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Hypertension and hypertensive retinopathy

Accreditation Number: ODO xxx/xx/01/2020

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Introduction

Hypertension, which is synonymous with high blood pressure, is a common medical condition in which the long-term force of the blood against the arterial walls is high enough that it may eventually cause health problems. It is important because of the increased risk of developing heart disease, cerebrovascular accident (commonly referred to as stroke), kidney disease, hypertensive retinopathy, and sometimes death. An estimated 1.13 billion people worldwide have hypertension, most (two-thirds) living in low- and middle-income countries. This is due mainly to a rise in hypertension risk factors in these populations, with 1 in 4 men and 1 in 5 women having hypertension.  Hypertensive retinopathy includes two disease processes: the acute effects of systemic arterial hypertension as a result of vasospasm and the chronic effects of hypertension caused by arteriosclerosis. Both these predispose patients to visual loss from vascular occlusions and macroaneurysms.

Hypertension diagnosis

Blood pressure is determined both by the amount of blood the heart pumps and the amount of resistance to blood flow in the arteries. The more blood the heart pumps and the narrower the arteries, the higher the blood pressure. Blood pressure is written as two numbers. The first (systolic) number represents the pressure in blood vessels when the heart contracts or beats. The second (diastolic) number represents the pressure in the vessels when the heart rests between beats.

The diagnosis of hypertension is made, when it is measured on two different days, the systolic blood pressure readings on both days is ≥140 mmHg and/or the diastolic blood pressure readings on both days is ≥90 mmHg. The exception to this rule is when malignant hypertension (hypertensive emergency) is present even on a single event, which is considered a medical emergency and occurs when the systolic reading exceeds 180mm Hg and/or the diastolic number exceeds 110mm Hg.

Hypertension risk factors

Modifiable risk factors include:

  • Being overweight or obese.The more one weighs, the more blood one needs to supply oxygen and nutrients to the tissues. As the volume of blood circulated through the blood vessels increases, so does the pressure on the arterial walls.
  • Physical inactivity.People who are sedentary and inactive tend to have higher heart rates. The higher the heart rate, the harder the heart must work with each contraction, and the stronger the force on the arteries. Lack of physical activity also increases the risk of being overweight.
  • Using tobacco-related products.Not only does smoking or chewing tobacco immediately raise blood pressure temporarily, but the chemicals in tobacco can damage the lining of the artery walls. This can cause the arteries to narrow and increase the risk of heart disease. Secondhand smoke also can increase heart disease risk.
  • Unbalanced diet. A diet high in saturated fat and trans fats, low intake of fruits and vegetables is unhealthy.
  • Too much salt (sodium) in the diet.Too much sodium in the diet can cause the body to retain fluid, which increases blood pressure.
  • Too little potassium in the diet.Potassium helps balance the amount of sodium in the cells. Insufficient potassium in the diet or inadequate retention of potassium may lead to the accumulation of too much sodium in the blood.
  • Alcohol abuse.Over time, heavy drinking can damage the heart. Having more than one drink a day for women, and more than two drinks a day for men may affect blood pressure.
  • High levels of stress can lead to a temporary increase in blood pressure.
  • Certain chronic conditions.Certain co-existing chronic conditions also may increase the risk of high blood pressure, such as kidney disease, diabetes, and sleep apnea.

Non-modifiable risk factors include:

  • The risk of hypertension increases with age. Until about age 64, high blood pressure is more common in men. Women are more likely to develop high blood pressure after age 65.
  • High blood pressure is particularly prevalent among people of African descent, often developing at an earlier age than it does in whites. Serious complications, such as stroke, heart attack and kidney failure, also are more common in people of African heritage.
  • Family history.High blood pressure tends to run in families.

Hypertension signs and symptoms

Hypertension is called a “silent killer”. Most people with hypertension are unaware that they have the disease and may have no warning signs or symptoms. For this reason, it is essential that blood pressure is measured regularly. When symptoms do occur, they can include early morning headaches, nosebleeds, irregular heart rhythms, vision changes, and buzzing in the ears. Severe hypertension can cause fatigue, nausea, vomiting, confusion, anxiety, chest pain, and muscle tremors.

Complications of uncontrolled hypertension

The excessive pressure on the artery walls caused by high blood pressure can damage the blood vessels, as well as organs in the body. The higher the blood pressure and the longer it goes uncontrolled, the greater the damage. Uncontrolled high blood pressure can lead to complications, including:

