Another SNP was associated with more pronounced furrow contractions, which are circular and radial bands that result from the iris folding in exactly the same location each time it adapts to different light conditions. A third SNP, located near the SLC24A4 gene, was linked to pigmented rings that are visible around the pupil and distinguish different shades of green and hazel eyes. Interestingly, previous studies have also linked SLC24A4 to differences in eye color (blue versus green eyes). Since pigmented rings on blue irises can cause the eye to appear green or hazel, the authors of this study suggest that the presence or absence of pigmented rings may drive the association between and eye color.The authors noted that older participants tended to have more furrow contractions and pigmented spots on the iris. Males had more crypts than females, but fewer pigmented spots on the iris, furrow contractions, or pigmentation rings.It is interesting to wonder why no two irises are the same and this study suggests that some of the differences are due to our genes. These findings also add evidence to the idea that the iris and brain are tightly linked starting very early in human development. Thus, while iris patterns can be used to tell people apart, they may also truly be a window into our minds.SNPwatch gives you the latest news about research linking various traits and conditions to individual genetic variations. These studies are exciting because they offer a glimpse into how genetics may affect our bodies and health; but in most cases, more work is needed before this research can provide information of value to individuals. For that reason it is important to remember that like all information we provide, the studies we describe in SNPwatch are for research and educational purposes only. SNPwatch is not intended to be a substitute for professional medical advice; you should always seek the advice of your physician or other appropriate healthcare professional with any questions you may have regarding diagnosis, cure, treatment or prevention of any disease or other medical condition.