Questionnaire: How Well Do You Know Your Eyes?
The eyes are said to be the window to the soul, but how well do you know about this important gateway? Try answering this short set of questions, and check out the answers to find out more about your eyes.
Q1. What Machine is Most like an Eye?Probably the answer that most people would give is – a camera. Modern day cameras are more sophisticated than the original pin-hole cameras first introduced a couple of hundred years ago, but they still work on the same principle. Like an eye, a camera has a lens, an aperture (similar to the pupil of the eye) and light is focused on a surface that detects light. In the case of a camera, this can be film, or today, more usually a digital processing interface, while the eye has the retina with its photoreceptor cells.
Q2. How many layers does the cornea have?The cornea is the covering to the front of the eye. It is completely transparent and you might think its design is simple – but it actually has five layers. It is the first lens of the eye – not the main one, but it does act to focus light rays into the eye. On the outside is a five—cell layer called the epithelium, followed by the Bowman’s layer, an elastic, fibre-like covering which separates the epithelium from the stromal layer, which is mainly collagen. Under that is the endothelium, which is only one cell thick. The final layer, which is the inner elastic layer of the cornea that separates it from the fluid of the anterior chamber of the eye is called Descemet’s membrane.
Q3. What is the Real Function of Tears?Tears are thought to be all about emotion and feelings but, in fact they are a physiological fluid that prevents bugs, pollution and dust affecting the delicate outer surface of the cornea. No-one actually knows why we cry when we are upset but it’s not thought to be related to the threat of infection or pollution...
Q4. What are the Two Eye Chambers?The first one, the one just beyond the cornea, is called the anterior chamber because that is the one at the front of the eye. The inner chamber, between the lens and the retina is called the posterior chamber; this forms the main cavity of the eye ball and is filled with a fluid called the vitreous humour.
Q5. What is the choroid?This is a thin sheet between the outside of the eyeball, the sclera, and the inner, sensitive surface of the retina. The choroid is packed with tiny blood vessels and these are responsible for taking oxygen and nutrients into the photoreceptor cells and taking away the waste metabolites and carbon dioxide. A good blood supply keeps the retina working well and the eyesight healthy.
Q6. What is the ciliary body?This strangely named structure is a ridged area at the front of the eye that attaches the ciliary muscles. These are tiny muscles but they do an important job – they control the lens of the eye so that we can change our focus from objects in the far away distance to objects just in front of our nose. This ability to change focus is called accommodation and as the lens hardens with age, it becomes harder to do. This is why people at the age of about 45 need reading glasses, bifocals or varifocals.
Q7. What are the Photoreceptors?
These are the light sensitive nerve cells that line the back of the retina and allow us to see. There are two types – rods and cones – the former ‘sees’ in black and white only; the cones are responsible for our colour vision. Most of the cones are concentrated in the central area of the retina, the macula, and its epicentre, the fovea.
Q8. What is the Blind Spot
The blind spot is the small area on the retina that does not have either rods or cones. The reason for this is that this is the point where the optic nerve and the main artery and vein that supply the retina leave the eyeball and go to either the brain or the main blood system.