MEDICAL FAQs

QUESTION

ANSWER

To tell you the truth, I have never come across this in a diver before. As always, an anatomy lesson for starters. In those human beings lucky enough to possess one, the brain sits happily in the skull, linked to the spinal cord which traverses the whole length of the vertebral column (backbone). The aperture in the skull through which the spinal cord passes is called the foramen magnum (Latin for “ice cream” “big hole”). At this junction there is a chunk of brain called the cerebellum, which deals with co-ordination of various senses and motor control. It’s this portion we’re testing when we do all those “standing on one leg with your eyes shut” manoeuvres in dive medicals. Arnold and Chiari were both German pathologists, who independently noted cases where a part of the cerebellum had protruded (“herniates”) through the foramen magnum, sometimes with other abnormalities such as spina bifida. This herniation can block the flow of blood and the cerebrospinal fluid that bathes and protects the spinal cord, resulting in a variety of symptoms – dizziness, odd eye movements (such as your nystagmus), muscle weakness, numbness, headache, and problems with co-ordination and balance. Basically a checklist of DCI symptoms. There are several types of Arnold Chiari malformation, with type 1 luckily the most benign.

Despite extensive searching I couldn’t find a similar case in the diving literature, so I can only offer my own musings on the potential issues here. Firstly there is the perennial problem of diagnostic confusion, as the symptoms of the malformation can be so similar to those of DCI. Secondly, and more seriously, if you were to suffer a case of cerebral decompression illness then it is possible that some herniation of the lower parts of the brain could occur through the malformation, which could be fatal. How likely this is is anyone’s guess, but it’s the severity of this consequence that leads me to the conclusion that it is probably too risky for you to dive safely. I would have no problem with you snorkelling, but without any other evidence it’s the only safe recommendation I can make.

QUESTION

ANSWER

Secondary anophthalmia (the technical term for what you’ve got, or in terms of eyes, not got) is pretty rare, and its cause is unknown, although it appears both hereditary and environmental factors are involved. There’s very little that can be done to treat it, other than try to preserve the vision in the good eye as far as possible. Implants can be used for cosmetic reasons but before puberty these need to be changed regularly to keep pace with the enlarging eye socket. For diving purposes, the HSE guidance advises that “visual acuity with or without correction and colour vision must be adequate for the type of diving activity such as the requirement to read a watch, computer, depth gauge, tables, instrumentation etc.” Practically speaking, you’ll have monocular vision, so depth perception will be diminished, but other than this there should be no problem with achieving these requirements to an adequate degree. Hence I can’t think of a legitimate reason that you should not pass the HSE on these grounds.

QUESTION

ANSWER

There are lots of potential causes of visual blurring after diving. Many are to do with contact lenses – gas bubbles underneath them, dryness, they’ve scooted up under the eyelids or been otherwise misplaced etc. So if your boyfriend is a lens wearer then try some lube first. Other possibilities include corneal scratches, sunburn of the eye, irritation from anti-fogging mask solutions, or anti-seasickness medication side effects. Rarely one sees visual blurring in decompression sickness, but usually with other symptoms as well. However, high partial pressures of oxygen can indeed affect vision, as you allude to in your query. One of the commoner side effects of treating patients with hyperbaric oxygen is a temporary deformation of the lens, that causes a degree of short-sightedness. This is of the order of 0.25 dioptres per week and is progressive, but usually reverses when treatment is stopped. Most cases return to normal within 6 weeks but it can take up to 12 months. It’s extremely unusual in recreational diving, but has been reported. I would expect the same return of vision once exposure to hyperoxic gas mixtures ceases, so I doubt he will cause permanent damage to his eyes, but nevertheless would suggest he stops this type of diving until he is back to normal. With very long hyperbaric oxygen inhalation, visual blurring can progress to field constriction, loss of vision and hallucinations, and eyelid twitching often heralds a full-blown seizure. Luckily removal of the oxygen will stop the fit, but if this occurs underwater, you can imagine the consequences are potentially fatal.