Hypertensive retinopathy refers to fundus changes occurring in patients suffering from systemic hypertension. Although the term hypertensive retinopathy implies only retinal changes but in fact the clinical presentation includes changes of hypertensive:
- Choroidopathy, and
- Optic neuropathy
Pathogenesis of Hypertensive Retinopathy
Three factors which play role in the pathogenesis of hypertensive retinopathy are vasoconstriction, arteriosclerosis and increased vascular permeability.
1. Vasoconstriction: Arteriolar narrowing is the primary response to raised blood pressure and is related to the severity of hypertension.
- Retinal arterioles’s vasoconstriction occurs in pure form in young individuals, but is affected by the pre-existing involutional sclerosis in older patients.
- Vasoconstriction of choroidal vessels causes choroidal and RPE ischaemia, which manifests as hypertensive choroidopathy.
- Vasoconstriction of peripapillary choroid leads to optic nerve head ischaemia, manifesting as hypertensive optic neuropathy.
2. Arteriosclerotic changes which manifest as changes in the arteriolar reflex and A-V nipping result from thickening of the vessel wall and are a reflection of the duration of hypertension. In older patients arteriosclerotic changes may pre-exist due to involutional sclerosis.
3. Increased vascular permeability results from hypoxia and is responsible for haemorrhages, exudates, focal retinal oedema, macular oedema, focal intraretinal periarterial transudates (FIPTs), and disc oedema.
Clinically, the hypertensive fundus changes can be described as:
- Chronic hypertensive retinopathy, and
- Malignant or acute hypertensive retinopathy.
Chronic hypertensive retinopathy
Patients with chronic hypertensive retinopathy are usually asymptomatic. Clinical situations in which chronic hypertensive retinopathy occurs include:
1. Hypertension with involutionary (senile) sclerosis
When hypertension occurs in elderly patients (after the age of 50 years) in the presence of involutionary sclerosis the fundus changes comprise augmented arteriosclerotic retinopathy.
2. Chronic hypertension with compensatory arteriolar sclerosis
This condition is seen in young patients with prolonged benign hypertension usually associated with benign nephrosclerosis. The young arterioles respond by proliferative and fibrous changes in the media (compensatory arteriolar sclerosis). Advanced fundus changes in these patients have been described as ‘albuminuric or renal retinopathy
Fundus changes of chronic hypertensive retinopathy can be summarized as below:
1. Generalized arterial narrowing:
Generalized arterial narrowing or attenuation depending upon the severity of hypertension may be mild or marked, and consists of vasoconstrictive and sclerotic phases.
- Vasoconstrictive phase occurs due to diffuse vasospasm which manifests when a significant elevation of blood pressure has persisted for an appreciable period and is characterised by an increase in retinal arteriolar tone.
- Sclerotic phase occurs due to intimal thickening. hypoplasia of tunica media, and hyaline degeneration; and is characterised by arteriolar narrowing associated with tortuosity.
2. Focal arteriolar narrowing
It is seen as areas of localized vasoconstriction on the disc and within ½ disc diameter of its margin zone.
3. Arteriovenous nicking
It is the hallmark of hypertensive retinopathy and occurs where arteriole crosses and compresses the vein, as the vessels share a common adventitious sheath. Also known as A-V crossing changes, these include:
- Salu’s sign, i.e., deflection of veins at the arteriovenous crossings,
- Bonnet sign, i.e., banking of veins distal to arteriovenous crossings, and
- Gunn sign, i.e., tapering of veins on either side of the crossings.
4. Arteriolar reflex changes.
The normal light reflex of the retinal vasculature is formed by the reflection from the interface between the blood column and vessel wall.
- Bright and thin, linear blood reflex is seen normally over the surface of the arteriole in the young age and is predominantly because of blood column in the arteriole, since the vessel wall is by and large transparent.
- More diffuse and less bright reflex is seen due to thickening of vessel wall and represents changes of grade I and II hypertensive retinopathy.
