SYSTEMIC AND VASCULAR DISEASE

Congenital ON pit: usually inferotemporal disk; may use laser to demarcate between fovea and ON.

Choroidal tumors: such as hemangioma, metastatic cancer, leukemia, melanoma, and osteoma

Retinal hole in high myopes: macular holes usually just have a cuff of SRF, but in high myopes, fluid does not resolve and may need vitrectomy with gas placement.

Vasculopathy: malignant hypertension (often with bilateral ON swelling), toxemia of pregnancy, collagen vascular disease, disseminated intravascular coagulation (DIC), etc.

Choroidal inflammatory disease: Harada’s disease (often have pinpoint hyperfluorescent spots that leak), sympathetic ophthalmia, and other posterior uveidites

Others: idiopathic uveal effusion, ocular contusion, AMD, chronic steroid use (thick and cloudy SRF, with many RPE defects), and syndrome of RRD, choroidal effusions, hypotony, and panuveitis (treat with steroids first, then fix RD).

TRACTIONAL RETINAL DETACHMENT (TRD) Second most common type of RD; from vitreoretinal fibroproliferative membranes that mechanically pull the retina away from the RPE. Typically presents with a smooth retina that is concave toward the anterior segment; usually confined, and rarely extends to the ora serrata. Retinal tears may result in combined TRD and RRD.

VITAMIN A DEFICIENCY Results in night blindness; patients are prone to measles and smallpox, which may lead to severe corneal scarring.

Systemic and Vascular Disease

ACQUIRED PARAFOVEAL OR IDIOPATHIC JUXTAFOVEAL TELANGIECTASIAS Mild vasculopathy with retinal thickening usually temporal to the macula, characterized by right-angle venules (horizontal vessels that dive deep into the retina). Patients typically are age 40 to 65, F > M, and have mildly decreased VA from CME or rarely from CNVM. Types Ia, Ib, II (most common). May be thought of as ‘‘localized Coats’ disease’’; FA shows dilated capillaries with late leakage. Disease is slowly progressive and associated with diabetes. Does not respond well to treatment, but may try focal or grid laser.

ARTERIOSCLEROSIS Begins as arteriolar-venous nicking that becomes more marked, then ‘‘copper wiring’’ (hypercellularity), and finally ‘‘silver wiring’’ (collagen deposition).

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272 RETINA AND VITREOUS

BRANCH RETINAL ARTERY OCCLUSION (BRAO) Superficial retinal whitening along a blocked arteriole; 90% occur in the temporal arcades. Good prognosis; 80% improve to 20/40 VA or better. May occur from thrombosis or emboli. Emboli may be Hollenhorst plaques, yellow cholesterol emboli from the carotid (check carotid duplex) or less commonly calcific plaques from a cardiac valve (check echocardiogram).

Susac syndrome: multiple recurrent BRAOs from microangiopathy of unknown etiology affecting brain, retina (usually bilateral), and cochlea. Onset usually at age 30; self-limited disease over 4 years. May treat with steroids, antiplatelets, and calcium channel blockers.

BRANCH RETINAL VEIN OCCLUSION (BRVO) Blocked retinal vein (usually temporal arcades) most commonly from compression at an arteriovenous crossing (because they share a common adventitial sheath). Typically presents with painless decreased VA in 75% (40% are better than 20/50, 66% better than 20/200) or VF loss with pie-shaped distribution of retinal hemorrhages (usually flame), microaneurysms, CWS, edema, distended and tortuous veins, and slightly decreased IOP. Occurs in M ¼ F, average age 65; from hypertension (70%), arteriosclerosis, and POAG (12%). May be ischemic (>50%).

Fifteen to 20% have occlusion in the fellow eye within 5 years. Usual course is gradual resorption of the hemorrhage and edema over months; however, may have occlusion of macular capillaries with chronic CME, retinal NV in 20%, NVD 10% (only 1% have NVI), or RD. If >4 DD of nonperfusion, then 62% have NV. Overall, 1% of nonischemic versus 54% of ischemic BRVOs have retinal NV, usually within 2 years.

