While a multifocal intraocular lens (IOL) implant can cause various visual issues, it should not cause a severe loss of visual field to one side. You need to see an ophthalmologist for a complete evaluation, to include a visual field exam and a dilated retinal exam.
thank you for your comment I have had a field of vision test which seems to confirm that there is a problem. I have contacted Bristol eye hospital to try to arrange diagnostic testing