American Board of Ophthalmology (ABO) Practice Exam

The multiple anti-reflective layers of an AR lens stack are primarily designed to do what?

1. Reduce glare for night vision

2. Enhance color contrast

3. Cause destructive interference to different light colors

4. Increase durability of the lens

The correct answer is: Cause destructive interference to different light colors

The multiple anti-reflective (AR) layers of an AR lens stack are primarily designed to cause destructive interference of different light colors. When light hits a lens surface, some of it is reflected while some is transmitted. By utilizing multiple layers with specific refractive indices and thicknesses, these coatings are engineered to create conditions for destructive interference. This means that the reflected light waves from each layer can cancel each other out at certain wavelengths, significantly reducing the overall reflection and maximizing the transmission of light through the lens. This principle enhances visual clarity and comfort, particularly in environments with bright light or glare, since less light is reflected off the lens surface. This leads to a clearer and more comfortable viewing experience. Consequently, lenses with AR coatings improve contrast and can provide a crisper view without the distraction of reflections, enhancing the overall performance of the eyewear. The other responses focus on different beneficial effects of AR lenses but do not capture the fundamental purpose of the multiple layers as accurately as the correct answer. While AR coatings can help reduce glare and enhance contrast, the mechanism of using destructive interference is the core function driving these benefits.