Matters of the eye

Hello again,

Right now you are reading the words in this newspaper with both your eyes.

You have your eyes pointed at these words and all you are really aware of is the newspaper page that you see. Now, if someone were to sneak up behind you and slowly come around to your side, you would probably see the person move and know he or she was there.{{more}}

But how could you see someone off to the side of you if your eyes are looking straight at this page? It’s because you are using your peripheral (side vision) which accounts for a large percentage of your whole visual field. Your visual field is all you can see at one time without turning your head. A normal visual field extends around 170 degrees, although certain conditions such as glaucoma, brain tumours, cataracts, retinal and optic nerve disease can cause it to be narrower. In fact, one of the definitions of legal blindness is a visual field less than 20 degrees.

Half of the inside of your eye is lined with retinal tissue. When you look straight at an object, you line up that object with what we call the macula, a tiny one square millimetre area of the retina that gives you the sharpest vision possible. So there’s a whole lot of retina that isn’t completely tuned into where you are looking. But when people come up beside you they move enough to alert the rest of your retina that something is happening out there. Peripheral vision is very important when you’re driving a car for example because you’re using your side vision to glimpse the cars on either side of you without actually turning your head or your eyes completely to the side. A defect in your peripheral vision is called a blind spot.

Next week we will discuss how to roughly test your peripheral vision by yourself. If you want to know how the peripheral vision is accurately tested, you need to do what we call a visual field test, which is a very sophisticated eye examination that tests thousands of different points on your retina for subtle blind spots and to see if the retina is picking up what it should be picking up.

So, until then….have a great weekend.

Dr Kenneth Onu is a resident Consultant Ophthalmologist at the Beachmont Eye Institute/Eyes R Us Send questions to: Beachmont@gmail.com

Tel: 784 456-1210