When we as ophthalmologists take cataracts out, we like to replace the cataract with an intraocular lens implant. Some of the newer intraocular lens implants (IOLs) are designed to try to help the patient see at different distances, e.g. at far away distances and up close (reading) as well.
Many of the lens implants that try to do that are called “diffractive” IOLs, which are most often identified by the multiple “rings” visible in the lens itself. Though it is certainly not well established yet, many ophthalmologists are noticing that these diffractive IOLs do not work as well as they might when the patient does not have a nice clear looking vitreous. The vitreous is the “jelly” that fills up most of the eyeball, so light that gets detected in the eye has to pass through the IOL and the vitreous. If the vitreous is full of “junk,” the vision is worse, which is an effect that seems to be noticed much more by patients who have diffractive IOLs.