The image shows that in myopia the image fall short of the retina when the target object is far away.
CONCAVE LENS FOR NEARSIGHTEDNESS
A concave lens is a diverging lens which works similar to the convex mirror. This lens is thicker towards the edges and thin in the middle and is used in helping correction of nearsightedness. All images produced by concave lenses are virtual, erect and reduced.
Hypermetropia also known as hyperopia or farsightedness is another type of eye defects. Hyperopia is the opposite of myopia means that a person who is suffering from this disease able to see objects far from the eye visibly. In this case the eye is shorter than normal and the image focuses behind the retina this means it doesn’t focus even when it reaches retina. The images focus at the back of the retina.
CONVEX LENS FOR FARSIGHTEDNESS
A convex lens is a converging lens which works much like a concave mirror. This kind of lens is thicker in the middle and thinner towards the edges, like the lens in a magnifying glass. The image is changed by the position of the object in relation to the focal length and the radius of curvature. This lens helps people who are suffering from farsightedness.
The power of a lens with focal length f is P=1/f where lens power is measured in dioptres, D. The distances between the image and the source are related to each other by the lens equation:
1/V = 1/U + 1/F
Where U = object distance
V = image distance
F = focal length
In this equation the term f is a permanent number, called the focal length of the lens. It tells everything about the lens itself, including the material it is made from and the curvature of the surfaces.
Checking people’s health is very important. Each defects of eye has different needs of lens with different focal length or point. Ensuring that people can see as well as possible is a very useful contribution to their health. By correcting the lens of an eye people will able to see clearly vision.
Limitations
It is not always possible to balance red and purple vision, as red light has different wavelength, different wave speed in different mediums and different refractive index than the green light.
Sources
- Salters Horners Advanced Physics (ISBN: 978-1-40589-6023)
- Information about defects of eye Virtualsciencefair.org/2005/dong5a0/public_html (February 12 2009)
- librarythingquest.org/C006027/html_ver/mis_def.html (February 6 2009)
- Notes from class.
