Accommodation The term 'accommodation' is used to indicate the ability of the eye to change its focus, and thus get a clear image on the retina. The gradual decline in accommodation is called presbyopia, and is inevitable with age. Simple refractive errors Myopia, or short-sightedness, is when the image is focussed in front of the retina. Good vision can be obtained by correction with concave lenses in spectacles or contact lenses. Hypermetropia, or long-sightedness, is when the image is focussed behind the retina.
Convex lenses give good vision.
Astigmatism literally means without point focus. Presbyopia commonly occurs after the age of 40, and bifocal or varifocal spectacles are often required. Multifocal spectacles may necessitate the user moving their head to get a focussed image, and thus the task may take longer. It is particularly common among older people. The macula is at the centre of the retina and is used for detailed activities such as reading and recognising faces, and is used to detect colours.