Exercise 10 Consider the un-accommodated crystalline lens of the eye as an isola
ID: 1437593 • Letter: E
Question
Exercise 10
Consider the un-accommodated crystalline lens of the eye as an isolated unit having radii of curvature and effective refractive index as given for the schematic eye in the table 19-2 on the slides of chapter 8.
a) Calculate its focal length and refracting power as a this lens in air
b) Calculate its focal length and refracting power in its actual environment, surrounded on both sides with fluid of effective index 1.33. Assume a thin lens.
c) Calculate using the matrix techniques its focal length and refracting power by treating it as a thick lens of thickness 3.6 mm.
Explanation / Answer
(a)
the focal length (f) is given by
(1 / f) = (n - 1) [(1 / R1) + (1 / R2)])
where n is the refractive iondex, R1 and R2 are radii of curvatures
(1 / f) = (1.45 - 1) [(1 / 10) + (1 / 6)])
(1 / f) = 0.1197
f = 8.35 mm
(2)
if it is surrounded with water of refractive index 1.33 then the refractive index of glass with trspect to water is
ngw = 1.09
(1 / f) = (1.09 - 1) [(1 / 10) + (1 / 6)])
f = 4.166 mm
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