Our eyes are always unconsciously scanning the environment. It’s called the orienting reflex. The movement stops and the focus intensifies if the stimulus striking the retina signals danger or is a sexual object. Evolution provided us with this survival and reproductive edge. Most other things that are seen are lower priority unless we concentrate on them. Choose wisely! The retina is the sensory layer of the eye, extending from the optic disk to the ora serrata (Figs 458–461), and has the highest cellular metabolic activity in the body. Light stimulates 120 million rods, which are mainly located in the peripheral retina. They are very sensitive to small amounts of light critical for night vision. Five million cones, located primarily in the fovea and macula, are responsible for the acute vision needed to read. Both receptor types transmit the message to the ganglion cell on the retinal surface. The long ganglion cell axons exit the eye in the optic nerve, which synapses in the brain (Fig. 462). Blood is supplied to the inner retina by the central retinal artery (Figs 459 and 507) and the outer retina by the choroidal vessels (Figs 378, 462 and 463). Fig 458 Posterior retinal landmarks. Fig 459 Posterior retina. Fig 460 Cross‐section of peripheral retina. Fig 461 Peripheral retina. The macula is 5 mm in diameter, and its boundaries are defined by the retinal vessels at its margin Fig 459 and cover upper left. In its center is a 1.5‐mm avascular pit called the fovea (Fig. 463), which produces a light reflex. This reflex decreases with age, and its absence in a young individual with a visual disturbance could indicate macular dysfunction (Compare Figs 490 and 490 and 493). When the macula is destroyed, the vision is 20/200 at best. Optical coherent tomography (OCT) is a noninvasive office device (Figs 338, 339, and 463) that reflects light off the macula at a speed of up to 100,000 scans/s. It may be produced in color or black and white. Resolution to as little as 3 μm has allowed the study of tissues to a cellular level. Low reflectivity appears as black, optically empty space and occurs within a normal vitreous and in cystic areas containing serous fluid and edema. High reflectivity appears white, as with solid membranes (Fig. 463), blood drusen, RPE, choroidal nevi, and scars. It is used to discern fluid within the layers of the retina, especially with respect to macular edema (Figs 490, 499, 500 and 563). It is especially helpful in evaluating the vitreoretinal interface; macular holes (Figs ); age‐related macular degeneration (AMD) (Figs 517, 522, 524); and epiretinal membranes (Figs 563 and 572). Optical coherent angiography (OCTA) measures reflections from moving blood and has an advantage over fluorescein angiography because this test is noninvasive and can distinguish capillary structure in the superficial to the deeper retina and choroid (Figs 465, 488B, 505, 506. 507, 508 and 524). Fig 462 Schematic cross‐section of retina. The choroidal blood nourishes the retinal pigment epithelium (RPE) which, in turn, supports the rods and cones. The inner nuclear layer horizontally interconnects the input. Fig 463 OCT of normal macula with central foveal pit. Note choroidal‐scleral junction (19). The choroidal vessels (16, 17, 18) nourish the retinal pigment epithelium (15) which, in turn, metabolically support the overlying rods and cones that make up the outer nuclear layer. The inner nuclear layer (7) contain the cell bodies that create horizontal synapses interconnecting the stimuli from the rod and cone receptors. The ganglion cells (5) and their axons (4) then exit the eye forming the optic nerve. Source: Courtesy of Carl Zeiss, Meditec, Inc. Fig 464 OCT ‐ Plaquenil toxicity causing disruption of outer retina including the rod and cone receptors (compare with normal OCT Fig. 463). Source: Courtesy of Zeiss Meditec, Inc. The fundus refers to the inner part of the eye. It is evaluated with an ophthalmoscope. Eye doctors usually dilate the pupils for this exam. Tropicamide (0.5–1%) (Table 15, p. 147), which relaxes the pupillary sphincter, is preferred because of its quick action (5–10 minutes) and strong effect. Phenylephrine (2.5–10%), which stimulates the dilator muscle, has a weaker effect and takes longer to act (30 minutes). An advantage of phenylephrine is that it does not cause the patient’s sight to blur as much and would not be as