Macular branch retinal vein occlusion: superior vein in 85%; CME treatment with laser.

Treat underlying conditions. Photocoagulation for CME or NV. Complications may include a rapid progression to ‘‘90-day glaucoma’’ (retinal ischemia, leading to NV, then NVI and glaucoma).

BVO Study (multicenter, randomized controlled trial, 1977–1985): use grid laser after 4 months for CME if VA is 20/40 or less and there is good macular perfusion. Sixty-three percent of treated versus 36% of untreated eyes gained two or more lines of VA; follow-up at 3 years showed average VA 20/40 for treated versus 20/70 for untreated eyes (neither group returned to 20/20). Segmental PRP is recommended only for NV (only 12% of ischemic BRVO developed significant VH).

CANCER-ASSOCIATED RETINOPATHY (CAR) Paraneoplastic process of decreased retinal function that may have normal-appearing fundus, associated with systemic cancer. Typically presents with scintillations, acquired nyctalopia, or decreased vision or visual field.

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Bone marrow transplant (BMT) retinopathy: combination of radiation and chemotherapy toxicity.

CENTRAL RETINAL ARTERY OCCLUSION (CRAO) Painless, profound vision loss over seconds (may have history of amaurosis fugax or transient visual obscuration) with immediate APD, macular cherry red spot, and opaque inner retina; may have thinned arteries or ‘‘box carring.’’ Emboli in arterial system seen in 20% of cases (poor prognostic sign; 59% mortality within 9 years); 25% have sparing of cilioretinal artery with preserved VA. Irreversible damage occurs within 90 minutes. FA shows delayed arterial filling, delayed AV transit time, normal choroidal pattern (unless there is an ophthalmic artery occlusion), and late disk staining. Loss of inner retina is noted by a decreased ERG B wave. VF may show a remaining temporal island. Rubeosis occurs in 15% of cases, NVG in 11%.

Etiology: atherosclerosis (leading cause in older patients), often accompanied by hypertension (67%), carotid atherosclerosis (45%), and diabetes (25%). Cardiac valvular disease causes 25% of cases; rule out GCA. Mean survival status post-CRAO is 5.5 years, compared with 15.4 years for age-matched controls. In younger patients, migraine causes one third of CRAO. Other causes include trauma (especially male patients), hypercoagulable state (oral contraceptives, pregnancy, etc.), embolic source (carotid, cardiac, intravenous drug abuse), cocaine use, collagen vascular disease, hyperhomocystinemia, and sickle cell disease.

Treatment: no proven best therapy, but emergently may try to decrease IOP (ocular massage, AC paracentesis, beta-blockers, Diamox, mannitol), increase retinal oxygenation (carbogen, hyperbaric chamber), or improve vascular flow with fibrinolytic agents (intra-arterial tissue plasminogen activator).

CENTRAL RETINAL VEIN OCCLUSION (CRVO) Second most common retinal vascular disorder after diabetes. Retinal hemorrhage is seen in all four quadrants from venous thrombosis at the cribriform plate. May also have hemicentral or hemispheric retinal vein occlusion if the superior or inferior retinal vein is occluded.

Signs and symptoms: decreased VA (usually from CME) or loss of VF with CWS, NFL hemorrhages, and dilated and tortuous vessels, often described as ‘‘blood and thunder’’; may have slightly lower IOP in affected eye and delayed venous filling on FA.

Signs of prior CRVO (once resolved, fundus may look nearly normal): collateral vessels on the disk (not NV vessels that leak) and vessels that cross the midline raphae.

If the thrombosis is behind the cribriform plate, patients usually have more disk swelling but less retinal ischemia as they develop more collateral vessels and have a better visual prognosis. If

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274 RETINA AND VITREOUS

thrombosis is anterior to the cribriform plate, there is less disc swelling, but more retinal hemorrhage and ischemia and more decreased VA.

Etiology: hypertension (60%), atherosclerosis (25–50%), diabetes (15– 30%), POAG (6–20%), hyperopia, tight cup, and hypercoagulable state; rule out GCA. Most patients are usually >50 years old (if age <50, most are a result of head trauma or hypercoagulable state from estrogen).

