Prescription Mask vs. Contact Lenses

[Rick Murchison]

Let's take a look a the optical properties of the mask lens/water interface and what that means to your vision. In your OW class you learned that things look "25% closer and 33% bigger" under water - to translate that to what we see on the surface, the optical distance from up close to infinity under water is equivalent to only eight feet or so in air. And things that are close to you, like your gauges and your watch are optically even closer.
When looking at your topside vision, what this all means is that if you have normal vision (20/20) and normal accomodation, or you're a little nearsighted (you can focus fine in air from about eight feet away and closer), you don't need any correction to see well under water. Water has a natural correction for nearsightedness built in, but makes farsightedness worse. My experience is that if you have reasonably good accomodation (a reasonably good range over which you can focus) then a single correction lens that's skewed about a diopter toward positive will look pretty good under water (e.g. if you are nearsighted and your corrective lens is -2.5 diopters, you'll like -1.5 in your mask). Most farsighted folks, especially "older" folks whose farsightedness is mainly due to a loss of accomodation (lens is less flexible) find that they'll need bifocals - perhaps just the addition of some little magnifiers in the bottom of the lens to read their gauges (and to see the little guys - some of the world's most interesting critters are the little guys) - but if your farsightedness is extreme enough that you can't focus inside eight feet you'll need the help of full-blown prescription lenses or contacts to see anything at all clearly under water. If your accomodation is tight enough that you need trifocals to see well, you'll probably be happiest with the Mares ESA mask, which has a set of lower lenses built in where you can put your near-vision prescription and leave the front lenses for distant and mid-range.
Disclaimer - the foregoing are from my observations of real world experiences and I ain't your eye doc.
Rick

 

[devjr]

Good comments Rick. Older divers who use contacts to correct nearsightedness may find that resulting distance vision is good but near objects, like gauges, are fuzzy. This is due to presbyopia which is the accomodation problem you referred to. There are bifocal contacts available but I'm not sure how effective they are while diving. Some of them seem to depend on gravity for orientation.

Some divers who used the old hard contacts, which apparently are still available for astigmatism, experienced problems with "fogging". This occurred when the diver surfaced, and was not relieved by removal of the lens. The cornea itself was fogged, and it usually took about a half hour for things to return to normal. This would resolve whether the contact was removed or not.

Also, it seems that this fogging problem has occurred if the eye/contact was merely exposed to fresh water, swimming, taking a shower, etc.

I heard some opinions to the above. Examples were "bubbles" and water absorption. Regardless, I don't know of any permanent impairment from this phenomenon. I haven't heard of anything similar with soft contacts but maybe someone has something to add to this.

 

[Drew Sailbum]

I got tired of the hassle of the contact lenses, so switched to a prescription mask.

I normally wear glasses, but got contacts after losing my glasses to the lake gods - 5 times (really!) - while sailing. I got tired of messing with the lenses while diving, so I save that for windsurfing now.

 

[carlislere]

I use contacts when I dive. I do have a prescription mask as a backup in case I were to lose a contact, which has happened on one occasion in 1800+ dives. I also use the prescription mask to demo AI and Divemaster pool skills.