Seeing is believing. Make sure your underwater vision is all that it can be! Photo: David Fleetham.com
By Dr. David Sawatzky
In the last three columns I reviewed vision underwater, common refractive errors, and reading glasses/ contacts. In this column I will finish the discussion of vision and diving by looking at various mask options for correcting your vision while under water.
Do You Need to Correct Your Vision?
Diving with a mask results in everything appearing to be 25 per cent larger and closer than it really is. If you wear glasses that provide relatively small amounts of correction, your vision while diving with a normal dive mask is often fine. As a rough rule of thumb if you can legally drive a car without glasses, you will not need to correct your vision to dive. The one common exception to this guideline is someone who needs reading glasses. They do not need to wear them while driving, but they will usually not be able to read their gauges while diving without some form of correction.
Some divers wear their glasses under the mask. If the arms on the glasses are very thin and flexible, this might work. In general however the mask will leak. Other divers take the arms off an old pair of glasses and mount the front part of the glasses inside the mask. The mask will not leak and the visual correction will be OK but it is hard to keep the glasses in position, it will be hard to clean them, hard to avoid fogging, and just plain ugly! Fortunately, there are several much better options.
Bonded Lenses
One of the first reasonable options available historically (and still available today) was to have special lenses ground that provided the same correction as your glasses but with perfectly flat fronts so that they could be glued onto the inside of the glass in your dive mask. They can be put into any mask with a flat faceplate (common), one or two front windows, but not into a mask with a curved faceplate (rare). These lenses will provide excellent visual correction because they can be ground for any prescription including astigmatism, bifocals and even prism. I dived with this kind of mask from 1982 until 1996 (when I had laser eye surgery) and it worked very well but there are some limitations and drawbacks.
The lens is smaller than the glass in the mask so you will not have correction for your peripheral vision. This is also true when you wear glasses so it is only a minor problem.
It is difficult to clean the faceplate of the mask around the lens so it will tend to get quite dirty (not the end of the world).
If your correction is large (more than five diopters) and normal glass is used, the lens will be very thick and you will get a ‘coke bottle’ effect. Special ‘hi-index’ glass can be used to reduce this consequence, the same as in glasses.
The mask skirt will eventually wear out but it can usually be replaced. Sometimes the lenses can be removed from your old mask and inserted into a new mask, but by then enough time has usually passed that you really need a new prescription anyway.
The lenses have to be positioned correctly in the mask or they will not work properly. We all have different sized heads and our eyes are different distances apart. The lenses have to be correctly lined up with the eyes to work well.
If you decide to pursue this option, buy a dive mask and dive with it several times to ensure that it fits well, does not leak and that you are happy with the mask. Then take the mask to a place that knows how to do this process. The distance between your pupils will have to be measured and you will need to know the prescription for your glasses. Some dive shops and some optical stores provide this service. Typically you will have to send the mask away to have the lenses mounted in the mask. This may take a couple of weeks and can be fairly expensive.
In spite of these limitations this is a reasonable way to correct your vision while diving, and your vision will be nearly as good as it is with your glasses.
Prescription Masks
If you buy a mask with a split face plate, it is sometimes possible to replace the glass on each side with a lens that has been ground to the same prescription as your glasses. This is a better option than bonded lenses but tends to cost a bit more. In addition, you cannot usually move the prescription lenses to a new mask but have to have new lenses ground. This option is normally arranged through your dive store and is an excellent way to correct your vision while diving.
Drop-in Lenses
A simpler and less expensive option is to buy a mask that has been designed to use ‘off the shelf’ corrective lenses. These corrective lenses are usually available in half-diopter increments and cover the most common visual requirements. You buy the mask, the dive store replaces the glass in the mask with the prescription lenses that most closely match the spherical equivalent of your glasses prescription and you are ready to go. There are also several masks that you can order with these ‘off the shelf’ lenses already installed.
This option works extremely well as long as you do not need significant astigmatic correction, bifocals, prism, etc. Your visual correction is not perfect, but it is usually so close that the difference does not matter. A quick search on-line turned up over 300 different dive masks for which you can now order corrective lenses, both prescription and drop-in!
Reading Glasses
Bonded lenses and prescription masks provide the same correction as your glasses, while drop in lenses historically only corrected for distance vision. If your distance vision is okay and you only need reading glasses, there are a few options.
Special reading lenses can be purchased that you glue into your mask near the bottom so that you can look through them to read your gauges. Flexible reading lenses that adhere to the inside of the mask with water surface tension are also available but I was pretty unimpressed when I tried them. Any water in your mask at all and they tend to move or come off.
Another option is to buy a mask that has small windows at the bottom into which you can put reading lenses. These masks work well but tend to be fairly large and only fit if you have a fairly wide face.
You can also get bonded lenses or a prescription mask with a bifocal correction where the top is only glass. However, you can now also order masks or replacement windows for your mask with the reading correction ground into the bottom part of the lens. The correction is available in half-diopter increments. This seems to be the best option at the moment and should not be that expensive.
“HydroOptix” Dive Masks
I would not normally discuss a specific product, but this one is so unique that it deserves mention (check out www.hydrooptix.com). The HydroOptix dive mask has curved lenses. The curved lenses allow for a much larger field of view (they claim 5 times that of a flat mask) and the resulting image is sharper (they claim 100 times sharper). The curved mask windows convert the water into a corrective lens!
To try and simplify a very complex topic, these dive masks will give superior vision compared to a normal flat mask, but the vast majority of divers will have to wear corrective contact lenses to make the mask work for them. The only exception to this requirement is that of divers who need correction for near sightedness within a specific range and who do not need bifocals, astigmatic correction or prism. Divers who require -2.5 to -6 diopters of correction under age 30, -3.5 to -6 diopters around age 35 and -4 to -6 diopters over age 40 can use the mask as is and just wear their glasses on the surface.
All other divers (including those who do not need glasses) will need to insert special contact lenses just before each dive and take them out immediately after the dive, or wear special glasses to see on the surface while wearing the contacts. The masks are not that expensive but when you add the special contacts and glasses it adds up. I personally don’t think the increase in vision is worth the added expense and “hassle factor” but for a professional underwater photographer it probably is. Either way, this is a highly innovative product.