Order work-up if etiology is not obvious, especially in young patients: RPR/MHA-TP, CBC, electrolytes, lipids, ESR, coagulation panel, protein S and C deficiency, ANA, glycohemoglobin, antithrombin III factor, factor V Leiden, anti-phospholipid antibody; rule out hyperhomocystinemia.

Nonischemic: accounts for up to 66% of CRVO. Seen in younger patients; characterized by milder signs with venous tortuosity, mainly affecting the posterior pole with retinal hemorrhages, rare CWS, and mild CME, and only 10 to 20% progress to ischemic. ERG B:A >1.0 (normal). Follow every 2 months for 1 year; majority of patients are 20/50 or better. No treatment is usually indicated.

Papillophlebitis is type of CRVO from inflammatory venous vasculitis with nonischemic occlusion and residual vessel sheathing and optociliary shunt vessels.

Ischemic: accounts for up to 33% of CRVO. Seen in older patients; characterized by severe loss of VA and VF, with confluent intraretinal hemorrhages in the posterior pole (flame hemorrhages predominant), engorged venous tree, and numerous CWSs (a marker for ischemia; if >10, then 75% develop NVG). Severe capillary dropout is seen on FA; ERG B:A <1.0.

Outcome: hemorrhage, CWS, and venous tortuosity gradually resolve; may have residual optociliary shunt vessels, arteriolar narrowing, optic atrophy, or APD. Twenty-five percent of patients will have a contralateral occlusion within 5 years. Retinal NV is rare, but NVI is more common, and 50% develop NVI,

NVA, then NVG (especially if >50% capillary nonperfusion), which may occur as early as 2 weeks, but 92% occur within 6 months (thus, follow patients closely early).

Treat underlying systemic conditions (does not affect CRVO outcome except possibly hyperviscosity etiology). Not beneficial: anticoagulants, fibrinolytics, carbogen, steroids, hyperosmotics, vitamins, and prostacyclin. May consider ON sheathotomy.

Scatter photocoagulation should be offered if >50% nonperfusion on FA with 1000 to 1200 spots; prevents and regresses NV, but no effect on final visual outcome (unlike BRVO).

Central Vein Occlusion Study (CVOS) (multicenter, randomized controlled trial, 1988–1994): do not offer prophylatic PRP; wait

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until NVI or NVA develops. Risk factors to develop 2 o’clock hours of NVI or NVA: 36% if 30 to 74 nonperfused disk areas on FA, 52% if >75 disk areas, retinal hemorrhage >standard photo 2a, <1 month duration, and female gender. FMG not recommended for CME.

Complications: acute angle-closure glaucoma from increased posterior pressure and ‘‘90 day glaucoma’’; neovascular glaucoma can occur as late as 24 months.

CILIORETINAL ARTERY OCCLUSION Artery is present in 32% of normals and fills in the choroidal phase of the FA, as it is a branch of the posterior ciliary artery. Blockage causes decreased VA from macular ischemia and possible CME. Forty percent are isolated cases; do work-up like CRAO, and rule out GCA. Ninety percent improve to 20/40 or better. Forty percent are combined with CRVO probably from ON edema compressing the cilioretinal artery, and 70% return to 20/40 or better. Fifty percent are associated with ischemic optic neuropathy with poor vision (20/400 to NLP), as both are from posterior ciliary artery insufficiency.

DIABETIC RETINOPATHY (DR) Diabetes causes a diffuse vasculopathy and is the leading cause of preventable blindness in the United States. Vasculopathy is symmetric (only 5% of PDR have high-risk characteristics in one eye and less than moderate NPDR in the fellow eye) and classified as nonproliferative or proliferative. Nonproliferative disease is characterized by dot-blot hemorrhages (deep retina), microaneurysms, hard exudates (distinct yellowish lipoprotein deposits deep in retina), NFL infarcts (called CWSs, but they are not soft exudates), intraretinal microvascular abnormality (IRMA; localized NV confined to the retina that does not leak on FA). Proliferative DR adds the characteristic of retinal NV and fibrous glial proliferation with possible tractional RD. Vision loss may be due to retinal hemorrhages, macular ischemia, diabetic macular edema, tractional RD, or lens edema with myopic shift (lenticular retention of sorbitol from elevated blood sugar). Vascular endothelial cell growth factor (VEGF) injected into mice causes NV. PRP destroys tissue to decrease VEGF.

