'A' Level Medical Option Questions - The EYE
Q13.
(a) State the changes which occur in a normal eye when:
(i) the eye changes from focussing on a distant object to focussing on a near object, both
objects being viewed in bright light
Ciliary muscles contract or suspensory ligaments relax 
Producing a lens of greater power orshorter focal length
(2 marks)
(ii) the eye changes from viewing an object in very dim light to viewing the same object in
bright light.
(Iris circular muscles contract and /or radial muscles relax produces) constricted pupil or the pupil becomes smaller
Cones turn on and the signal from them is so much stronger that the rods become effectively inactive
(2 marks)
(b) State two differences in the perceived image of a coloured object viewed in bright
white light compared to the perceived image of the same object viewed in very dim
white light.
Colours are seen in bright light, but the image is only in monochrome (black and white) in very dim light
Good detail in bright light, but much less detail in very dim light
(2 marks)
(c)
(i) A patient’s eye is astigmatic. State the effect of astigmatism on the image produced
by the defective eye.
Image is focussed in a given plane and out of focus in
the plane perpendicular to it
(1 mark)
(ii) State the usual cause of astigmatism.
non-spherical cornea
(1 mark)
(iii) State the shape of lens used to correct astigmatism.
cylindrical lens
(1 mark)
(9 marks Total)
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