- Copper wiring, i.e., reddish-brown reflex of the arterioles occurs due to progressive sclerosis and hyalinization, and is a sign of grade III retinopathy.
- Silver wiring i.e., opaque-white reflex of the arterioles occurs ultimately due to the continued sclerosis, and is seen in grade IV hypertensive retinopathy.
5. Superficial retinal haemorrhages
They (flame shaped) occur at the posterior pole due to disruption of the capillaries in the retinal nerve fibre layer. These haemorrhages disappear in 3 to 5 weeks.
6. Hard exudates
They are lipid deposits in the outer plexiform layer of retina which occur following leaky capillaries in severe hypertensive retinopathy. They appear as yellowish waxy spots with sharp margins. Usually they are generally seen in posterior pole and may be arranged as macular-fan or macular-star. They are also temporary and may disappear in 3-6 weeks.
7. Cotton wool spots
They are fluffy white lesions and represent the areas of infarcts in the nerve fibre layer. These occur due to ischaemia caused by capillary obliterations in severe hypertensive retinopathy. Due to their cotton wool feathery appearance they are also termed as soft exudates (a misnomer in fact).
Malignant hypertensive retinopathy
Malignant hypertension is not a separate variety of hypertension, but is an expression of its rapid progression to a serious degree in a patient with relatively young arterioles undefended by fibrosis.
Fundus picture is characterised by changes of acute hypertensive retinopathy, choroidopathy and optic neuropathy
I. Acute hypertensive retinopathy changes include:
- Marked arteriolar narrowing due to spasm of the arteriolar wall, in response to sudden rise in blood pressure.
- Superficial retinal haemorrhages, flame shaped arranged in clusters, appear in the posterior pole area due to disruption of capillaries in the nerve fibre layer.
- Focal intraretinal periarteriolar transudates (FIPTS) are small, white, focal oval lesions occurring due to the deposition of macromolecules along the major arterioles. These result due to break down of blood-retinal barrier following dilatation of terminal arterioles as a result of sudden rise in blood pressure in malignant hypertension.
- Cotton wool spots are also more marked in malignant hypertensive retinopathy.
- Microaneurysms, shunt vessels and collaterals may e also develop as a result of capillary obliterations.
II. Acute hypertensive choroidopathy changes include:
- Acute focal retinal pigment epitheliopathy, e characterised by focal white spots, occurs due to acute ischaemic changes in choriocapillaries.
- Elschnig’s spots are small black spots surrounded by yellow halos, these are formed due to clumping and atrophy of the infarcted pigment epithelium (focal white spots) described above.
- Siegrist streaks are formed due to linear configuration of the pigment along the choroidal er arterioles. These are formed due to fibrinoid y necrosis associated with malignant hypertension.
- Serous neurosensory retinal detachment, which preferentially affects the macular area, may occur due to accumulation of fluid beneath the retina following breakdown of outer blood-retinal barrier owing to ischemic damage to the retinal pigment epithelium. It may also manifest as exudative bullous retinal detachment with shifting subretinal fluid.
III. Acute hypertensive optic neuropathy changes include:
- Disc oedema and hemorrhages on the disc and peripapillary retina which occur due to vasoconstriction of peripapillary choroidal vessels supplying the optic nerve head. The ischemia of the optic nerve head leads to stasis of axoplasmic flow, thus the lesion is a form of anterior ischaemic optic neuropathy.
- Disc pallor, of variable degree, may occur late in the course of disease.
Staging of Hypertensive Retinopathy
Several classification schemes have been described to stage hypertensive retinopathy. No classification is clinically useful. A few popular classifications, are given below, just for their historical value.
Keith and Wagner classification
- Grade I. Mild generalized arteriolar attenuation, particularly of small branches, with broadening of the arteriolar light reflex and vein concealment.
- Grade II. Marked generalized narrowing and focal attenuation of arterioles associated with deflection of veins at arteriovenous crossings (Salus’ sign).
