Hi Ed,
It may take a number of minutes, but your eyes will compensate by opening up the pupils. I don't notice it coming in from outdoors to indoors.
I have Zeiss i.Scription lenses (measured at more points across the eye's lens, which also helps night vision, and modeled more accurately to reduce residual aberrations) in my specs, and I've been told that the plastic lenses go darker than glass lenses and go clearer as well. They are not cheap (an understatement) but have served me well so far. The only negative of my multifocals is that the angle of view is somewhat restricted, when one cannot turn ones head far enough (but that's another issue).
Cheers,
Bart
Hi Bart
Zeiss iScription lenses utilise sightly different technology than is usually employed in manufacturing spectacle lenses. "Ordinary" spectacle lenses correct what are known as low order aberrations (LOAs) (e.g. the short-sightedness/long-sightedness/astigmatism) but about 33% of the population have considerable high-order aberrations (HOAs) too. These are coma/trefoil/sph aberration/etc,etc all within the optical system of the eye, and the Zeiss i-Profier (a wavefront aberrometer)actually measures and quantifies these. Zeiss then have the "knowhow" to combine the information that an optometrist provides to them with the i-Profiler information and manufacture a lens, in single vision or varifocal form, that will correct their vision much more like a fingerprint. Contrast improves as too do colours and vision in poor light, when the pupil is largest and therefore the high-order aberrations most obvious (destructive), becomes much sharper and crisper. Driving at night is one of the most noticeable improvements.
Since I have been using the i-Profier and the resultant i-Scription lenses I have found the results outstanding. Even my own vision is noticeably better and I only just have sufficient HOAs to warrant the i-Scription lenses. I have even been able to prescribe correction for people who I couldn't in the past because they only have HOAs and no LOAs worth speaking of. In 20+ years of practice undoubtedly the best/most useful/most satisfying piece of equipment that I have used.
Zeiss photochromic lenses are made of the same Transitions VI material as many other manufacturers use but the coatings are obviously Zeiss.
You are quite right in stating that glass photochromic lenses aren't as good as plastic and with the exception of Zeiss, glass photochromic lenses tend to be solid. This means that where the lens is thicker the lens is darker and for someone who is quite short-sighted the lens is darkest around the edge and clearer in the centre where it is thinnest. Not cosmetically attractive nor particularly useful. Plastic lenses use a uniform thickness of photochromic material on the surface so the lens tint is always uniform. Here in the UK glass lenses are still used but very, very seldom.
Varifocals all differ in the extent to which you can see peripherally. Partly due to prescriptive restrictions, partly due to the lens design and partly due to the way a frame actually fits your face. You can't "help" what prescription you have, but you do have a choice of lens design. Most manufacturers produce between 3-6 different lens designs, progressively more complicated and expensive. Basically each upgrade in design means slightly more useful area within the lens and less of the distortion zones. Also the distortion becomes less pronounced but even with the best design it cannot be avoided completely.
The fit of a frame can make a huge difference to the overall clarity and visual field that you get through the lens. Manufacturers use certain averages when designing a varifocal e.g. how far it is sitting from your eye, how far apart your eyes are, the angle of the lens in front of your eye and the wraparound effect of the frame. All of these have an effect on the extent to which you can see through a lens and the blurred parts in the bottom corners. Some manufacturers will actually design a lens incorporating these individual measurements and in doing so you end up with glasses with the biggest useful area for your prescription and for the way the frame fits your face. A pair of Zeiss Gradal Individual i-Scription lenses is about as good as I have ever come across, perhaps the Leica Summilux of the spectacle world! (I have no connection with Zeiss and they do not reimburse me in any way for saying all of these nice things - mores the pity!)
Regards
Richard
