Purpose and methods: The incidence of forward bowing of the iris, width of the iridocorneal angle, and distance between the apex of the angle and the scleral spur were studied using high-frequency (50 MHz) ultrasound B-scan images in 90 normal eyes from Japanese volunteers.
Results: The incidence of forward bowing of the iris, defined as a 120-micron anterior shifting of the posterior profile of the iris, increased from 0% in subjects under 31 years old to 50% in subjects 71 years of age and older. The iridocorneal angle was significantly narrower and the distance between the apex of the angle and the scleral spur was significantly less in eyes with forward bowing. Of the risk factors (age, axial length, sex, and corneal curvature), age (p = 0.0005) was the most significant risk factor for forward bowing of the iris.
Conclusion: Forward bowing of the iris is not uncommon in the elderly. Half of the Japanese subjects in this study 71 years of age and older had this condition, even though they had no optic nerve atrophy or elevation in intraocular pressure (IOP) at the time of examination.