National and international standards help to ensure the safety, reliability, and quality of products and services. Although adherence to consensus-based standards is completely voluntary, it promotes a fair commercial environment and greater confidence in the products we use, particularly when they are precise medical devices.
For nearly a century, the American National Standards Institute (ANSI) has sought to enhance the global competitiveness of US businesses by promoting the development of standards. Contrary to popular belief, ANSI is not a governmental body but rather a nonprofit organization consisting of companies, institutions, governmental agencies, and other members. It is the United States' representative to the International Organization for Standardization, which fulfills a similar role globally.
ANSI does not develop standards itself but rather accredits Standards Developing Organizations (SDOs) to ensure openness, balance, consensus, and due process. The ANSIaccredited SDOs, in turn, conduct the laborious process of creating individual American National Standards. Of more than 200 ANSI-accredited SDOs, the one with greatest relevance to ophthalmology is the Z80 committee, which establishes standards for glasses, contact lenses, IOLs, viscoelastics, corneal lasers, and many other ophthalmic products. Eighteen organizations are represented on this committee, including the American Academy of Ophthalmology, the American Society of Cataract and Refractive Surgery, the American Optometric Association, and the FDA.
TORIC IOL STANDARDS
The current American National Standard for toric IOLs, approved in March 2010, is known as ANSI Z80.30-2010. It provides guidance on optical and mechanical properties, labeling, biocompatibility, sterility, shelf life, and clinical investigation standards for toric IOLs.
Two important guidelines specified by the ANSI standard are (1) recommended tolerances for the spherical and cylindrical power and (2) rotational orientation and stability. Without tight power tolerances, accurate refractive outcomes would be impossible. Because a rotational error of just 5º results in a 17% loss of cylindrical power, rotational orientation and stability are critical as well.
For toric IOLs, total dioptric spherical power and cylindrical power error should be less than or equal to 0.30 to 0.50 D for most power ranges. Additionally, the combined angular error of the toric marks and the orthogonality between meridians of toricity should be 5º or less.
The ANSI standard also defines the rotational stability for toric IOLs to be a change of 5º or less in rotation for at least 90% of eyes on consecutive visits spaced at least 3 months apart. Stability should be reported for both a consistent cohort (eyes with every follow-up examination) and a consecutive cohort (eyes with two consecutive examinations).
This is an important and high standard to meet, as surgeons who implant toric lenses know. Of the current toric IOLs on the market, toric plate lenses (STAAR Surgical) have had some challenges in terms of stability.1 Acrysof Toric lenses (Alcon Laboratories, Inc.) are generally considered stable, but because they were released prior to the ANSI Z80.30-2010 standard, their labeling data do not follow the ANSI reporting standard. Rotation of 5º or less was reached for only 77% to 88% of eyes, but the data were reported for longer intervals of nonconsecutive visits.2 According to its labeling, only the Tecnis Toric (Abbott Medical Optics Inc.) currently meets ANSI standards for rotational stability, with 94% of eyes experiencing a rotation of 5% or less between the 3- and 6-month visits.3
CONCLUSION
The ANSI standard for toric IOLs was developed through a process of openness, balance, consensus, and due process. It functions as an important guideline for the evaluation of toric IOLs' safety and effectiveness.
Daniel H. Chang, MD, is in private practice at Empire Eye and Laser Center in Bakersfield, California. He is a consultant to Abbott Medical Optics Inc. Dr. Chang may be reached at (661) 325-3937; dchang@empireeyeandlaser.com.
- Chang DF. Comparative rotational stability of single-piece open-loop acrylic and plate-haptic silicone toric intraocular lenses. J Cataract Refract Surg. 2008;34:1842-1847.
- Acrysof Toric IOL [package insert]. Fort Worth, TX: Alcon Laboratories, Inc.; 2009.
- Tecnis Toric IOL [package insert]. Santa Ana, CA: Abbott Medical Optics Inc.; 2013.
