Explanation
Cylindrical lens arc used for removing astigmatism.
Visible region decreases, so the depth of image will not be seen.
In short sightedness, the focal length of eye lens decreases, so image is formed before retina.
This is the defect of hypermetropia.
In short sightedness, the focal length of eye lens decreases and so the power of eye lens increases.
Colour blindness is a genetic disease and still cannot be cured.
Convexity of Lens changes by the pressure applied by ciliary muscles.
In myopia, eye ball may be elongated so, light rays focused before the retina.
Because for healthy eye image is always formed at retina.
Power of the lens given positive so defect is hypermetropia.
A bifocal lens consist of both convex and concave lenses with lower part is convex.
In microscope final image formed is enlarged which in turn increases the visual angle.
In compound microscope objective forms real image while eye piece forms virtual image.
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