  • Angina. Angina is a type of chest pain caused by reduced blood flow to the heart. It is a symptom of coronary artery disease often described as squeezing, pressure, heaviness, tightness, or pain in the chest.
  • Heart attack or stroke.High blood pressure can cause hardening and thickening of the arteries (atherosclerosis). Subsequently, the blood supply to the heart is blocked, and heart muscle cells die from lack of oxygen, which can lead to a heart attack, stroke, or other complications. The longer the blood flow is blocked, the greater the damage to the heart.
  • Increased blood pressure can cause the blood vessels to weaken and bulge, forming an aneurysm. If an aneurysm ruptures, it can be life-threatening.Heart failure. To pump blood against the higher pressure in the vessels, the heart has to work harder. This causes the walls of the heart’s pumping chamber to thicken (left ventricular hypertrophy). Eventually, the thickened muscle may have a difficult time pumping enough blood to meet the body’s needs and vital organs, which can lead to heart failure.
  • Irregular heartbeat. An irregular heartbeat can lead to sudden death.
  • Weakened and narrowed blood vessels in the kidneys.This can prevent these organs from functioning normally.
  • Thickened, narrowed, or torn blood vessels in the eyes.This can result in vision loss.
  • Metabolic syndrome.This syndrome is a cluster of disorders of the body’s metabolism, including increased waist circumference, high triglycerides; reduced high-density lipoprotein (HDL) cholesterol (the “good” cholesterol); high blood pressure and high insulin levels. These conditions make one more likely to develop diabetes, heart disease, and stroke.
  • Trouble with memory or understanding.Uncontrolled high blood pressure may also affect the ability to think, remember, and learn. 
  • Dementia. Narrowed or blocked arteries can limit blood flow to the brain, leading to a certain type of dementia (vascular dementia).

Management of hypertension

Reducing hypertension prevents heart attack, stroke, and kidney damage, as well as other health problems.

Hypertension prevention strategies include:

  • Reducing salt intake (to less than 5g daily)
  • Eating more fruit and vegetables
  • Being physically active on a regular basis
  • Avoiding the use of tobacco and related products
  • Reducing alcohol consumption
  • Limiting the intake of foods high in saturated fats
  • Eliminating/reducing trans fats in the diet
  • Reducing and managing mental stress
  • Regularly checking blood pressure
  • Treating high blood pressure
  • Managing other medical conditions

The physical examination of a patient with hypertension includes vital signs (pulse rate, temperature, respiration rate, and blood pressure), cardiovascular examination, pulmonary examination, neurological examination, and dilated fundoscopy. Key elements of the cardiovascular examination include heart sounds (gallops or murmurs), carotid or renal bruits, and peripheral pulses. A pulmonary examination can identify signs of heart failure if rales are present. Signs of cerebral ischaemia can be detected by a good neurological examination. The dilated fundoscopic examination is necessary for the staging of hypertensive retinopathy. Drugs that are commonly used to reduce blood pressure include angiotensin-converting enzyme inhibitors, calcium channel blockers, and diuretics. Other less commonly used medications include α-adrenergic blockers, direct vasodilators, and central α2-adrenergic agonists. Follow up is dependent upon the degree of hypertension and resistance to medications.

Pathophysiology of hypertensive retinopathy

Retinal haemorrhages develop when necrotic vessels bleed into either the nerve fibre layer causing “flame-shaped” haemorrhages or the inner retina causing “dot and blot” haemorrhages. Cotton wool spots are caused by ischaemia to the nerve fibre layer secondary to fibrinous necrosis and luminal narrowing. Ischaemia to the nerve fibres leads to decreased axoplasmic flow, nerve swelling, and, ultimately fluffy opacification. Exudates occur later in the course of disease, surrounding areas of haemorrhage, as a result of lipid accumulation. Papilloedema is a result of both leakage and ischaemia of arterioles supplying the optic disc that undergo fibrinous necrosis. Ischaemia causes optic nerve swelling and blurred disc margins, while leakage causes haemorrhage and disc oedema.

Hypertensive retinopathy diagnosis

Hypertensive retinopathy diagnosis is based upon its clinical appearance on the dilated fundoscopic exam and coexistent hypertension. The case history should focus upon hypertension disease history, symptoms of hypertension, and history of its complications. To ascertain hypertension disease severity, patients should be asked about the duration of hypertension, medications taken as well as compliance. Symptoms of hypertension to enquire about include headaches, eye pain, reduced visual acuity, focal neurological deficits, chest pain, shortness of breath, dyspnea on exertion, paroxysmal nocturnal dyspnea, orthopnea, and palpitations.

Signs and symptoms of hypertensive retinopathy

The signs of malignant hypertensive retinopathy include constricted and tortuous arterioles, retinal haemorrhages, hard exudates, cotton wool spots, retinal oedema, and papilloedema. The signs of chronic arterial hypertension in the retina include widening of the arteriole reflex, arteriovenous crossing signs, and copper or silver wire arterioles (copper or silver coloured arteriole light reflex). Poor perfusion of the choriocapillaris causes Elschnig spots, defined as hyperpigmented patches in the choroid surrounded by a ring of hypopigmentation. Siegrist streaks can also be found, defined as linear hyperpigmented lesions over choroidal arteries. Hypertensive choroidopathy can cause a focal pigment epithelium detachment, leading to exudative retinal detachment. Hypertension may lead to optic neuropathy. The signs of optic neuropathy include “flame-shaped” haemorrhages at the disc margin, blurred disc margins, congested retinal veins, papilloedema, and secondary macular exudates. Acute malignant hypertension will cause patients to complain of eye pain, headaches, or reduced visual acuity. Chronic arteriosclerotic changes from hypertension will not cause any symptoms alone. However, the complications of arteriosclerotic hypertensive changes will cause patients to present with the typical symptoms of vascular occlusions or macroaneurysms.

