Eye Care Information

<split from post on Crizal anti-reflective coatings>

I have just purchased glasses with progressive Crizal forte UV lenses. I am concerned that they have significant chromatic abberation i.e. colour fringes on high contrast scenes. If I look at a white roof line or trees against a bright sky, I will see a colour fringe, typically blue or at times yellow orange. The effect is more pronounced away from the centre of vision.

I have never experienced this with other coated progressives which I think were a Carl Zeiss product.
Has anyone else noticed the fringing or have an opinion if it is the coating or the lens itself.

I also notice that the reflection of a fluorescent tube shows a strong green reflection where as my old ones have a much fainter blue reflection implying that the Crizal forte UV have a poorer anti reflection performance.

These are the most expensive glasses I have ever purchased and would appreciate any feedback.

Glochief,

I am guessing you are outside the United States, because I don't believe the Forte or Forte UV are sold in the US. Also, your spelling of "color" and "center" is different than what we use here

Some people say they are the same as the Avance, but for non-US markets, but I haven't gotten definitive explanations. Some claim the Forte is more scratch resistant than Avance, but I'm doubtful that is the case, or it would either be sold in the US, or they would upgrade the Avance or some other line to have the same technology.

Anyway - as to your question. I think there may be two different issues you are raising. First is the "chromatic aberration" and the second is the reflective color you get with your lenses/coating.

You don't mention what strength prescription you have, what material the lenses were made from, or what brand the lenses are (Crizal is the anti-reflective coating - not that brand of progressive lens). If I had to guess why you are getting chromatic aberration with these lenses as opposed to your previous ones, I think it is less likely to be due to the anti-reflective coating and more likely to do with the material of the lenses. Polycarbonate or other high index plastics with a lower Abbe value will in theory have more chromatic aberration. Same thing with stronger prescriptions. The best material for chromatic aberration is glass, but this is not practical for eyeglasses for most people due to the risk of serious injury if the lenses were to crack. Glass has an Abbe value of 58.6. Plastic (CR-39) has the best Abbe value of materials commonly used for eyeglasses at 56.8. Many optometrists don't use plastic because it tends to be thicker and may not be as shatter proof as other materials. Also, I suspect eye doctors can make more money off polycarbonate or higher index materials, but I have nothing to substantiate the claim. The Abbe value for polycarbonate is only 30. Trivex is the lighter option than plastic with a better Abbe value than polycarbonate at 43-45.

So - on the one hand you have lens material affecting chromatic aberration because of Abbe value. On the other hand, you have prescription strength affecting chromatic aberration. One way to calculate how much chromatic aberration you have is to divide your prescription strength (6 diopters) by the Abbe value (30) which gives you a dioptic spread of 0.2 diopters. If you increase the Abbe value with CR-39 you get 6 diopters / 56.8 Abbe = .105 or almost half the chromatic aberration.

Most people don't notice, so you may be particularly sensitive to it. As far as I have been able to research, anti-reflective coatings have no affect on chromatic aberration, so I don't think the Crizal Forte is the reason you are having chromatic aberration. I am guessing the new lenses are either a stronger prescription and/or a different material with a lower Abbe value.

The other comment you made was about the color of the residual reflections you see when looking at florescent light (or any other light for that matter). I don't believe the color of the residual reflection makes that much difference, but is more of a personal preference issue. Crizal Avance has a green/yellow residual color. Zeiss Gold has a gold residual color (yellowish). The higher "light transmission" rating a coating has, the less noticeable the residual reflections will be. I think Crizal claims the Crizal Sapphire coating has the highest light transmission and that coating has a bluish / purple hue to it. I think the light transmission numbers are more of a marketing issue as the Crizal Avance is rated at around 99.2% light transmission while Crizal Sapphire is rated at around 99.6%. I highly doubt that most people can tell the difference.

So, bottom line is that you can't judge the quality of your antireflective coating based on the color of the residual reflections. The color is very much personal preference and most people don't even notice it. In theory, the bigger issues would be scratch resistance, durability, and ease of cleaning. In reality, I haven't been able to tell any practical difference between my $5 Zenni optical anti-reflective coating, my super expensive Crizal Avance coating, or my Costco $30 anti-reflective coating. They all have worked fine for me and have had adequate durability.