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11.7.5 Vision, Disorientation, Illusion

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Spectacles

Don't let this happen to you...

"I picked up my first ever pair of Prescription Sunglasses last week after tiring of the long time summer glare. I had a mild change in my eyes between getting my spectacles and my standard shades, I can understand the difference. I've been wearing glasses for over 10 years now so I'm well accustomed to the changes. However I've NEVER had a pair that threw off my perception of depth like my new Prescription Sunglasses do. Clarity wise, everything is absolutely perfect, however it feels like looking at things through a fishbowl and anything less than ~10ft away becomes incredibly hard to judge distance. It's most noticable when doing simple tasks like judging the distance to the ground, or reaching for the radio in the aircraft."

Today's optometrists play a crucial role in ensuring that these pilots are provided with the proper visual correction they need to function efficiently.

A majority of the pilots who require spectacles for flying will wear single vision spectacles. A thorough eye examination is the first step in properly prescribing aircrew single vision spectacles. A detailed case history should be taken which includes the type of aircraft the aviator flies and the crew position. An accurate refraction is essential for top visual efficiency and the optometrist should be careful not to over-plus or over-minus the patient.

If a pre-presbyopic patient is overcorrected in the minus direction, they may have trouble reading approach plates, especially at night. Over-correction in the plus direction will blur the pilot at far distance with resulting dissatisfaction. Evaluating the final prescription in a trial frame at far distance and at the cockpit working distance is a way to avoid these errors.

A spare pair of clear spectacles is recommended as a backup. Antireflective lenses may be prescribed when reflections due to spectacle lenses create a problem for the pilot. The prescribing doctor should stress to the pilot that a spare pair of clear spectacles should be carried in their flight bag or, even better, their pocket, at all times when flying to serve as a backup in case something happens to the pair they are wearing. This is especially true of pilots who perform aerobatics or who are anticipating flying in turbulence where there is a good possibility the spectacles maybe dislodged.

Sunglasses

Cumulative damage to the retina can occur over a number of years due to glare. Good quality sunglasses give protection by filtering out both blue and ultra violet light.

Sunlight and its Effect on the Eyes

Very high levels of light are encountered at high altitude, especially when an aircraft is flying over a flat sheet of cloud.

Two parts of the light spectrum can cause damage to the eye:

  • Blue Light: Long term exposure may cause cumulative damage to the retina.
  • Ultra Violet (UV) Light: Prolonged exposure to UV wavelengths can also cause damage. UV rays are absorbed by the lens and cause a painful swelling, accompanied by extreme sensitivity to light better known as snowblindness. It is produced only after prolonged exposure to high-intensity sunlight, such as that reflected into the eyes by cloud. Ultraviolet bums do not normally produce permanent damage to the eye. UV wavelengths are normally filtered by the cockpit windshield.