What is a "high index" lens?

Question

I am very nearsighted and my lenses are very thick. I was just at my eye doctor for an exam last week and the optician was telling me that I should have high index plastic lenses, rather than the polycarbonate that i usually get. These lenses she was telling me about are quite a bit more expensive than what I normally get, so I was wondering what these other lenses are, that she was telling me about, and why are they better than the polycarbonate that I usually get, and would it be worth it for me to spend the extra money on them.

Thank you!!

I am -8.50 in my right eye and -8.00 in my left. I wear contacts but not often because my eyes are very dry.

Answer 1

The optical power of a lens depends on the curves on its surface, and its "refractive index". Its optical effectiveness, if you like.
A higher index lens only needs proportionaly flatter curves to deliver a particular optical power, so the lenses can be thinner. The higher the index number, the thinner.

My lenses are slightly less than half as thick at the edge than they would have been if made in conventional plastic.
CR39 1.498
Optical glass 1.523
Polycarbonate 1.54
High index plastics...1.67 to 1.74
High index glass lenses 1.7 to 1.9

( I wear 1.9 index glass in my driving glasses, 1.8 glass in my varifocals as they are not made in 1.9 as yet.
My Rx gets up to -14.00 in the strongest meridian))

There are reasons why all glasses are not the higher index versions.
Apart from cost, the higher index version ones can be more brittle, more easily marked on the surface, heavier, and in many cases the chromatic aberration is worse, leading to coloured fringes and poorer acuity when looking through the periphery of the lenses (not straight ahead through well-fitted spectacles). The exact properties will depend on the material selected. A good antiscratch/anti-reflection coating is almost essential and is usually a standard feature.
Some are not suitable for rimless mounting, which is rarely a good idea with strong Rx's anyway.

High index lenses are worth considering once the prescription gets above about -4.00, depending on the size of the frame. By -6.00 the improvement with high index lenses can be very marked.

But a simple and important factor needs to be added in. With a strong Rx, the frame with the smallest roundest lens shape *that looks good on you* will produce the best looking overall pair of glasses.
Don't go any bigger or squarer than you need to.

Answer 2

In simple terms, a high index lens is a type of lens that refracts light more than a regular lens. Therefore, if the light is refracted (i.e., bent) more in this type of material the lens can be made much thinner. The higher the index of refraction, the tinner the lens.

Pros of high index lenses: thinner, lighter, cosmetically nicer, wider frame selection...

Not sure what your Rx is but in my opinion it's definitely worth investing in high index lenses especially if you wear your glasses all the time.

The optician should actually show you the difference b/w the H.I. lenses and regular lenses. Some brands, like Nikon, provide illustrations to the opticians/optometrists to show to customers...You can take the frame that you selected (marked with your pupil distance) and align it with the illustration to see the final lens thickness on the edges. It's quite informative.

Answer 3

There are 4 distinctive alterations of the Canon 50mm lens, the 50mm f/one million.2, 50mm f/one million.4, 50mm f/one million.8, and 50mm f/2.5 The 50mm f/one million.8 comes closest to the Nikkor 50mm f/2 in terms of specifications. different differences incorporate that the Nikkor lens is instruction manual-concentration basically, that is older and made fullyyt of steel, no longer attainable new anymore, and that is made for Nikon cameras.