Pathology: loss of pericytes (supporting cells for capillary endothelial cells), leading to capillary leakage and dropout, and basement membrane thickening. A classic ophthalmic finding is lacey vacuolization of the iris pigment epithelium.

Two types of diabetes:

Insulin-dependent diabetes, type 1, adolescent-onset: typically from premature failure of pancreatic islet cells to produce insulin. Twenty-five percent of patients have DR after 5 years with the disease, 60% at 10 years, and 80% at 15 years, and 25%

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276 RETINA AND VITREOUS

of these have proliferative diabetic retinopathy (PDR). Examine these patients within 5 years of diagnosis. Growth hormone released during adolescence may be associated with progression of retinopathy.

Non–insulin-dependent diabetes, type II, adult-onset: usually from acquired insulin resistance. Initial ophthalmic exam should follow the diagnosis.

Risk factors for DR progression: elevated serum glucose or glycosylated hemoglobin, hypertension, years with disease, nephropathy, and hyperlipidemia. Factors that retard DR progression: ipsilateral glaucoma, ipsilateral chorioretinal scarring, but not ipsilateral carotid stenosis.

Diabetes Control and Complication Trial (DCCT): showed delayed onset of DR, nephropathy, and neuropathy in type 1 diabetic patients with tight glucose control.

Wisconsin Epidemiological Studies of DR (WESDR): showed

that patients with intensive glucose control (glucose <180), as well as hypertension and hyperlipidemia control, had 80% less progression of DR in patients with no retinopathy, 65% less progression in patients with mild to moderate DR; patients with more severe DR had the same risk reduction as patients with milder DR but showed a temporary ‘‘early worsening’’ effect.

Sorbinil Retinopathy Trial (SRT): showed that aldose reductase was not effective.

Early Treatment of Diabetic Retinopathy Study (ETDRS): looked at aspirin use and VH risk, and defined treatment parameters for clinically significant macular edema (CSME) and PRP for NPDR.

DIABETIC RETINOPATHY: CLINICALLY SIGNIFICANT MACULAR EDEMA (CSME) Diabetic macular edema (DME) may be focal, diffuse, or cystoid (outer plexiform or inner nuclear layers) and is the most common cause of diabetic vision loss.

CSME is a clinical criterion that the ETDRS showed benefited from focal laser, with a 50% decreased moderate vision loss (doubling of visual angle). CSME diagnosis requires one of the following:

Elevated or thickened retina within 500 mm of the FAZ

HE within 500 mm of the FAZ associated with thickening

Thickened retina >1 DD and within 1 DD of the FAZ

Although CSME is a clinical diagnosis, obtain FA to further define the leakage prior to laser treatment and to rule out macular ischemia. Poor visual prognosis includes central capillary occlusion, HE in the fovea, VA <20/200, and fixed chronic cysts; if excessive exudate, is present, rule out hyperlipidemia.

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DIABETIC RETINOPATHY: NONPROLIFERATIVE (NPDR) Diabetic vasculopathy that is usually confined to the posterior pole and has not progressed to neovascularization. Usually asymptomatic or has vision loss from CSME or macular ischemia.

Minimal: 1 microaneurysm (Ma)

Mild: 1 Ma plus a retinal hemorrhage, CWS, or HE

Moderate: HE or Ma that is >ETDRS standard photo 2a in one quadrant and IRMA or CWS or venous beading

Severe NPDR: any one of the following ‘‘4-2-1 rule’’ (very severe NPDR is two of these):

Four quadrants of Ma or HE > photo 2a

Two quadrants of venous beading > standard photo 8b

One quadrant of IRMA > standard photo 8a

ETDRS showed that PRP is effective for severe and very severe NPDR, as 15% of severe and 45% of very severe NPDR cases progress to PDR each year. Severe and very severe NPDR and early PDR cases have a 2 to 7% risk of severe vision loss within 2 years and thus warrant at least partial PRP.

