A list of options are given for divers with vision problems. This includes masks with corrective lenses, gas permeable and soft contact lenses as well as disposable contact lenses. Each one is suitable depending on the individual’s needs and problem.
More than half of all Americans require some form of visual correction. Recreational diving transports us into a unique environment in which vision becomes our primary sensory link to the aquatic world around us. Clear, comfortable vision on a dive is as important as careful preparation and selecting the right equipment. Poor vision can decrease our appreciation of the underwater environment and place us in unnecessary danger. In this article, we will explore a number of options available for achieving correct vision underwater. These range from a mask with corrective lenses to traditional rigid, gas permeable and soft contact lenses to the diver’s most recent option, disposable contact lenses.
One of the most common ways of correcting vision while diving is to the use of a specially designed mask. Mildly near-sighted individuals do not usually require correction because a standard dive mask provides 25 to 30 percent magnification underwater. Moderate to high amounts of refractive error are not compensated for by magnification, however, and correction is usually desired.
There is a variety of different mask styles to choose from, depending on individual need. If you are interested in incorporating corrective lenses into an existing mask, lenses can be bonded to the faceplate or a hinge can be inserted on the inside, upper portion of the faceplate to which a spectacle frame can be attached. A third option is to have a special faceplate optically ground to your prescription. In any case it is important to choose a mask with extremely low volume, allowing the faceplate to be as close to your eyes as possible.
In many cases a bifocal lens may be needed. Near vision should not be overlooked – reading gauges is as important as seeing colorful tropical fish. Divers over age 40 who need eyeglasses for reading may benefit from a corrective lens for reading gauges and viewing small objects. It is also a good idea to have your prescription checked by an eyecare professional who understands divers’ special requirements. Important instructions can be included with the prescription to aid the technician at your local dive shop in tailoring your mask in accordance to your needs.
There are many considerations in deciding between contact lens wear and mask correction. A contact lens wearer will not have decreased vision during transit to the dive site or on the boat before entering the water. Mask correction leaves the diver with poor vision until the mask is put on. The same holds true at the completion of the dive; vision is compromised until the diver’s glasses are retrieved.
For many years, it was generally accepted that contact lenses were unsuitable for diving for a variety of reasons. A few of the more common questions regarding contact lenses and diving include: Are the eyes getting enough oxygen? What is the effect of increased pressure and gas bubble formation? Is there a high risk of losing the lenses?
In order for the cornea (the front part of the eye) to be transparent, it must be free of blood vessels. It must therefore receive oxygen from another source; namely the air and the tear film that wets the eye. When a contact lens is placed on the cornea, the amount of oxygen getting through is reduced. The decrease varies, depending on the thickness, diameter and oxygen permeability of the contact lens. As we know, pressure equalization in the mask is achieved with exhaled air. The partial pressure of oxygen in exhaled air is higher and the air more oxygen rich than the air we normally breathe on the surface. Therefore, the cornea actually receives more oxygen through the contact lens while diving then it would on the surface.
Nitrogen and other inert gases, which make up 79 percent of breathing air, are not involved in body metabolism. As we know, the only way these gases dissolve in the body is under pressure. The tear film (the cushion between the cornea and a contact lens) is no exception to this rule and will take up inert gas as partial pressure rises. Good tear film exchange, achieved through normal blinking, will flush away any tiny bubbles that develop. However, when there is a poor tear film exchange, bubbles could be trapped under the contact lens. This usually occurs where the tear film layer is the thinnest. These gas bubbles, trapped between the cornea and contact lens, enlarge during ascent. If the diameter of the bubbles remains smaller than the thickness of the tear film, visual changes are not likely. However, if their size becomes greater than the thickness of the tear film, blurred vision can occur. The bubbles cause tiny dents in the cornea that affect vision. Once on the surface, it can take 15 to 20 minutes for the bubbles to disperse and vision to clear. Removing, rinsing and rewetting the lenses will minimize the duration of blurred vision. Under no condition can these bubbles become large enough to pop the contact lens out of your eye, as was originally believed. A slow ascent, especially in the last 33 feet, when gas expansion is the greatest according to Boyle’s Law, seems to reduce the possibility of blurred vision.
As mentioned, blinking is a very important factor in tear film exchange and washing away these bubbles. In addition to poor tear film exchange, decreased blinking can dry your eyes, making contact lens wear uncomfortable. Concentration and observation while diving is one thing that can lead to decreased blinking. The 100 percent humidity that exists inside a dive mask can also fool your eyes into decreasing the amount of normal blinking. Making sure you blink frequently, thereby rewetting the lenses, can help to avoid difficulties.
Contact lens loss while diving is not as likely as you would think, although it can occur. A rigid gas permeable contact lens, which is smaller and much harder than a soft lens, is seldom lost underwater when properly fitted. Only exposure to strong turbulence can cause this type of lens to pop out. Soft lenses fit the eye differently and can be lost more easily. If you become separated from your mask either above or below the surface, a good rule of thumb is never open your eyes completely. This will allow the edges of your upper and lower lids to overlap the edges of your contact lenses, preventing them from popping out. Clearing a flooded mask is easily accomplished by keeping your eyes closed until most of the water is gone.
The introduction of disposable soft contact lenses has made losing a lens less of a concern. As disposable lenses are intended to be discarded after use, a lost lens is no longer a tragedy. Disposable contact lenses are good choices for people who normally wear glasses or for those who do not want to risk losing the contact lenses they wear regularly. Disposable lenses can be dispensed in multi-packs of six and used exclusively for diving. At the completion of a dive the lenses can be thrown away. Extra lenses can be kept in your gear bag.
In closing, it is important to mention that all points considered apply mainly to diving at recreational depths. Most of the literature maintains that the mechanism of gas bubble formation and the role decompression plays are not completely understood. Also, there are certain criteria for successful contact lens wear and not everyone is a good candidate. For example, a person with very dry eyes may have difficulties and would probably be better served with a mask correction. An eye exam would best determine which type of vision correction for diving best suits the individual. Seek an eyecare professional with diving experience and an understanding of the diver’s special visual needs. As with all aspects of the sport, careful preparation is the key to safe, enjoyable diving.