In senile nuclear cataract what type of myopia is seen?
Ans. is 'b' i.e., Index myopia Nuclear changes of aging induce a modification of refractive index of lens and produce an index myopia. "Nuclear cataracts cause a general decrease in the transperancy of the lens nucleus.They are associated withindexmyopia" -- Ophthalmic study guide Causes of errors of refraction Possible causes of ametropia are : ? 1) Axial It is the commonest form of ametropia (both myopia and hypermetropia). In hypermetropia, there is an axial shoening of eyeball. So, image is formed behind the retina. In myopia, there is an axial lengthening of eyeball. So, image is formed in front of the retina. 1 mm change in axial length leads to ametropia of 3D. For example 1 mm shoening in axial length causes hypermetropia of 3D. 2) Curvature Change in the curvature of cornea or lens will cause ametropia. In hypermetropia, the curvature of cornea or lens is lesser than normal. In myopia, there is increase in curvature of cornea or lens./ mm change in corneal curvature leads to 6-7 D ametropia. 3) Index If refractive index of optical system is low, it will result in hypermetropia and high refractive index will result in myopia. 4) Positional (Due to relative position of the lens), A forward shift of lens causes myopia, backward shift result in hypermetropia. Absence of lens (aphakia) causes hypermetropia. 5) Excessive accommodation Excessive accommodation due to spasm of accommodation causes myopia.
Curvature myopia
Index myopia
Axial myopia
Positional myopia