What pilots should know about prescription eyewear:
Clarity and durability are extremely important. Materials such as glass offer excellent optical clarity but are heavy and will shatter on impact. Cheaper materials such as CR-39 are not impact resistant and can’t be used as safety glasses. There are only two materials in regular use for prescription lenses that offer impact resistance – Polycarbonate and Trivex. Of the two, Trivex offers much better optical clarity. It is a trademarked and patented material made by PPG. If you have a strong prescription the best solution may be High Index materials which offer thinner lenses.
In order to obtain the most accurate prescription lenses, you should speak to your optician about getting two additional measurements in addition to your standard prescription. The reason for this is that the most modern and high technology lens manufacturing devices can create your lens prescription throughout the entire lens. This is especially important if you’re getting prescription lenses in compound curve sunglasses. But they can only do this if they know exactly where your eyes are when your glasses are positioned on your face in their normal place.
The two additional measurements are:
With regards to multi-focal lenses such as bifocals and Progressives, you have a choice on exactly where the fitting height is placed on the lens. If you typically use the Reader portion of the lenses to view, say, an instrument panel that is directly in front of you, then you should let your optician know to set the fitting height as high up the lens as practical. This will allow you to view the instrument panel easier without having to tilt your entire head upwards to look through the Reader portion. For some people, this is distracting and not needed, so in their case they would ask their optician to lower the fitting height measurement a bit.
Typical lens tint colors are either gray or brown/copper. Both of these colors can work just fine in the cockpit. It’s really just a personal preference. Also, know that lens tints have no effect on UV protection. Even lenses that are perfectly clear can offer perfect UV protection. In addition to visibly clear UV coatings (look for UV400), lens materials such as Polycarbonate offer natural UV protection on their own.
Gradient tints are an excellent solution for most pilots. This is where the lens is darker towards the top and slightly lighter towards the bottom of the lens. This often makes it easier to read the instrument panel while still blocking harsh sunlight coming through the windshield. The gradient can be quite subtle so that only the wearer really knows that they’ve got gradient tint lenses.
& HARD COATING
Depending on the lens laboratory that you use, this can be an option or a standard feature. It’s very important to ask for scratch resistance as it can greatly extend the life of your lenses. But no matter how strong the scratch resistance you have on your lenses, you should still treat them with care.
CARE OF YOUR LENS
We recommend that you keep your prescription glasses in a protective case that’s designed for your frames when you’re not using them. And only clean the lenses with a micro-fiber cleaning cloth with either water or an approved lens cleaning fluid.
The best Ultraviolet eye protection rating is UV400 which means that it blocks at least 99.9% of UV rays.
Contrary to popular belief, polarized lenses offer no more UV protection than non-polarized lenses. All they do is block a specific angle of visible light. This is very useful for blocking visible glare off of water or snow on the ground. However, because LCD displays on instrument panels and computer tablets such as iPads use polarization in their screens, adding polarization to your eyewear can mean that the screens will visibly dim or even go completely black. It’s for this reason that the FAA advises against wearing polarized lenses.
LENS SHAPE AND CURVE
Depending on your prescription and the type of lenses and frames you prefer, there will be limits to what many lens manufacturing laboratories can offer. For example, sport sunglass frames with a strong wrap or curve to them will usually be limited to prescription strengths of +/- 3.50. And there are some labs that cannot manage any prescriptions with frames and lenses that have a strong curve. However, the best labs will have the technology to handle lenses with strong curves and can create lenses that enable you to see very clearly throughout the entire lens.
BIFOCALS AND PROGRESSIVES
People over 40 will probably have heard of the term Presbyopia, which is a natural occurrence where your near vision becomes blurred.
It often means that you will need dual focusing areas on your prescription lenses, for which there are several options:
These are lenses which darken when outdoors in the sunlight and lighten in the shade or at night. The best photochromic go completely clear at night. Unfortunately, most photochromic don’t work in the cockpit because they use natural, unfiltered UV light to darken the lenses. Cockpit windshields of acrylic or glass will naturally block a great deal of UV light. The only brand and model of photochromic lenses that do work in the cockpit are Transitions XTRActive brand. They will darken when it’s sunny out even when you’re in the cockpit and go completely clear at night.
Other common coatings available are anti-glare coatings which can be both front and back-side of the lens. If your frames and lenses are relatively flat and have the ability to reflect light on the back side of the lenses from light around the back side, then you should ask for anti-glare coatings on both sides of your lenses.
Three other popular coatings are anti-fog, hydrophobic, and oleophobic coatings. Anti-fog coatings are useful for working in cold or humid environments while hydrophobic is very helpful for wet environments such as what seaplane pilots deal with when docking. And oleophobic coatings can help keep your lenses free of greasy fingerprints.