Beyond the Eye

Retinal dysfunction caused by systemic hypertension endorses cardiologist's warning

SYSTEMIC hypertension is defined as persistent high blood pressure (140 mm Hg or more for systolic pressure and 90 mm Hg or more for diastolic). It is a common affliction of Western societies and the most common disease of heart and blood vessels. It is a major cause of heart failure, stroke and renal disease.

Primary or essential hypertension does not have any identifiable cause and comprises 90% of all cases. Secondary hypertension has an underlying culprit, mainly aldosteronism, renal pathology or an adrenal medulla tumour such as a pheochromocytoma.

Untreated systemic hypertension causes damage to many organs, but heart, kidney and brain are the three most affected. The heart works against a higher pressure, and the overload may lead to angina and myocardial infarction.
Renal arterioles take the increased pressure badly; they thicken, stenosis develops and blood supply to the kidney is reduced. This results in increased secretion of renin which in turn increases blood pressure.

Hypertension also affects arterial walls, contributing to the development of arteriosclerosis and raising the likelihood of myocardial infarction and stroke. Cerebral arteries are particularly susceptible.

How hypertension damages the eye
Systemic hypertension has an effect on ocular micro-circulation; retinal, choroidal and optic nerve blood supply can be affected.
Retinal changes vary according to the severity and duration of the hypertension. The most common findings are:

• cotton-wool spots (ischaemic infarction of superficial retina)
• intraretinal haemorrhages
• generalised narrowing of arterioles
• generalised sclerosis
• tortuosity of arterioles
• arteriolar sclerotic vacuolar changes
• exudates resulting from abnormal vascular permeability, generally grey or silver
• swelling of the optic disc

Although there is not a straight-forward relationship, alterations of intraocular pressure (IOP) should also be discarded in patients with systemic hypertension.

What can be done
The aim of therapy is to control and reduce blood pressure. The reduction must be done in a controlled manner; a sudden drop in tissue perfusion can be seriously damaging, especially to the optic nerve.

A range of drug therapies are available to treat the underlying systemic hypertension, including:

• diuretics (reduce blood volume)
• angiotensin converting enzyme inhibitors (block the formation of angiotensin II promoting vasodilatation and liberation of aldosterone)
• beta-blockers (inhibit secretion of renin and decrease heart rate)
• vasodilators (relax smooth muscle in arterial walls)
• calcium channel blockers (reduce heart work, although their benefits are debated)
• alpha-blockers (block alpha adrenoreceptors)
• angiotensin II receptor antagonists (more specific than ACE inhibitors, with fewer side-effects).

Other pharmacological measures to reduce cardiovascular risk are aspirin (to reduce myocardial infarction and stroke) and statins (when total serum cholesterol is elevated).
In addition, ophthalmologists should be aware of some ocular side-effects of anti-hypertensive treatments. For example, thiazide diuretics may occasionally cause disturbance of colour vision and are photosensitive - they can potentially interfere with ocular photodynamic therapy.

Temporary hypotension may occur in elderly patients treated for hypertension, especially when supine. These periods of hypotension may led to further damage in patients with glaucoma.

Although the ophthalmologists should refer a patient with hypertension to a specialist for evaluation and drug therapy, he can recommend a series of lifestyle changes which have proven effective in managing hypertension:

• Lose weight (even a small loss helps)
• Increase the level of physical exercise
• Stop smoking
• Limit alcohol intake
• Have a healthy diet
• Manage stress

These are attitudinal changes for a pain-free disease. Hypertension can be - indeed it generally is - symptom-free at initial stages. If told their sight is in danger, many patients who would usually rather unwisely ignore cardiologists' warnings may take the recommendations more seriously.

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