Astigmatism Reduction: A Common Goal in Refractive and Cataract Surgery

Dr. Noel Alpins

Meeting:  2017 RANZCO


Date:      -

Session Title: Lectures

Session Time:      -

Synopsis: Sir Norman McAlister Gregg gained worldwide attention when he described the link between rubella in pregnant mothers and subsequent cataract formation in their children. Advances in cataract extraction over the course of the 20th century came to include the routine use of intraocular lenses, establishing cataract/IOL as an important refractive surgical procedure through the present day.
Other refractive surgical advances over the past few decades relate to the shape of the cornea. These approaches, ranging from incisional to laser ablative techniques, include the planned correction of astig- matism. The advent of toric IOLs, inserted through a small incision, adds to the complexity of refractive surgical correction of astigmatism.
The measurement of astigmatism and the astigmatic correction induced by these surgical approaches can be based either on corneal or refractive parameters. Historically, surgical planning has been based primarily on corneal values for incisional procedures and refractive values when using the excimer laser. These two con?icting approaches are paradoxical and confusing.
The differences that prevail between the cornea that creates the astigmatism and the refractive cylinder that corrects it optically are prevalent and signiftcant, and can play a role in adverse refractive and qualitative outcomes. Addressing these differences during the planning of the surgery provides a uniform paradigm for all astigmatism procedures. Including corneal in addition to refractive values in the treatment plan reduces the amount of overall astigmatism in the eye and provides advantages in outcomes for any corneal refractive astigmatism surgery.
The inclusion of a corneal parameter became the impetus for an improved corneal measure of astigmatism, called corneal topographic astigmatism, or CorT. This new parameter was developed to give more accuracy than other current measures, such as simulated keratometry (Sim K), when planning refractive surgery.
Several prominent scientiftc journals have adopted these analyses techniques as a standard for reporting astigmatism outcomes in cataract and refractive surgery.