“Paresis” means weaker whilst “plegia” means paralysis, where voluntary movement is not possible at all – this means that in those contexts ophthalmoplegia is a worsening of the ophthalmoparesis disorder.
But what are they?
They are both eye disorders in which the muscles controlling the movements of the eye cease to function adequately.
A feature of the disorders which makes life extremely difficult for those who suffer from them is that the eyes are not able to move together – this causes sufferers to see double and is disconcerting for relatives, friends and colleagues.
Another unfortunate feature of the disorders is that they are often accompanied by related underlying neurological disorders in the body such as numbness, weakness of the limbs and general lack of co-ordination.
Symptoms usually begin to appear in childhood, sometimes in adolescence:
• Initially eye muscles begin to weaken
• Drooping eyelids typical of the eye disorder ptosis may begin early before any concept of the disorders
• Difficulties at moving the eyes, followed later by an inability to do so
• Eye pain and associated headaches
• Loss of peripheral vision
What are ophthalmoparesis and ophthalmoplegia caused by?
They can be caused by variety of neurological conditions, restrictions within the orbit (the eye socket) or thiamine deficiency in certain people:
• Neurological conditions
Disorders in the cranial nerves or an increase in intracranial pressure
The cerebral cortex can be damaged similar to the way a stroke acts
• The orbit of the eye
A physical prevention of necessary movement within the eye socket can happen, as in Graves’ disease.
• Thiamine deficiency
A lack of vitamin B1 – thiamine – doesn’t always lead to the development of ophthalmoparesis or ophthalmoplegia, it only occurs in rare instances in people who are susceptible.
Vitamin B1 is found in yeast, nuts, meat and cereals and is often prescribed specifically for people with inflammation of nerves located outside the brain, and some think it may help in warding off Alzheimer’s disease.
The two disorders ophthalmoparesis and ophthalmoplegia may develop into one of several related disorders:
• Ophthalmoplegia plus
• Progressive external ophthalmoplegia (PEO)
• Internuclear ophthalmoplegia
There is little that can be done by way of treatment apart from addressing the physical nature of the disorders – drooping eyelids can be surgically lifted and an eye patch can eliminate the effect of double vision.
There is however a danger in eyelid surgery that the cornea becomes more exposed and subject to drying out, with all the complications that is entailed.
Treatment in the case of thiamine deficiency is straightforward – a course of vitamin B1 tablets is precribed. The vitamin can also be administered by injection.
And in the future?
Mitochondrial DNA is thought to be involved which is leading to research into gene and hereditary factors.