Right as you're boarding the helicopter for your flight, your pilot happily announces she just had surgery on both eyes to remove cataracts. Would you turn around and get right back off? Probably so. Vision is a pilot's most vital tool, and no mechanical equipment can replace it. A serious impairment to her vision can lead to mistakes, miscalculations and misreading the panel instruments, all of which can have fatal consequences. So, yes, healthy vision is a top priority for pilots of all types of aircraft. That being said, not having perfect, 20/20 vision is not an automatic disqualification.
Perfect, or Perfectly Correctable
In an ideal world, pilots would have 20/20 vision in each eye. Being that this world is less than ideal, pilots whose distant vision can be corrected to 20/20 through glasses or contact lens are eligible, as are those whose near vision is correctable to 20/40 at 16 inches. Pilot candidates who are over the age of 50 must have 20/40 in each eye at both 16 and 32 inches. If you must wear corrective lenses in order to have 20/20 vision, then it's a condition of your license that you always wear them while flying.
There's one exception to the 20/20 rule: pilots cannot wear bifocal contact lenses, says the Federal Aviation Administration. Contacts that are specially designed to provide perfect distance vision in one eye and perfect near-sighted vision in the other require the wearer to constantly shift her focus from one eye to the other as needed. Suppressing vision in one eye in favor of the other impacts both depth perception and the ability to coordinate eyesight from both eyes.
A pilot may actually qualify for her license even if she only has one functional eye. This is called monocular vision. It must have been at least six months since the accident or condition that caused the monocular vision, and she must undergo a complete eye examination. Her vision must be at least 20/200 and correctable to 20/20; however, the prescription in the lens can't be any stronger than plus or minus 3.5. The fact that candidates with monocular vision are eligible while candidates who need bifocals aren't may seem like a contradiction. The difference, though, is that people with bifocals never have the opportunity to adapt to vision out of just one eye, as they're always alternating between eyes.
Factors Affecting Sight
There are more factors than just poor vision that can affect your eyesight. Before taking the vision test for aviation, make sure you've had plenty of rest the night before. Avoid consuming alcohol or smoking cigarettes, as both can blur your vision. Taking medications that make you dizzy or sleepy can also impact your vision, as can self-imposed conditions like hypoglycemia, which can be avoided by eating properly.
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