Virtually anyone who has spent time in a swimming pool has at one time or another opened their eyes while under the water. Perhaps you forgot to bring your goggles along and need to retrieve a dropped item. No doubt you experienced blurry vision at those times, and perhaps mild irritation and redness later in the day. This prompts a larger question - are there long term, harmful effects caused by opening your eyes underwater in a swimming pool.
First, let's discuss why your eyes get irritated and red. The water chemistry in a swimming pool needs to be closely monitored so that the water stays free of algae and other living organisms. Most pool operators use chlorine to accomplish this. However, contrary to what you may have heard, the chlorine in the water is not the cause of eye irritation. The actual cause is the water's pH level. This is a measure of how acidic the water is, and it must be within a certain range for the pool chemicals to be effective. If the pH is above or below this range, then your eyes get irritated whenever water is in them.
So, on to the question of long term effects. Unless the water's pH or other chemicals are extremely out of balance, your eyes won't experience any long term harm if you open them under water. There are other dangers and things to be aware of though. If the water has high levels of infectious bacteria, then you could experience an infection in your eyes if you open them under water or they get splashed. If you are swimming at a public pool or in a pool with many young children, it may be wise to use goggles instead. If you wear contact lenses, you will also want to be be aware that you might lose a lens if you are splashed or open your eyes under water. Finally, since your vision is very poor without goggles, you should be cautious about running in to things if you are swimming at a fast pace. Goggles should definitely be worn while swimming laps, because you could injure yourself by running in to the wall at the end of the pool.
To summarize, it's unlikely that opening your eyes in any normal swimming pool will cause any long term problems. However, there are a few items to be aware of. Above all, practice good pool safety and have fun!
