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PART B: OPTICS OF INSTRUMENTS EXAM PAPER 2011

1. a) Describe how a bio-microscope may be used with a Hruby lens to view the fundus of a

subject.3 marks

-See lecture notes.

b) If the magnification provided by the bio-microscope is 25X, power of the Hruby lens is 55 D, and

the subject is an unaccommodating standard emmetrope, find the overall magnification obtained by

using the bio-microscope with the Hruby lens. 2 marks

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2. a) A Keratometer gives the power of a cornea as 46D@ 90 and 44D@180.

Assuming a notional index of 1.3375, find the radii of curvature along the principal

meridians. Give a rough sketch of the appearance of the image of the circular mire

pattern seen on the subjects cornea. How much is the corneal astigmatism? Is it

with the rule or against the rule? 3 marks

b) While using a Keratometer, the actual size of the Purkinje-I image is 3.30 mm.

But, it was measured as 3.28 mm. If the actual power the single surface cornea is

43 D what will the measured power be? 2 marks

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3. In spot retinoscopy the sighthole is 66.67 cm in front of the subjects eye. The immediate

source is 100 cm in front of the subjects eye. K= 1.00/-1.0060. The illuminating beam is

driven rightwards (along 0 degree) from the centre of the subjects pupil. No working lens is

used.

i) Calculate the relative reflex speed along the principal meridians. 3 marks

ii) Find the direction of the reflex movement. 2 marks

4. Values of meridional refraction obtained for a subject along 0, 45, and 90 degrees are F0= 1.50 D,

F45= 2.87 D, F90= 2.50 D. Find the Fspof the subject in ve spherocylindrical format.

5 marks

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5. The spectacle correction for both the eyes is 8.00 DS, centred for the DPD of 64 mm. The

working distance is 40 cm in front of the eye. The distance of the centre of rotation of the

eye from the spectacle plane is 30 mm. Calculate the effective prism power C.

5 marks

-See class notes/CE solution.