problematic for them when driving home. Both drugs are often used together when peripheral retinal disease is suspected. Fig 465 Normal color OCTA of perifoveal retina. Superficial retinal vessels are orange, deep retinal plexus vessels are green. Source: Courtesy of Carl Zeiss, Meditec, Inc. The macula is examined last to minimize miosis and discomfort. A direct ophthalmoscope (Fig. 466) allows for monocular visualization of the posterior half of the fundus, where most retinal pathology is located. Use a negative lens (red) for myopic eyes and a positive lens (black) for hyperopic eyes. Get as close to the eye as possible and minimize movement by resting the hand that is holding the ophthalmoscope on the patient’s cheek, while your other hand lifts the patient’s upper lid. A binocular indirect ophthalmoscope (Fig. 467) consists of a light source worn over the head and a hand‐held lens, which allows the retina to be seen in three dimensions, albeit upside down. Retinal holes and detachments at the ora serrata can be viewed by indenting the sclera with a small thimble worn on the index finger (Fig. 461). Fig 466 Direct ophthalmoscope. Fig 467 Indirect ophthalmoscope. A three‐mirror contact lens (Figs 468 and 469), used with a slit lamp, gives a detailed stereoscopic 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 gelatinous solution on the eye. Fig 468 Three‐mirror contact lens. Fluorescein dye is injected intravenously. As it passes through the retinal circulation, fundus photographs are made in a rapid sequence. The dye first appears in arteries in 13 seconds and the veins in 19 seconds. Later images may show leakage and staining of tissues (Figs 477A, 481, 484, 499, and 502). The blood‐retinal barrier normally prevents leakage from vessels (Fig. 470). This test is useful for evaluating retinal circulation. It demonstrates rate of flow, leakage from capillaries, staining of tissues, areas of nonperfusion, and neovascularization (Figs 483, 484, 499, 502, and 530). Indications for this invasive test may decrease as improvements continually occur in noninvasive optical coherence angiography. Fig 469 Three mirror contact lens allows detailed three‐dimensional visualization of the retina and the angle between the iris and cornea. Note: Image showing use of lens at slit lamp. Fig 470 Normal fluorescein angiogram. Retinal vessels terminate at the perifoveal area of the macula. Foveal blood supply comes from underlying choroidal capillaries. The blood‐retinal barrier normally prevents leakage from capillaries (see Fig. 502). Fig 471 Normal tigroid (tessellated) fundus with pigment around disk and deeply pigmented choroid. The optic disk is normally orange–red with a yellow cup at its center. The retinal artery and vein pass through the optic cup and bifurcate on the surface of the disk. Proliferation of the retinal pigment epithelium (RPE) at the disk margin is a normal finding (Fig. 471). In axial myopia, the eye is increased in length and the retina may be dragged away from the optic disk margin, exposing the sclera. This is called a myopic conus or crescent (Fig. 472A). In extremely myopic eyes, often greater than 10 D—referred to as pathologic myopia—the retina is stretched so thin that it is totally absent in some areas (Fig. 472B). Fig 472A Normal myopic conus (crescent) at disk margin. 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. 474). The disk margin may also be obscured by drusen (Fig. 473), which are small, round, translucent bodies made up of hyaline deposits that are often calcified. They occur in 0.3–3.7% of eyes. When superficial, they are easy to identify; but when buried, B‐scan ultrasound and CT scanning are needed to reveal calcification (see Figs 479 and 480). Drusen may damage nerve fibers and cause an enlarged blind spot. Fig 472B Pathologic myopic happens most often in eyes with more than 10 D of refractive error (Fig. 22). The globe is elongated causing the retina and choroid to be stretched so thin that it causes patchy areas of atrophy exposing the underlying white sclera. Source: Courtesy of University of Iowa. Fig 473 Disk drusen are not related to retinal drusen that occurs in macular degeneration (Figs 516 and 537). Fig 474 Myelination of the optic nerve. The white myelin sheath covering the optic nerve occasionally extends to the interior of the eye. Papilledema is swelling of the optic nerve specifically due