Make sure your goggles fit properly before swimming! Studies have found that tight, small goggles can actually raise the pressure of your eye to dangerous levels. Did you know that the pressure exerted by certain small racing goggles can raise a person's eye pressure 13 mm? For example, if your normal eye pressure was 15, then when you were wearing the small goggles, your pressure would be 28! The average pressure is between 10-20mm, and if it raised above 21 for prolonged periods of time, optic nerve damage can result and glaucoma can develop. This leads to a gradual loss of peripheral vision and can eventually cause tunnel vision or blindness if not controlled.
The picture above shows several styles of goggles, of which the bottom left goggle is the safest. If in doubt, just bring an extra pair of your goggles in to our office and we can remove the front part and measure your pressure while you wear them in our exam room (see picture E)! Courtesy of Morgan et al, http://bjo.bmj.com/content/92/9/1218.full .
This is not intended to suggest that swimming with goggles can lead to blindness! However, for the serious swimmers, it is in their best interest to use large goggles that do not press too hard on the orbit of the eye. For example, in the above picture, the best goggle style was letter C - it has a continuous interface between the two eyes and the pressure exerted on the orbit was not clinically significant. However, stay away from goggles that look like the one pictured in letter A - that particular style raised eye pressure an average of 5mm. The goggles pictured in letter B and D only raised the pressure by about 1.5mm.
For more information, please read the interesting article published by Morgan et al. at: http://bjo.bmj.com/content/92/9/1218.full. In this study, the measurements had to be taken outside of the water. When under water, the pressure of the water could exert even more force on the orbit, potentially increasing the pressure more. However, there is some good news for swimmers! It is also estimated that 20 minutes of any aerobic exercise like swimming actually decreases eye pressure by about 4 mm.
Therefore, the moral of the story is to keep swimming! However, make sure you are wearing comfortable, nice large goggles. I found a good pair on Amazon.com (pictured below): http://www.amazon.com/Aqua-Sphere-Seal-Swim-Mask/dp/B000EORGXQ/ref=pd_sim_sg_4 .