Cyclotorsional registration improves wavefront outcomes

August 15, 2004

San Diego-Cyclotorsional registration is an important step to optimize wavefront-guided ablations, according to refractive expert Marguerite B. McDonald, MD, who spoke during the American Society of Cataract and Refractive Surgery annual meeting.

San Diego-Cyclotorsional registration is an important step to optimize wavefront-guided ablations, according to refractive expert Marguerite B. McDonald, MD, who spoke during the American Society of Cataract and Refractive Surgery annual meeting.

The refractive surgeon needs to align the preoperative diagnostic information and laser information to avoid inducing cyclotorsional errors, explained Dr. McDonald, clinical professor, department of ophthalmology, Tulane University, and director, Southern Vision Institute, New Orleans.

Dr. McDonald showed how different degrees of cyclotorsional rotation affected visual function, with residual point spread function (PSF) and the blurred eye chart letters. With 5° of cyclotorsional rotation, the patient experiences significant blurring. By 15° and 30°, the letter E on the eye chart is unrecognizable, she said.

Two methodsThere are two ways to compensate for cyclotorsional registration: manually marking on the sclera with head adjustment and automatic iris image registration.

With the manual method, the surgeon uses an ink mark applied to the sclera at the 3 and 9 o'clock positions or the 6 and 12 o'clock positions at the slit lamp, she explained.

The patient's head is manually manipulated at the laser to match up the ink marks to the laser reticle.

"The disadvantages are that human error is possible," she continued. "The ink marks are time sensitive and very small rotations are difficult to assess."

The automated method using iris image registration is recommended because it automatically aligns the preoperative diagnostic and laser iris images and is not prone to human error, Dr. McDonald said.

Other advantages include the ability to measure small rotational movements, identify the patient and the eye prior to ablation, and allow the surgeon to "re-register" intraoperatively for noticeable cyclotorsion.