- Grade III. Grade II changes plus copper wiring of arterioles, banking of veins distal to arteriovenous crossings (Bonnet sign), tapering of veins on either side of the crossings (Gunn sign) and right-angle deflection of veins (Salu’s sign). Flame-shaped haemorrhages, cotton-wool spots and hard exudates are also present.
- Grade IV. All changes of grade III plus silver-wiring of arterioles and papilloedema.
Staging of retinopathy changes is as follows:
- Stage 0. No visible retinal abnormalities
- Stage 1. Diffuse arteriolar narrowing; no constriction focal
- Stage 2. More pronounced arteriolar narrowing with focal constriction
- Stage 3. Focal and diffuse narrowing, with retinal haemorrhages
- Stage 4. Retinal oedema, hard exudates, optic disc edema
Grading of the light reflex changes resulting from anterio sclerosis is as follows:
- Grade 0. Normal Grade
- 1. Broadening of light reflex with minimal arteriolovenous compression
- Grade 2. Light reflex changes and arteriovenous crossing changes more prominent
- Grade 3. Copper-wire appearance and more prominent arteriolovenous compression
- Grade 4. Silver-wire appearance and severe arteriolovenous crossing changes.
Wong and McIntosh classification
It is characterised by one or more of the following signs: generalised arteriolar narrowing, focal arteriolar narrowing, AV nicking, arteriolar wall reflex broadening. There is weak associations with stroke, coronary heart disease and cardiovascular mortality.
They consists of mild retinopathy with one or more of the following signs: retinal haemorrhages (blot and dot or flame shaped) microaneurysms, cotton-wool spots, and hard exudates. There is strong association with stroke, congestive heart failure, renal dysfunction and cardiovascular mortality.
Usually, they consists of moderate retinopathy signs plus optic disc swelling, may be associated with visual loss. Associated with mortality and renal failure.
Management of Hypertensive Retinopathy
Mild hypertensive retinopathy requires blood pressure control only.
Moderate hypertensive retinopathy patients. (characterised by retinal haemorrhages, microaneurysms, and cotton-wool spots) in addition to blood pressure control benefit from further assessment of vascular risk factors (e.g., cholesterol levels) and, if indicated, risk reduction therapy (e.g., cholesterol lowering agents).
Accelerated hypertensive retinopathy characterized by bilateral disk swelling which may occur in conjunction with severe hypertension needing urgent antihypertensive management. In such instances, physicians should aim for a small stepwise control of pressure over a few hours, and avoid a sudden reduction in blood pressure which may reduce perfusion of optic nerve head and central nervous system (causing stroke).
Note: With adequate hypertension treatment, resolution of signs may occur over a period of up to a year. Thus follow-up of patients for a year may be needed.
Retinopathy in pregnancy induced hypertension
Pregnancy-induced hypertension (PIH), previously known as ‘toxaemia of pregnancy, is a disease of unknown etiology characterised by raised blood pressure, proteinuria and generalised oedema
Retinal changes are liable to occur in this condition when blood pressure rises above 160/100 mm of Hg and are marked when blood pressure rises above 200/130 mm of Hg.
- Earliest changes consist of narrowing of nasal arterioles, followed by generalised narrowing.
- Severe persistent spasm of vessels causes retinal hypoxia characterised by appearance of ‘cotton wool spots’ and superficial haemorrhages.
- Further progression of retinopathy occurs rapidly if pregnancy is allowed to continue.
- Retinal oedema and exudation is usually marked and may be associated with ‘macular star’ or flat macular detachment’ Rarely, it may be complicated by bilateral exudative retinal detachment.
- Prognosis for retinal reattachment is good, as it occurs spontaneously within a few days of termination of pregnancy.
Changes of retinopathy are reversible and disappear after the delivery, unless organic vascular disease is established.
- In preorganic stage when patient responds well to conservative treatment, the pregnancy may justifiably be continued under close observation.
- Advent of hypoxic retinopathy (cotton wool spots retinal oedema and haemorrhages), however should be considered an indication for termination of pregnancy; otherwise, permanent visual loss or even loss of life (of both mother and foetus) may occur.