A patient has a cataract and a cornea that is too curved. Treatment takes place in two stages.
| Stage | Observation |
|---|---|
| Before treatment | Distant letters are blurred and bright lamps have halos |
| After the cloudy lens is replaced | Distant letters are blurred and the halos are absent |
| After the cornea is flattened | Distant letters are clear and the halos are absent |
Which explanation is supported by these observations?
Replacing the cloudy lens moves the distant focus onto the retina; flattening the cornea then stops light scattering and removes the halos.
Replacing the cloudy lens reduces refraction; flattening the cornea then increases refraction and moves the distant focus onto the retina.
Replacing the cloudy lens stops light scattering; flattening the cornea then reduces refraction and moves the distant focus onto the retina.
Replacing the cloudy lens repairs the retinal receptors; flattening the cornea then widens the pupil so distant letters become clear.
102 exam-style questions on Edexcel GCSE Biology 2.4 The eye, covering 2.4.1 Structure and function of the eye and 2.4.2 Eye defects and their correction. Each one has a worked solution and a mark scheme showing where the marks go.