to elevated intracranial pressure that causes a reduction in the ability of fluid to exit the eye. It is usually bilateral and always serious. The intraocular congestion results in a swollen, elevated optic disk with blurred margins (Figs 475–478). As it progresses, veins become engorged and flame‐shaped hemorrhages and cotton‐wool spots develop in the peripapillary area (Figs 476, 478). Fig 475 OCT image of papilledema showing elevated disk margin and hyporeflective (black) areas corresponding to edematous fluid in and around the optic disk. Note normal foveal pit temporal to disk. Source: Courtesy of Elizabeth Affel, Wills Eye Hospital. In 80% of normal eyes, ophthalmoscopic examination reveals subtle pulsations of the retina 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 pulsations. Edema of the optic disk may extend to the surrounding retina causing enlargement of the blind spot (Figs 132,134, and 477B). If the fluid extends to the macula, it may reduce central vision (Fig. 478). The central and peripheral vision with the OCT are the safest noninvasive tests to monitor progression or resolution papilledema, since serial spinal taps and fluorescein angiography are more dangerous. Papilledema due to elevated intracranial pressure often causes headache, confusion, nausea, and visual obscurations. Diplopia occurs if the pressure compromises the sixth cranial nerve. Prolonged increased pressure can permanently damage the brain and optic nerve. Common causes are side effects of drugs, such as tetracycline, excessive vitamin A, and retinoids used to treat severe acne and psoriasis. Intracranial brain tumors, hemorrhages, and infections could also elevate intracranial pressure. Fig 476 Papilledema with elevated disk, engorged veins, and flame‐shaped hemorrhages. Fig 477A Fluorescein angiogram of papilledema reveals leakage in and around the optic disk. Fig 477B An enlarged blind spot can be plotted most accurately on a tangent screen. Visual field testing of the size of the blind spot and contraction of the peripheral field and OCTs must be monitored closely since this is often the only way to know how the papilledema is being controlled, since serial spinal taps and fluorescein angiograms have more risk. Idiopathic intracranial hypertension (pseudotumor cerebri) is a common cause of papilledema. It occurs most often in young overweight women and may be first discovered by noting papilledema during a routine eye exam. Chronic, unrelenting headaches in all patients, but especially these obese women, should remind us to rule out papilledema. Fig 478 Papilledema with macular star (↑) due to extension of disk edema. There are many conditions that can mimic the optic disk changes of papilledema and every clue must be considered. A swollen disk caused by optic neuritis (Fig. 118) is associated with a Marcus Gunn pupil (Fig. 119) and loss of central vision; whereas in early papilledema, the pupil is normal and there is usually no loss of visual acuity unless the disc edema extends to the macula (Fig. 478) or if optic atrophy has already occurred (Fig. 116). Early papilledema may also be difficult to be distinguished from drusen of the disk (Fig. 473) and myelinated nerve fibers (Fig. 474). Both blur the disk margin and cause an enlarged blind spot (Fig. 477B). On fluorescein angiography, however, only papilledema has leakage of dye (Fig. 477A). Like papilledema, central retinal vein occlusion (Fig. 510) may have venous engorgement, flame hemorrhages, a blurred disk margin, and cotton‐wool spots. Unlike papilledema in central retinal vein occlusion (Fig. 510), the flame hemorrhages extend out to the peripheral retina and there is more loss of vision. Malignant systemic hypertension (blood pressure 220/120 mmHg) (Table 17, p. 179) also causes a papilledema‐like retinal appearance, which is distinguished by measuring blood pressure on all patients with blurry disk margins (Figs 486 and 488A). Orbital diseases decreasing venous outflow from the eye can cause swelling of the disk (Fig. 124). Causes include orbital tumors and infections; idiopathic inflammation of the orbit, also called orbital pseudotumor (Figs 226–229B), must be considered. Do not confuse orbital pseudotumor with pseudotumor cerebri (p. 175). In orbital diseases, one looks for localizing signs, such as proptosis. Cavernous sinus disease can also obstruct venous drainage from the orbit (Figs 144–146). Fig 479 B‐Scan ultrasound showing hyperreflective calcification from buried optic disk drusen, which could blur disk margins, confusing it with papilledema. Courtesy of Jonathon Prenner, MD, UMDNJ. Fig 480 CT scan performed during workup of what was thought to be papilledema instead revealed calcified optic disk drusen. Source: Courtesy of Elliot Davidoff, MD, Ohio State Medical School. The retina, brain, and kidney share similar vascular anatomic features and physiologic properties. The retina affords a window into microvascular diseases in these organs. In Alzeimer’s disease there may be a loss of retinal blood vessels especially in the perifoveal area. The diagnosis and progression of diabetic kidney disease can be assessed by following the severity of diabetic retinopathy ‐ see cover. Retinal vessel walls are normally transparent. They can be visualized because of the blood they contain. In arteriosclerosis, as the vessel walls become thickened they may develop a silver wire appearance (see cover). Fig 481 Fluorescein angiogram of vasculitis causing loss of the blood‐retina barrier. Source: Courtesy of Optos Instruments. The vessel walls may also whiten when inflamed (Figs 407 and 481) in conditions such as systemic lupus erythematosus, sarcoidosis (Fig. 407), cytomegalovirus infection (Figs 419 and 534), sickle cell disease (Figs 482–484), giant cell arteritis (Fig. 122), toxoplasmosis (Fig. 408), and syphilis. Damaged vessel walls may eventually develop a permanent white sheath and a threadlike lumen (Fig. 496). Loss of blood flow, as occurs in a retinal artery occlusion, diabetes, hypertension, sickle cell disease, and choroiditis may also cause these changes. The resulting ischemia to the ganglion cells may cause cotton‐wool spots (cover and Fig. 533). Fig 482 Sickle cell retinopathy with vascular inflammation (↑), pale areas of ischemic retina salmon‐patch intraretinal hemorrhages (↑↑), and pre‐retinal hemorrhages (↑↑↑). This occurred in a 26‐year‐old black male presenting to the emergency department with an acute myocardial infarction, renal failure, and cholecystitis. Abnormal capillaries may grow inside the eye in a misguided response to ischemia most commonly due to diabetic retinopathy. They are due to liberation of vascular endothelial growth factor (VEGF) in response to retinal ischemia. Panretinal photocoagulation (PRP) may be used to destroy large areas of hypoxic retina, thus decreasing the oxygen demand and the secretion of vascular endothelial growth factor (VEGF). A total of 1500 laser burns are usually administered to each eye in two sessions (back cover). In compliant patients—able to return for multiple visits—anti‐VEGF injections are an alternative to laser PRP for proliferative retinopathy, since the latter significantly reduces peripheral vision. Fig 483 Sickle cell retinopathy with compensatory neovascularization at edge of infarcted retina with the appearance of a sea fan. Source: S. Cohen, et al., Diagnosis and Management of Ocular Complications of Sickle Hemoglobinopathies: Part II. Ophthalmic Surg Lasers Imaging Retina., 1986, Vol. 17, No. 2, pp. 110–116. doi:10.3928/1542‐8877‐19860201‐12. Reprinted with permission from SLACK Incorporated. Fig 484 Fluorescein angiogram showing leakage from abnormal new vessels. Source: S.B. Cohen et al., Ophthal. Surg., 1986, Vol. 17, No. 2, pp. 110–116. Reprinted with permission from SLACK, Inc. Introduced in 2006, there currently are four anti‐VEGF drugs—ranibizumab (Lucentis), bevacizumab (Avastin), brolucizumab (Beovu), and afibercept (Eylea)—which, when injected into the vitreous, (Figs 526 and 527) cause regression of the abnormal vessels. In 2020, Beavu was reported to cause retinal vasculitis. They are now being used as a first‐line treatment of wet macular degeneration and for macular edema due to retinal vein occlusions and diabetic retinopathy. In the USA, 6 million injections were given in 2016, and the indications continue to grow. It is the most common intraocular procedure, even doubling the number of cataract extractions. Sickle cell hemoglobinopathy leads to red cells taking on a sickle shape in deoxygenated blood (Figs 482–484). Sickle cell trait (HbAS) affects 8% of African Americans, with 0.4% having sickle cell disease (HbSS) and 0.2% having HbSC disease. Retinal neovascularization resembling “sea fans” occur at the edge of infarcted (pale) areas. Confirm with a sickle cell preparation where a deoxygenating agent is added to the patient’s blood. It is positive if red blood cells assume a crescent (sickle shape). Treatment with laser or intravitreous anti‐VEGF is aimed at eliminating these abnormal vessels, which could bleed into vitreous causing fibrotic membranes that could contract and cause retinal detachment (RD) (Figs 485, 504, 562, and 579). Normal blood pressure (BP) is now considered to be 120/70 or less. Any BP above that is associated with a progressive increase in the risk of heart attack and stroke. The cost, stigma of having a disease, and the side effects of medical treatment usually cause physicians to postpone medicating until BP reaches 140/80 or more. Criteria for treatment varies, but a general rule is to wait for 150/90 in people over age 60 to prevent falls resulting from decreased blood flow to the brain. In diabetics, treatment may be started at levels 10 mm/Hg less than would otherwise be indicated, since both conditions adversely affect the vessels. Fig 485 Retinal detachment. Source: Alila Medical Media/Shutterstock.com. Table 17 Scheie classification of hypertensive retinopathy (see Fig. 486). At their junctions, the arteries and veins share a common sheath. As the arteriole wall thickens (arteriosclerosis), it takes on a silvery appearance and causes indentation of the venule, referred to as A–V nicking (Fig. 487). This can lead to a retinal vein occlusion. Retinal vein occlusions occur in 0.5% of people. The most common cause is aging followed by hypertension. Patients usually present with a sudden, persistent, painless decrease in vision. Retinal flame‐shaped and dot‐and‐blot hemorrhages (Figs 487–489, 510 and 512) extend into the periphery and may last for years. Cotton‐wool spots and a poorly reactive pupil usually indicate an ischemic retina, which are very ominous. Ischemia is confirmed with fluorescein angiography or OCT angiography (OCTA; Figs 490 and 491). Ischemic cases stimulate secretion of the vascular endothelial growth factor (VEGF) causing new blood vessel growth on the iris, which can bleed and lead to glaucoma (Figs 388 and 389). Not all new vessels are bad. Late‐onset, tortuous, retino‐choroidal, collateral vessels could develop on the optic disk, and elsewhere in the retina, and are beneficial in helping the obstructed venous blood to exit the eye via the choroidal route (Fig. 489). If macular edema occurs, it is usually treated with intravitreal injections of anti‐VEGF or steroid (Figs 526 and 527). Time between injections may vary with responses and is referred to as treat and extend. There are corticosteroid intravitreal implants that provide a prolonged slow release (Fig. 492 and Table 13, p.144). Therapy continues until resolution of edema occurs as determined by retinal thickness on OCT (Figs 490 and Figs 490 and 493) and return of visual acuity. Treatment should also address the frequently associated risk factors such as hypertension, dyslipidemia, diabetes, and hypercoagulability of the blood. Fig 486 Stage III hypertensive retinopathy with cotton‐wool spots, flame‐shaped hemorrhages, and arteriolar narrowing (see Table 17, p. 179). Fig 487 Drawing of branch retinal vein occlusion with flame hemorrhage and a A–V nicking. As the arteriole wall thickens, the A–V crossings change from an acute to a right angle. Fig 488A Arteriosclerosis with partial vein occlusion causing an engorged vein inferiorly and a secondary flame hemorrhage. “Silver wire” changes are noted at the superior disk margin. Fig 488B OCT‐A of partial vein occlusion with dilated tortuous veins and capillaries. Source: Courtesy of Carl Zeiss Meditec, Inc.
Chapter 10
The retina and vitreous
Retinal anatomy
The macula
Fundus examination
Fluorescein angiography
The optic disk (papilla)
Papilledema (choked disk)
Pseudopapilledema
Retinal blood vessels
I
Thinning of retinal arterioles relative to veins
Stages I and II are similar to arteriosclerosis of aging.
II
Obvious arteriolar narrowing with focal areas of attenuation
III
Stage II, plus cotton‐wool spots, exudates, and hemorrhages (Fig. 486)
Stages III and IV are medical emergencies and have strong association with death.
IV
Malignant hypertension, blood pressure 220/120 mmHg
Stage III plus swollen optic disk resembling papilledema
Retinal vein occlusion (RVO)
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