Dr Ian Sibley-Calder has been a GP since 1988, is a medical referee for the UK Sports Diving Committee and is involved with hyperbaric medicine and commercial diving activities. He is a BSAC Advanced Diver and Club Instructor.
I enjoy both scuba and freediving. Instead of an afternoon shallow,
second dive, I sometimes prefer to snorkel, with some freediving (nothing extreme, 15 to 20m at most). However, divemasters have advised against any freediving on the same day as scuba. Is this being overcautious, particularly after a surface interval of more than two hours

This question should really be directed at the technical gurus, but I believe there could well be a problem here. After scuba diving you have tissues in various states of nitrogen-loading. These continue to leak out their nitrogen for many hours afterwards in a gentle way.
Sudden recompression and fast ascents, as with freediving, is potentially going to cause the stored nitrogen to come out in an uncontrolled way, increasing the risk of decompression illness.
That said, I have not heard of this happening to anyone, so would be interested if readers know of anyone who suffered a bend in this way.

On my knee
Within the next few months I may have to have surgery on my knee, either to remove any broken bits of the meniscus or to have the synovial fluid replaced. How long after the operation should I wait before I can start diving

These operations are normally done arthroscopically (keyhole surgery) and involve minimal trauma to the knee. Sometimes complications do occur, such as bleeding or infection, but provided you make an uncomplicated recovery you can dive as soon as any swelling has settled and the knee is pain-free.

Menstruation and breast implants
I wonder if you could help with two questions. Firstly, whenever we go diving and I am menstruating, my husband always tells me (half-teasingly) that the sharks will be able to pick up my scent, and that I am putting him at risk. When diving while menstruating I always use tampons. Are there any contra-indications to diving while menstruating, either due to use of tampons or an increased threat of shark attack
Secondly, I have been considering getting breast implants and wondered if there was any research on the effects on them of increased pressure when scuba diving.

Firstly, there is no evidence that sharks cause any problems to menstruating women. Neither is the use of tampons a problem. As an aside, there has been a little data to suggest that women may be more prone to decompression illness at certain times in their cycle, but this is early data and will need much more study. The increased risks were also very small.
Breast implants are fine as long as they contain no air. Most are either saline-, lipid- or silicone-based, and do not change under pressure. If the enlargement has been significant, then dive equipment may have to be altered accordingly.

Rollerblading head injury
I took my diving medical today, and was failed due to a fit that occurred when I was knocked unconscious 14 months ago. This occurred while I was roller-blading, and hit my head after a fall from height at high speed onto concrete. I was unconscious for a number of minutes, and had a short fit during this time. I was taken to hospital by ambulance and given the all-clear after tests (including a CT, but not an EEG). The doctor failed me because of a worry that I may have epilepsy.

An isolated fit at the time of a head injury with no further problems is unlikely to cause any future problems or increased risk of epilepsy. I am presuming that the head injury was regarded as minor and that there was no significant loss of memory.
I suggest that you are reviewed by a doctor who is interested in diving medicine, and that the guidelines on head injuries published by the UK Sport Diving Medical Committee are studied on www.uksdmc.co.uk

Did diving bring on my migraine
Last summer, two days after a shallow, 70-minute dive at an inland site, I suffered a migraine attack, my first in nearly 25 years (I had a short series when I was about 13). I experienced sporadic visual aura for 30 or 40 minutes and this developed into a bad headache and nausea. Two days later, having felt a little delicate since the first attack, I had a second, with exactly the same symptoms. Is it plausible that diving acted as a trigger to the recurrence of the migraines, and does this condition preclude me from diving

This is a very topical question, in the light of recent research by Dr Peter Wilmshurst, who has published a paper on the association of migraine and right-to-left cardiac shunts (PFOs, or holes in the heart).
Essentially, people with classical migraine (those with aura) are more likely to have a PFO and so more likely to get DCI. Researchers are now looking at getting more information to see if routine closure of the PFO stops the migraines.
So the answer to your first question is yes, there may be an association, and getting your heart tested for a PFO could be worthwhile. Contact a doctor interested in diving medicine and see if he can help arrange one.
Diving with migraine is possible providing the migraines do not suddenly incapacitate you, and you could get out of the water easily.
Medications can be a problem and require expert diving-doctor advice, as they can often cause drowsiness or other problems.

Diving and breast-feeding
My wife is breast-feeding and we are thinking of taking a beach holiday and doing some small dives. Are there any medical reasons why breast-feeding mothers should not dive

The only problems I can see with breast-feeding and diving are size and tenderness of breasts and dehydration reducing milk supply. Divers do have a tendency to get dehydrated due to hydrostatic pressure and with-holding fluids, so extra care would need to be taken to ensure adequate supply, and making sure that your wife drank to her thirst. Locally restrictive equipment could also put pressure on the breast, perhaps leading to an increased risk of mastitis.

hspace=5 I go all misty-eyed
After some dives I have noticed some misting of vision, which clears within a few hours. As a wearer of contact lenses, I first thought that this was caused by drying of the surface of the eye due to breathing dry compressed air. However, having monitored it more recently, it appears to occur on deeper or repetitive dives, which would indicate that something in my eyes is affected by the expansion and slow release of gas on surfacing. Whats causing this, is there anything that can stop it and are long-term consequences likely

The most likely cause is bubbles coming out of solution in your tears on ascent beneath the lenses, causing mild compression of the cornea. These depressions would be mild and would slowly fill in over several hours, restoring the vision. Slower ascents may help, or lenses that are more gas-permeable. There should be no long term consequences.