It's a hardware artifact, so no there is nothing you can do except take it to an Apple Store or Apple Authorised Service Provider and see what they say. Try and press for them to cover the cost of replacing the display.
If you live in the EU, you may be able to get it repaired free of charge under local consumer law
, but this depends how long ago you bought it and what country you live in (some EU member states only provide the minimum level of statutory protection required under EU law, which is two years). If you purchased your iMac from Apple directly, you'll need to contact either Apple Support (in the case of Apple Online Store purchases) or the local Apple Store from which you purchased your iMac if you want to go down that route. You'll just need to tell them you want to make a consumer law claim for the problem you've got with the display.