DIABETIC RETINOPATHY: PROLIFERATIVE (PDR) Progression of vasculopathy from NPDR to neovascularization. The Diabetic Retinopathy Study (DRS) showed benefit of PRP for PDR.

Early: any NV not meeting criteria for high risk

High risk: 25 to 40% risk of severe vision loss (VA <5/200 on two exams 4 months apart) within 2 years usually from VH. PRP decreases the 5-year loss of vision risk by 50%. High-risk PDR has at least three of these criteria:

Any NV

NV on or within 1 DD of the disk

Moderate or severe NV (either of the following findings):

Neovascularization of the disk (NVD) >1/3 DD, as in photo 10a

Neovascularization elsewhere (NVE) >1/2 DD

Preretinal hemorrhage or VH

Advanced: tractional RD involving the fovea or VH obscuring ability to grade NV

Vitreous hemorrhage: Diabetic Retinopathy Vitrectomy Study (DRVS) showed that early vitrectomy is beneficial for insulin-dependent diabetic patients with VH; 25% regain 20/40 VA or better. ETDRS showed that oral aspirin use does not increase a patient’s VH risk.

DISSEMINATED INTRAVASCULAR COAGULATION (DIC) Systemic platelet and fibrin thrombi in small vessels, causing choriocapillaris occlusions and serous RD, with late multiple RPE changes. Over 100 different causes reported (septicemia, amniotic fluid embolism, snake bite, etc.).

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278 RETINA AND VITREOUS

EMBOLIC VASCULOPATHY Temporary blockage of artery may cause amaurosis fugax, typically from cholesterol embolus (Hollenhorst plaque) that lodges at an arteriole bifurcation.

GIANT CELL ARTERITIS (GCA), TEMPORAL ARTERITIS May cause choroidal nonperfusion via short posterior ciliary arteries with nasal or temporal choroidal ischemia, in addition to temporal arteritis, CRAO, AION, or posterior ischemic optic neuropathy (PION). Treat with IV steroids, then temporal artery biopsy. See Chapter 8.

HYPERLIPIDEMIA A risk factor for atherosclerosis and vascular occlusions; if severe, may cause intraretinal lipid exudation. Lipoproteins have a lipid core surrounded by a plasma membrane containing cholesterol and apolipoproteins (high-density lipoprotein, beta-low-density lipoprotein). Secondary lipoproteinemia is more common than primary and is less severe; usually seen with diabetes, hypothyroidism, nephrotic or hepatic dysfunction, or pancreatitis. Five types of primary hyperlipidemias:

Type 1: increased cholymicrons with very elevated triglycerides; higher incidence of lipemia retinalis.

Type 2: increased cholesterol, beta-lipoprotein; higher incidence of coronary artery disease and arcus senilis but no lipemia

Type 3: increased cholesterol, increased triglycerides

Type 4: increased triglycerides, increased pre-beta-lipoprotein

Type 5: very elevated triglycerides, increased cholymicrons and pre- beta-lipoprotein

HYPERTENSIVE RETINOPATHY Elevated blood pressure may cause acute or chronic retinopathy or choroidopathy.

Acute, acclerated, or malignant hypertension: retinopathy is not as prominent as choroidopathy because of protective retinal vasoconstriction. Mostly see choroidopathy, as the choroid cannot autoregulate; thus, expect infarction of choroidal lobule and overlying RPE changes (Elschnig’s spots), serous RD, and hyperplastic RPE over sclerotic choroidal vessel (Siegrist’s streaks). May have fibrinoid necrosis of the choriocapillaris endothelium with hemorrhage, edema, and exudates. May have optic neuropathy and disk swelling from ischemic axonal swelling.

Four stages of hypertensive retinopathy:

Narrowing of arteries

Focal arteriolar constriction

Hemorrhage and exudates

Papilledema

Chronic hypertensive retinopathy: hyalinization of vessel media with arteriolar narrowing, increased light reflection seen as ‘‘silver wiring’’ (sclerotic phase from collagen deposition), and arteriovenous

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compression or ‘‘nicking’’ (Gunn’s sign), as the arteriole and venule share a common adventitia. Increased incidence of BRVO, BRAO, CRVO, and macroaneurysm.

