Bright Sight

Oliver Backhouse, Consultant Eye Surgeon www.cataract.org.uk

Double Vision

Diplopia is another word meaning double vision. It may seem obvious but double vision is seeing 2 of the same object and not blurred vision. Occasionally double vision can come from one eye as the light is split and this is called monocular diplopia. Causes for this include poor fitting spectacles, unevenness of the surface of the eye (Cornea), cataract formation and disturbance of the retina (light sensitive part of the back of the eye). Double vision otherwise comes from the two eyes not being in the correct alignment.

As general rule, if it is coming from the two eyes in an on / off nature then the likely diagnosis if that of a squint which has been ‘hidden’ for many years now showing itself. It may be more obvious when tired or unwell. This may be able to be corrected with new spectacles, eye exercises and prisms attached to the spectacles. Myasthenia Gravis, a condition where there is blockage of the nerve impulse to the eye muscle by the immune system, and can mimic all types of diplopia but more often the on / off type. Your doctor will ask you specific questions regarding this such as the variability of the diplopia and possible associated drooping of the eyelids.

If the double vision is there all the time clues to the cause can be found in a detailed history of possible trauma, other illness such as Thyroid problems, speed on onset and whether the second image is above / below or side-by-side. A frequent cause of this latter type of double vision is an interruption to the blood vessel that supplies a nerve that controls part of the muscle movement of the eye (see separate information sheet on Microvascular Cranial Nerve Palsies). As Double Vision can be part of a more generalised problem it is important that it is correctly identified. Some Ophthalmologists have a special interest in these disorders and have a dedicated Neuro-Ophthalmology clinic. A Neurologist and Orthoptist may also be in this clinic as well to help with the management. Painful double vision requires an immediate visit to your Ophthalmologist.

The treatment of diplopia very much depends on the cause. Blood tests, X-ray, Magnetic Resonance Imaging (MRI) and some other tests can help find out. If the problem does not fully respond to medication, eye exercises, prisms and spectacle change the sometimes squint surgery (operating on the muscles that move the eye) can be considered. Surgery is only undertaken after the eyes have been allowed to recover as much as they can on their own. This can take many months or even longer especially if due to an accident.