By Michael Hutton 

Contact lenses for swimming  which are only worn while sleeping and are specially designed to enable water sports participants to see clearly without requiring prescription goggles also provide the perfect solution for those who enjoy the extreme sport of freediving. And by not having to wear normal daytime contact lenses this ensures the risk of serious bacterial infection from water-bound microbes can be avoided. The prevalence of these bacteria carriers in both open water and in indoor pools - even in showers and baths - is not widely recognised by daytime contact lens wearers yet some 75 people develop an infection every year in the UK which can lead to loss of sight as the microbes literally eat their way into the eye having initially been trapped between the contact lens and the surface of the eye.

Freediving is an aquatic technique which has a number of competitive variants all involving extended breath-holding and the current no-limits female world record holder is Briton Tanya Streeter who reached a depth of 525 feet in March 2002. At that point this was a world best for men and women and justified her earlier induction in 2000 into the Women Divers Hall of Fame. But freediving is not just a sport. For people like the Bajau of South-East Asia who live in stilt houses at the edge of the sea, freediving is a way of life and they can fish underwater for up to five minutes on one breath. However, studies have shown that this naturally achieved attribute can be matched by people who take up freediving later in life which is where the special contact lenses for swimming  become a key factor.

Successful freedivers make use of the mammalian dive reflex which is a series of automatic adjustments made when submerged in cold water, reducing the heart rate and metabolism to slow the rate of oxygen consumption. Whilst holding breath for an extended period, oxygen stores reduce and the body starts diverting blood from hands and feet to the vital organs. This is compensated by the effect of the underwater pressure constricting the spleen thus squeezing out extra haemoglobin, the protein in red corpuscles that carry oxygen around the body. However, like scuba divers, freedivers have to manage the issue of decompression carefully as they return to the surface to avoid ‘the bends' and hence great eyesight provided by the special contact lenses for swimming  is a key aid to monitor depth changes as they ascend.

See if you are suitable for orthok corrective contact lenses .