Consider the accommodated crystalline lens of the eye as an isolated unit having

Question

Consider the accommodated crystalline lens of the eye as an isolated unit having radii of curvature and effective refractive index as given for the schematic eye 2' (4^th column in the table in chapter 8). a Using the definition of the refractive power P = Delta n/R, calculate the refracting power of the accommodated lens (schematic eye 2') in its actual environment. b) Calculate the refractive power and focal point of the equivalent lens of the whole schematic eye 2' (notice that the thickness of schematic eye 2' doesn't change relative to schematic eye 1)

Explanation / Answer

(a) consider eye as a optic medium with only one surface of refraction. If the aye is surrounded by air

1/a+(n'-1)/r=n'//b'

Refractive power realtive to air P=n'//f'=(n'-1)/r

Using concept of vergence write Snells law for refraction V+P=V'

If the surrouding medium is not air P=n'//f'=(n'-n)/r

example: n=1.33 and n'=1.34 for average eye, radius of curvature of cornea r=0.0057 m . Then P =1.75 diaptor

(b) Under water this gives a focal distance of about 76 cm inside eye.

You can use this formula for any values of n and n' and r to find Power (P) and focal length (f)

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