 Photographs of both irises of the healthy volunteers were taken using a digital camera 5-megapixel camera, 1.75 μm pixels, 0.5× digital zoom, LED flash in the same room in daylight, at the same time of day with the same flash. Patients with non-specific and interrupted collarette peripupillar ring limits were not included in the study. An image software program was used to draw circular limits over the iris exterior circle IEC, coloretta circle CC, and pupil circle PC on digital photographs. The areas between the circles were measured. IEC-PC refers to the estimated total area of the dilator plus constrictor muscles stimulated sympathetically and parasympathetically; CC-PC refers to the estimated area stimulated parasympathetically; and IEC-PC-CC-PC refers to the estimated area stimulated sympathetically. The likelihood that the IRIS ratio was equal to the LFHF ratio was calculated using the formula IEC-PC CC-PC CC-PC. The average of three measurements was calculated for each photograph. 