IDIOPATHIC POLYPOIDAL CHOROIDAL VASCULOPATHY (IPCV) Usually seen in African-American female patients with CNVM from choroidal vascular anomaly; often found peripapillary, and may see the abnormal vessels better with ICG angiography.

MACROANEURYSMS Acquired arteriolar dilatations in the posterior pole within first three orders of retinal bifurcations, most commonly superotemporal. Usually seen in elderly female patients with hypertension and atherosclerosis. Linear breaks in the vessel wall may lead to hemorrhage at any retinal level, especially subhyaloid ‘‘boat-shaped’’ hemorrhages; may also have CME, exudate, or vitreous hemorrhage if a subhyaloid hemorrhage ruptures.

Group I hemorrhagic form (vs. exudative group II) tends to be larger and occur closer to the disk. FA shows a ‘‘light bulb’’ appearance that fills completely in the arterial phase with progressive late leakage.

Usually resolves spontaneously. If macular exudation is present, may photocoagulate directly over the lesion with low energy, long duration, large spot laser. Krypton yellow is probably best, as the laser energy is absorbed by RBCs, but laser may cause hemorrhage, BRAO, ERM, or macular hypoperfusion.

OCULAR ISCHEMIC SYNDROME (OIS) Globally poor ocular perfusion, usually from high-grade carotid stenosis (usually >90% on duplex ultrasound) or chronic ophthalmic artery occlusion. The disease is usually related to atherosclerosis, but it also may be from Eisenmenger’s syndrome, carotid dissection, GCA, or other inflammatory vasculitide. Age is usually >55, and is bilateral in 20%.

Signs and symptoms: gradual decreased VA or amaurosis, ocular angina, or prolonged recovery after bright light. May present with limbal flush, AC cell (20%), NVI (two thirds of patients), or NVA or NVG (although usually has decreased IOP early secondary to decreased ciliary body perfusion), retinal artery narrowing, dilated but not tortuous veins, dot-blot midperipheral hemorrhages or microaneurysms, NVD, or CME (hypoxic capillary endothelial cells leak).

FA demonstrates delayed filling characterized by decreased arteriovenous transit time (in 95% of patients), delayed mid or laminar phase, last vein to fill >15 seconds, delayed choroidal filling (60% of patients), prominent vascular staining (95%), or CME. Ophthalmodynamometry shows decreased central retinal artery perfusion; ERG may show decreased A and B waves.

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280 RETINA AND VITREOUS

Complications: marker for vascular disease: 50% of patients have ischemic cardiovascular disease, 25% history of stroke, 20% peripheral vascular disease, increased stroke rate; overall, a 5-year mortality of 40%. If NVI is present, 90% are blind within 1 year.

Treatment: PRP for NVI is effective in 35% of patients, as well as carotid endarterectomy (CEA), unless the vessel is 100% occluded. Note: CEA may suddenly increase the ciliary body perfusion and cause an increased IOP.

North American Symptomatic CEA Trial (NASCET) showed that patients with a history of amaurosis fugax, TIA, or stroke and who had a 70 to 90% carotid stenosis have a 2-year stroke rate of 9% after CEA versus 26% in control patients who were treated only with antiplatelet therapy.

OPHTHALMIC ARTERY OBSTRUCTION Abrupt, severe vision loss (may be NLP), with a lower IOP, and intense inner and outer retinal whitening with no cherry red spot resolving over several weeks with RPE disturbance and severe optic atrophy. No A or B wave on the ERG. Grim visual prognosis.

Saturday night retinopathy: prolonged prone position with pressure on the globe that causes decreased ophthalmic artery perfusion. So named because patients may awake blind from a drunken stupor.

