Tono-Pen® – reliable pressure measuring pen. The Tono-Pen XL Applanation Tonometer is a portable and easy-to-use instrument that provides IOP readings that are closely related to the Goldman manometry. Tono-Pen XL ergonomic, lightweight design and advanced electronic measuring technology allow operators to perform fast and accurate IOP measurement with minimal training. Weighing in at just 2.1 ounces, the Tono-Pen XL is extremely easy to carry making it easy to take IOP measurements anywhere for any patient. Designed and assembled in the USA.