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Solutions: Medical Option - the EYE

Q8.

(a) The diagram represents a simplified version of a normal eye, with no sight defects, looking at a distant point object. Complete the paths of the two rays.

    • rays refracted inwards at cornea
    • rays refracted at lens
    • rays focused at the fovea on the optic axis on retina

When a diagram shows you a lens outline the examiner wants you to show that you know light is refraction at it on both entry and exit. If the diagram is too small you can indicate this with a sentence or a mini magnified section inset.

(MAX 2 marks)

(b) Describe the distribution of receptors over the retina.

There are only cones at fovea

As you move away from the fovea, there are more rods and less cones.

(2 marks)

(c)

(i) State the purpose of the iris.

The iris controls the intensity of light reaching retina.

(ii) Describe how this purpose is achieved when the eye is exposed to bright light.

The iris closes its aperture to form a small pupil.

(2 marks)

(d)

(i) State what is meant by accommodation.

Accommodation is the ability of the eye to change the power of its overall refraction system. This allows fine focus of an image on the retina for a range of object distances.

(ii) Describe how accommodation is achieved.

Accommodation is achieved by changing the curvature of the lens
by using the cilary muscles. To focus on a close object the eye lens needs to be more powerful (more curved) than when it views a distant object.

(2 marks)

(Total 8 marks)