Among our senses, vision is our primary sensory system which we use most. With it, we experience the outside world-we see people, houses, cars, water, mountains, trees, flowers, animals and we also see ourselves in a mirror. Our vision is highly developed and extremely efficient. We can quickly determine the nature of an object we see, its distance and movement and within a split second recognize the gender, age, familiarity and expression of a face. Vision is essential and indispensable to many parts of our daily lives, our work, free time or pleasures. Vision consists of the complex combination of visual acuity, color sense, the ability to distinguish contrasts, and ability to evaluate the location of objects in the environment (space). Most older people experience normal changes in their eyes that are associated with the aging process. In addition, there are four age related eye conditions that may result in visual impairment. In general, environmental conditions such as adequate lighting, elimination of glare, and the use of color contrast are more significant for the visual functioning of older persons than of younger persons. Many of these helpful environmental modifications are minor and inexpensive; they can be made quite easy within the homes of older persons who are visually impaired, as well as in public environments. Demonstration of human eye is given below:

Hyperopia, also known as farsightedness, long-sightedness or hypermetropia, is a defect of eye as the light is focuses at a point behind the retina not on the retina of the eye. Here, the victim can see distance object but near vision is difficult and causes strain. Hence hypermetropic people are called long-sighted.

Convex lens is used to rectify the vision or improve the vision. These lens converges rays of light which are traveling parallel to its principal axis meet at the focus. They produce real images. The lens of human eye is a double convex lens.

Myopia or Near sightedness is a deficiency of an eye, mostly due to error occurs with the focal length of the lens of the human eye. Here the victim is able to see near objects but far objects appear blurred.This disorder is when light entering the eye is focused incorrectly, making distant objects appear blurred.
Figure show an eye with such deficiency receiving light rays from a far off object. Due to the deficiency, the rays get focused ahead of the retina (the screen) and hence the eye is unable to perceive the object clearly.

Concave lens is used to reduce this defect. It diverges the incoming rays to the required extent such that the eye lens is able to focus the diverged rays right on the retina. These lenses produce only virtual images. A virtual image is one from which light rays only appear to come.