MRI of the orbits: what it is, safety checks and what to expect

The orbits are the bony sockets that hold the eyeballs. Besides the eye itself they contain the optic nerve, the muscles that move the eye, fat, blood vessels and the lacrimal (tear) gland. An MRI of the orbits is a scan focused on this region, usually with the area around the brain and the nerve pathways imaged as needed.

NHS inform describes MRI as a type of scan that uses strong magnetic fields and radio waves to produce detailed images of the inside of the body, and says it can be used to examine any part of the body. The scanner is a large tube that contains powerful magnets, and the scan is painless.

The NHS says MRI scans can be used to find out what is causing any symptoms, check bones and organs and see how well a treatment is working. For the orbits, doctors may use it when they need soft-tissue detail that is not obvious from an eye examination alone, for example when investigating sudden or unexplained changes in vision, pain on eye movement, double vision, a bulging or displaced eye, swelling around the eye, or when assessing the optic nerve.

It is also one of the tests that can be used when thyroid eye disease is suspected or being monitored. The British Thyroid Foundation describes thyroid eye disease as an autoimmune inflammatory disorder that affects the orbit, mainly seen in people with an overactive thyroid caused by Graves' disease, and says that early diagnosis is essential. In the UK these patients are cared for jointly by an eye specialist and a thyroid specialist.

Which scan is used depends on the question being asked. Your eye specialist, neurologist or endocrinologist will explain why an orbital MRI, a brain MRI or another type of scan has been chosen.

Before any MRI you will be asked to fill in a form. The NHS lists questions about whether you are pregnant or may be pregnant, are breastfeeding, have had surgery, have kidney problems, have metal parts in your body such as surgical clips, a pacemaker, dental fillings or bridges, or have allergies including to contrast dye. You may be asked to remove metal items such as jewellery, hearing aids and hair clips and to change into a gown.

Because strong magnets can move metal fragments, an orbital scan raises a specific safety question. NHS Greater Glasgow and Clyde MRI physics guidance, written for staff, describes asking whether you have had an eye injury, whether you were examined at the time and told that any foreign body was removed completely. If the injury involved a metallic object and you were told it was not fully removed, or you think metal may have entered your eye but you never had an eye examination, the MRI is postponed and you are referred for screening radiography. Only if that shows no foreign body can you go ahead.

In practical terms, tell the radiology team if you have ever had an eye injury involving metal, for instance from grinding, welding or drilling, even if it was many years ago. Local policies vary, so the hospital doing your scan will give you specific instructions.

An MRI is done in hospital by a radiographer. The NHS says that you lie flat on a bed that moves into the scanner, are given ear plugs or headphones because the scanner makes loud bangs and clicks, and need to lie still so that clear images can be taken. For a scan of the orbits the radiographer will tell you how to keep your head and eyes still during the pictures.

If you are anxious or have a fear of small spaces, the NHS advises talking to a healthcare professional before the appointment, and says you may be able to have a medicine to help you relax. You can ask whether someone can come with you. If you are given a sedative, you will need someone to take you home and should not drive for 24 hours.

Contrast medium, if used, is given by injection. The NHS says side effects are usually mild, such as feeling sick, a rash, a headache, a metallic taste or dizziness, and that allergic reactions are rare. You may be asked to wait around 30 minutes afterwards.

The images are looked at by a radiologist, who writes to the doctor who referred you. The NHS says this usually takes 1 to 2 weeks, and that if you have not heard anything after a few weeks you should contact the referring doctor.

The report is only one part of the picture. Your doctor will combine it with your symptoms, eye examination and other tests, and will explain what happens next. If you do not understand a report, ask for it to be explained.

In the NHS, an MRI of the orbits is requested by a hospital doctor, eye specialist or sometimes a GP, depending on local rules. Private scanning is available in many cities, usually with a referral from a doctor, and uses the same safety screening. Whichever route you use, make sure the team knows about any metal in your body or previous eye injuries.