Vision Correction
A common method for correcting underwater vision is to incorporate a correcting lens into a dive mask. Since a standard dive mask provides 25-30% magnification due to the refraction across the water to air boundary, mildly nearsighted individuals do not usually require optical correction underwater. Moderate to high amounts of refractive error are not compensated for by magnification and corrective lenses are usually needed.
Lenses can be bonded to the face plate of your mask or a bracket can be inserted on the upper portion of the face plate to attach a spectacle frame. Another option is to have a face plate optically ground to your prescription. If you use lenses in the mask, choose a low volume mask to bring the face plate close to your eyes.
Near vision should not be overlooked. Reading gauges or a decompression computer is as important as viewing colorful fish. Divers over age 40 who need eyeglasses for reading, may benefit from a corrective lens for reading gauges and viewing small objects.
Contact Lenses
There are many considerations in deciding between contact lenses and spectacle mask correction. A contact lens wearer will have normal vision during diving and when out of the water. Mask correction requires the diver with poor vision to carry a pair of glasses on the dive to see properly when not in the water.
For many years, it was thought that contact lenses were unsuitable for diving. There were concerns for the eyes getting adequate oxygen, bubble formation under the lens, and the risk of losing a lens. In order for the cornea (the front part of the eye) to be transparent, it must be free of blood vessels. It receives oxygen from the air and the tear film that covers the eye. When a contact lens is placed on the cornea, the amount of oxygen getting to the cornea is reduced. The decrease varies depending on the type of contact lens. Since the air in the mask will have a higher oxygen partial pressure while diving, the cornea receives more oxygen through the contact lens while diving then it would under normal conditions on the surface.
The tear film which is present between the contact lens and the cornea will take up nitrogen and other inert gases as partial pressure rises. Gas bubbles can form between the cornea and contact lens and will enlarge during ascent. These bubbles trapped between the contact lens and the cornea may cause blurred vision. After a dive, the bubbles may require 15 to 20 minutes to disperse and the blurred vision to clear. Removing, and rewetting the lenses will minimize the duration of blurred vision. Blinking is an important factor in washing away these bubbles. Pay careful attention to make sure you blink frequently, thereby rewetting the lenses to avoid difficulties.
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 to prevent the lenses from popping out, is to open your eyes only partially. Clearing a flooded mask is easily accomplished by keeping your eyes closed until most of the water has been cleared.
Soft, disposable contact lenses are intended to be discarded after use, so a lost lens is not a concern. Disposable lenses dispensed in a pack containing several lenses can be used just for diving. Extra lenses can be kept in your dive bag in case a lens is lost during a dive.
Frequent Questions
Is it safe to dive after receiving an artificial lens? These are inserted surgically inside the eye to replace a damaged natural lens. Once the eye has healed, it is possible to return to diving. A waiting time of 3-4 months is usually recommended.
Can I dive with Glaucoma? This is a disease which causes increased pressure inside the eye. If untreated, it will lead to blindness. The increased pressure is always relative to ambient pressure, so diving does not increase the effective pressure in the eye. If Glaucoma is treated and pressure inside the eye is normal, it is safe to dive.
Can I dive after cataract surgery? This surgery is done to remove a cloudy lens. It is a common procedure, and restores vision in many people who otherwise would be unable to see clearly. An artificial lens is usually inserted in place of the cloudy lens. Once the surgery is healed (3-4 months), diving can be done safely.
If you have concerns about your eyes, you should have an eye examination, including a check of your vision and measurement of the pressure inside the eye. Proper advice about corrective lenses, and identification of problems inside the eyes are important parts of maintaining good health.
