Fig. 2. The Tono-Pen hand-held tonometer (A) and Bio-Pen biometric ruler (B) are ideally suited to the examination of young children in the operating room or office. Young children who have become accustomed to having pressure measurements taken with the Tono-Pen usually accept the Bio-Pen as well, permitting A-scan biometry to become a routine part of follow-up examinations in the office.