The signs of malignant hypertension are summarised by the Modified Scheie Classification of Hypertensive Retinopathy:

Grade 0: No changes

Grade 1: Barely detectable arterial narrowing

Grade 2: Obvious arterial narrowing with focal irregularities

Grade 3: Grade 2 plus retinal haemorrhages, exudates, cotton wool spots, or retinal oedema

Grade 4: Grade 3 plus papilloedema

The signs of chronic arteriosclerotic hypertension are summarised by the Scheie Classification.

Stage 1: Widening of the arteriole reflex

Stage 2: Arteriovenous (A/V) crossing sign

Stage 3: Copper-wire arteries (copper-coloured arteriole light reflex)

Stage 4: Silver-wire arteries (silver-coloured arteriole light reflex)

“Flame-shaped” haemorrhages and cotton wool spots in central retinal vein occlusion is a complication of hypertensive retinopathy. P.Ramkissoon, 2020.

Complications of hypertensive retinopathy

Hypertension predisposes patients to many other retinal vascular diseases, including central or branch retinal artery occlusion, central or branch retinal vein occlusion, and retinal arterial macroaneurysms. Ischaemia secondary to vascular occlusions can cause neovascularisation, vitreous haemorrhage, epiretinal membrane (ERM) formation, and tractional retinal detachment. Hypertension also leads to more advanced diabetic retinopathy progression. Hypertensive optic neuropathy can cause chronic papilloedema, leading to optic nerve atrophy and severe loss of visual acuity. Patients with severe hypertensive retinopathy and arteriosclerotic changes are at increased risk for coronary disease, peripheral vascular disease and stroke. Since arteriosclerotic changes in the retina do not regress, these patients remain at increased risk for retinal artery occlusions, retinal vein occlusions, and retinal macroaneurysms. Most retinal changes secondary to malignant hypertension will improve once blood pressure is controlled. Damage to the optic nerve and macula, however, could cause long term reductions in visual acuity.

Management of hypertensive retinopathy

The treatment for hypertensive retinopathy is primarily focused upon reducing blood pressure. Fluorescein angiography (FA) during acute malignant hypertension will demonstrate retinal capillary non-perfusion, microaneursym formation, and a dendritic pattern of choroidal filling in the early phase. In the late phase, diffuse leakage will be seen. Indocyanine green angiography during malignant hypertension will show a “moth-eaten” appearance of the choriocapillaris. Fluorescein angiography can demonstrate hypertensive choroidopathy. FA will show focal choroidal hypoperfusion in the early phases and subretinal leakage in the later phases.

The treatment for malignant hypertensive retinopathy is to reduce the systemic blood pressure below 140/90 mmHg. This can be accomplished by any of the armamentarium of medical treatments for hypertension. Medical treatment can only treat the acute changes in hypertension from vasospasm and vascular leakage. There is no treatment for arteriosclerotic changes of chronic hypertension. Close collaboration is essential between the eye care practitioner and the primary care physician for consistent follow up individually tailored to each patient.

Clinical pearls

  • Hypertension (HTN) is a major factor in cardiovascular disease because it puts added strain on the heart and vasculature. It also is linked to myocardial infarctions (MI) and cerebrovascular accidents (CVA). Further, the stress caused by HTN on the various organs can result in significant damage and even renal failure, especially in the hypertensive emergency phase.
  • Common hypertensive retinal changes are “flame-shaped” haemorrhages in the superficial layers of the retina and cotton-wool patches caused by occlusion of the precapillary arterioles with ischaemic infarction of the inner retina. Long-standing hypertension can produce arteriolar sclerotic vascular changes, such as copper or silver wiring of the arterioles, or arteriovenous nicking. Another sign of chronic hypertension is lipid exudates resulting from abnormal vascular permeability.
  • Swelling of the optic disc is an ominous sign, seen as blurring of the disc margins. This is the hallmark of malignant hypertension, which carries a poor prognosis for the patient’s health if left untreated. BP must be emergently controlled to decrease the risk of developing heart and renal failure and hypertensive encephalopathy as well as stroke and permanent vision loss.

Conclusion

Hypertension is a major cause of premature death worldwide. The physical examination of a patient with hypertension must include vital signs, cardiovascular examination, pulmonary examination, neurological examination, and dilated fundoscopy. The primary prevention of hypertensive retinopathy is routine blood pressure monitoring and treatment.

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