We must keep an eye on our vision.
The eyes are described poetically as a window to your soul.
And medically speaking, the eyes are the window to the body. It's only through your eyes that a doctor can view some of your vital internal organs.
Using an ophthalmoscope, a doctor can examine arteries on the retina at the back of the eye and see signs of high blood pressure and arteries hardening.
If these retinal arteries are furred up, then so are the rest of the arteries in your body - useful for a doctor to know.
The eye is also the brain's window on the world, focusing light on the retina, which converts images into nerve impulses, which are then transmitted to the back of the brain for vision.
h The retina needs a supply of oxygen-rich blood, and if anything interferes with it then your vision could be in jeopardy.
Two things can happen to the retina to compromise your eyesight: blockage of the retinal vein and retinal detachment. Both can occur at any age but get more common as we age.
A block in the retinal vein, which drains the eye, is a common cause of sudden, painless blindness in older people. In fact, one or two people in 100 who are older than 40 will experience it, often due to undiagnosed and untreated high blood pressure, another reason to get checked.
But other risk factors that we can all minimise include raised cholesterol, smoking, diabetes and obesity.
How much vision you lose depends on the size of the vein and how much of your retina is affected.
As long as you see your doctor urgently, much of your sight can be saved.
Tests can reveal that only a branch of the main retinal vein is blocked and the future will look bright because half of the cases get better in six months. If treatment is needed, most respond to laser therapy.
Meanwhile retinal detachment is rare but more likely to cause permanent blindness if not treated promptly.
You could be lucky if symptoms alert you to imminent detachment, like floaters, spots or strings before your eyes, flashing lights even when your eyes are closed, or a shadow over part of your visual field.
The simplest treatment is pneumatic retinopexy, where a bubble of gas is injected into the eye and presses the retina back in place. The break is then permanently sealed with a laser.
If your vision ever clouds over, always make an appointment to see your doctor.