue. It is seen most often in diabetes, but also in papilledema (Fig. 311) and hypertension.
Drusen (Fig. 315)
This is a hyaline thickening of Bruch’s membrane of the retina (do not confuse with disk drusen). These are round, dull white, bilateral, and uniformly distributed, unlike asymmetric, yellow, irregular, waxy exudates. Drusen may progress to macular degeneration.
Diseases of retinal vessels
Retinal vessel walls are normally transparent. The vessels are visualized because of the blood within them. In arteriosclerosis, as the vessel walls become hyalinized they develop
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Fig. 312 Cotton-wool spots in AIDS.
Fig. 313 White inflammatory cells in Cytomegalovirus retinitis. Courtesy of Joseph Walsh.
Choroid
Sclera
Fig. 316 Retinal cross section.
Fig. 314 Exudate in background diabetic retinopathy.
Fig. 315 Drusen in early macular degeneration due to thickening of Bruch’s membrane and degeneration of overlying retinal pigment epithelium.
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a dull “copper wire” and then a ”silver wire“ reflex, and the relative thickness of artery to vein decreases (Figs 317 and 319).
Hypertensive retinopathy
Scheie classification
IThinning of retinal arterioles relative to veins
Stages I and II are similar to arteriosclerosis of aging
IIObvious arteriolar narrowing with focal areas of attenuation
IIIStage II, plus cotton-wool spots, exudates, and hemorrhages
Stages III and IV are medical emergencies referred to as malignant hypertension. Ninety percent die in
1 year if not treated
IV |
Stage III plus swollen optic disk |
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resembling papilledema |
At their junctions, the arteries and veins share a common sheath. Thickening of the arteriole causes indentation of the venule, referred to as A-V nicking (Fig. 319) inferior to the disk. This can lead to a retinal vein occlusion.
Fig. 317 Engorgement of distal vein with flame hemorrhages due to pressure from thickened arterial wall (A-V nicking). Also, as the wall thickens, the crossing changes from an acute to a right angle.
Fig. 318 Stage III malignant hypertension with cotton-wool spots, flame-shaped hemorrhages, and arteriolar narrowing.
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Fig. 319 Arteriosclerosis with partial vein occlusion demonstrated by engorged vein inferiorly and a secondary flame hemorrhage. “Silver wire” changes are noted at the superior disk margin and irregular narrowing of the artery is noted on the left superior side of the figure.
Retinal vein occlusion
Retinal vein occlusions cause a painless decrease in vision with hemorrhages extending to the peripheral retina. Acutely, there are flame-shaped hemorrhages (Fig. 321) and dot and blot hemorrhages The flame hemorrhages clear in several months. Dot and blot hemorrhages (Fig. 322) may last for years. Cotton-wool spots and a poorly reactive pupil usually indicate an ischemic retina due to a total occlusion. Ischemia is confirmed with fluorescein angiography. The ischemia could stimulate secretion of vascular endothelial growth factor (VEGF) causing new blood vessel growth on the iris. Eventually, tortuous collateral vessels are sometimes seen on the optic disc. If macular edema occurs, it may be treated with localized laser to the retina and/or intravitreal steroid injection.
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Fig. 321 Central retinal vein occlusion |
Fig. 320 Preretinal hemorrhage |
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with superficial flame-shaped |
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between retina and vitreous. |
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hemorrhage following contour of |
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nerve fiber layer. |
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Nerve fiber layer
Sensory retina
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RPE |
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Choroid
Sclera
Fig. 324 Cross section of the retina.
Fig. 322 Deep retinal hemorrhage in partial central retinal vein occlusion.
Fig. 323 Disciform macular degeneration with subretinal hemorrhage (under retinal pigment epithelium) more grayish in appearance.
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Optical coherence tomography (OCT) is a new technology to obtain high-resolution cross-sectional images of the eye. It is analagous to ultrasound except uses light instead of sound. It is especially useful to monitor macular edema (Figs 325 and 326) and macular holes (Figs 353 and 354).
Depths of retinal hemorrhages
(Figs. 320–324)
Preretinal hemorrhages (Fig. 320)
Preretinal hemorrhages occur between the vitreous and retina and may layer out to a boat shape. They are often caused by proliferative diabetic retinopathy with breakthrough into vitreous. Trauma and vitreous detachments are also common causes.
Superficial flame-shaped hemorrhages
(Fig. 321)
These occur in the nerve fiber layer radiating from the optic disk. They occur most commonly in central retinal vein occlusion, papilledema, diabetes, hypertension, and optic neuritis.
Deep retinal hemorrhages (Fig. 322)
Dot and blot hemorrhages occur most often in diabetes, papilledema, and venostasis conditions, such as retinal vein occlusion.
Subretinal hemorrhages (Fig. 323)
In disciform macular degeneration these lie under the retinal pigment epithelium (RPE) and are, therefore, darker red. Retinal vessels overlie subretinal hemorrhages.
Other retinal vessel wall changes
Retinal blood vessels appear white when inflamed. Arteritis occurs in sarcoidosis
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