SICKLE CELL RETINOPATHY Abnormal red blood cell hemoglobin causes vascular sludging and occlusions. Hemoglobin in RBCs is normally in solution; however, with hypoxia or acidosis, the abnormal hemoglobin molecules become inflexible and precipate as rods within the red blood cells. The sickled, deformed RBCs then block arterioles. The most severe eye disease is seen with SC (homozygote for Hgb-C) and sickle cell thalassemia (Sthal) because the anemia is milder, thus causing more viscous blood and more vaso-occlusions. However, more severe systemic disease with homozygous sickle cell (Hgb SS) disease characterized by sickle cell ‘‘crises’’ with severe pain from microvascular occlusions, bone infarcts, leg ulcers, and autoinfarction of the spleen (susceptible to bacterial infections). Disease usually presents at age 30 to 40 years, especially in African-American patients; diagnose with hemoglobin electrophoresis.

Ten percent of African-Americans have abnormal hemoglobin: 8.5% have sickle cell trait (AS), 2.5% Hgb-C trait (AC), 0.4% homozygous sickle cell disease (SC), 0.2% sickle cell Hgb-C (SC), and 0.03% sickle cell thalassemia (Sthal).

Hemoglobin is comprised of two alpha and two beta chains. In sickle cell anemia, or S disease, a single amino acid substitution (valine for glutamic acid) in the sixth position of the hemoglobin beta chain causes an abnormal hemoglobin molecule (Hgb-S). Homozygotes have 85 to 95% Hgb-S and severe anemia (SS

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disease), whereas heterozygotes (sickle cell trait, AS disease) have 40 to 45% Hgb-S and the rest is normal hemoglobin.

Another mutation, substituting lysine for glutamic acid in the sixth position, causes sickle cell C disease (Hgb-C). Homozygotes have SC disease, and heterozygotes are considered to have sickle cell C trait (AC disease).

The thalassemias are a group of inherited disorders of hemoglobin metabolism in which there is a decrease in the net synthesis of a particular globin chain without a change in its structure.

Nonproliferative retinopathy: characterized by arteriovenous tortuosity from peripheral vascular shunting, retinal hemorrhages in any layer. Subretinal hemorrhage may have a ‘‘salmon patch’’ appearance that is >1 DD and may resolve with black chorioretinal scars from RPE hypertrophy (‘‘sunbursts’’) or intraretinal hemosiderin seen as iridescent spots. May also see ‘‘wedge sign’’ from arteriolar occlusions (usually SS disease) or ‘‘depression sign’’ from focal retinal thinning. Also associated with CRAO (especially in hyphema patients), choroidal occlusion, ‘‘sickle disk’’ sign (red spot on retinal surface), and angioid streaks (risk of CNVM). On the rest of the eye exam, patients may have conjunctiva sickle sign (comma-shaped capillaries) and iris atrophy, and are prone to hyphema.

Proliferative retinopathy: neovascularization is usually peripheral and in a classic ‘‘seafan’’ pattern. NV may lead to vitreous hemorrhage and tractional RD. Staged like retinopathy of prematurity: I (peripheral occlusions), II (AV anastamosis), III (‘‘seafans’’), IV (VH), and V (RD).

Treat with segmental PRP in the anterior periphery of the areas with capillary nonperfusion. ‘‘Seafans’’ often autoinfarct; thus, follow closely. RD usually requires vitrectomy; avoid buckles, as they increase anterior ischemia.

SUPRACHOROIDAL ARTERIAL HEMORRHAGE Rupture of arteriole (usually atherosclerotic and hardened) as it passes from the sclera into the choroid, usually from sudden hypotony (e.g., surgery or penetrating injury). Hemorrhage fills the suprachoroidal space, creating a hemorrhagic choroidal detachment, and may be expulsive, with the loss of intraocular contents and pain from globe expansion. Risk factors include age, atherosclerosis, hypotony, hypertension, chronic glaucoma, axial length >26 mm, and tachycardia.

VITREOUS HEMORRHAGE (VH) From many causes; may resolve with complications such as ocher membrane that may mimic RD, organization with fibroblast recruitment and contraction leading to tractional RD, cyclitic membrane on the anterior hyaloid face with traction on the ciliary body and hypotony, or ERM from glial cell proliferation. See Signs and Symptoms section for list of etiologies.

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