What is normal vision? Come to think of it, what is vision? The majority of people consider it to be one of main senses, and in general they are almost right. But the more correct wording is that vision is a sensation or a sensory feeling. Doctors define vision as ability to percept color, light and disposition of objects in space as images. Humans and animals have optical vision though some other ways of perception also exist. Ultrasound sensation, characteristics of bats, is one of them.

Like any organ in a body eyes can fulfil their functions wrongly or not to a full extent. As a result of it, visual impairment can develop. But what is normal vision? To answer this question keep in mind that eyes are biological optical system comprising of lenses.

From the course of physics we know that each lens has focal distance. It is the distance where clear image is projected after the refraction of light rays in the lens of an object in a distance. Focal distance is a constant and it depends on the radius of lenses. For a healthy eye focal distance is equal to the distance between two lenses, it means between retina and cornea. In average it is about 23,5-24 mm. Such focal distance means that a person has normal vision. In other words, the vision is considered to be normal when the image is projected strictly on the retina of an eye bulb.

At first the light ray passes through the cornea, then through crystalline lens where it is undergoes the refraction after which it focuses on the retina. The full power of refraction is measured in dioptres. When the process of refraction is correct the image focuses on the retina discretely.

The breaches in the process of refraction lead to visual impairment. Short sight, long sight and astigmatism are among them, and these diseases are widespread. Today more than 30% of people suffer from the wrong process of refraction. Glasses have been developed to help to rectify these problems, and be they purely functional optical versions or stylish branded ones like Ray Ban sunglasses, they all help to correct vision or prevent any further deterioration.

Modern medicine reached a high level of development. That’s why in case of an early discovery, the development of the diseases can be restrained. If the visual impairment is hereditary, different methods of treatment can be applied, and regular medical consultations can be of much help. And if you are lucky not to have any problems with eyes try to stick to healthy way of life, enrich your body with vitamins and save your vision with the help of exercises and periods of resting.