Grading system holds promise for improved efficiency, safety

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The high-resolution Scheimpflug images obtained with a cataract surgery femtosecond laser were used to grade lens density and determine surgical technique.

By Cheryl Guttman Krader; Reviewed by Harvey Uy, MD

Quezon City, Philippines-High-resolution Scheimpflug imaging (HRSi) technology incorporated in a proprietary cataract surgery femtosecond laser system (LensAR) provides unique information on lens anatomy that can help surgeons tailor their approach to achieve optimal results.

“Evaluation of lens anatomy with HRSi can allow surgeons to choose the appropriate nuclear disassembly technique and phaco machine settings, and it requires no extra effort because the imaging is built into the process of the femtosecond laser-assisted cataract surgery,” said Harvey Uy, MD, consultant at St. Luke’s Medical Center, Quezon City; Pacific Eye and Laser Institute, Makati City; and clinical associate professor of ophthalmology, University of the Philippines.

“In the future, I envision a new world of cataract surgery in which the femtosecond laser imaging software will automatically export Scheimpflug image measurements to the phaco machine that will then automatically call up the appropriate parameters for the surgery. Just as MRI guidance has revolutionized neurosurgery, I foresee the Scheimpflug images will revolutionize cataract surgery into an image-guided procedure,” he said.

Dr. Uy presented the results of a study in which 52 eyes underwent HRSi-guided femtosecond laser-assisted cataract surgery using the LensAR system. All cataracts were graded preoperatively by a certified LOCS III grader assessing slit-lamp images. Intraoperatively cataract grading was performed based on the lens appearance in the Scheimpflug images. Using the images, the eyes were categorized into three groups, and surgical technique was based on the categorization. Eyes with a soft/moderate cataract underwent a prechop technique (40%), those with a dense cataract and adequate cortical space to use a chopper underwent counter prechop (50%), and eyes with a dense cataract with inadequate space had stop and chop (10%).

“In eyes where there is no cortical space visible on the Scheimpflug image, the second instrument used for a prechop technique may inadvertently cause capsular damage, and so a stop and chop technique is considered safer,” Dr. Uy said.

All of the eyes had a successful outcome after undergoing the HRSi-guided femtosecond laser-assisted cataract surgery. The only complication was a small posterior capsular tear that occurred with a postocclusion surge. However, it was still possible to place the IOL in the bag and the patient had a good visual outcome, Dr. Uy noted.

Correlation analyses

In addition to the grading of the cataracts from the slit-lamp images using the LOCS III system, a grader masked to those scores categorized the density of the cataracts based on the Scheimpflug images using a scale of 1 (very soft) to 6 (very dense). There was a high positive correlation between the HRSi-based cataract grading and the preoperative LOCS III nuclear opalescence scores. However, an analysis of the relationship between cataract grade and utilized ultrasound energy, represented by the Cumulative Dissipated Energy value on the phacoemulsification machine (Infiniti Vision System, Alcon Laboratories), showed a stronger correlation with the Scheimpflug image cataract rating than with the preoperative LOCS III grading.

Because of this strong correlation, the surgeon can adjust ultrasound, vacuum and flow settings to suit the HRSi-measured nuclear grading, Dr. Uy said.

“For example, for a soft cataract, the ultrasound power can be minimal with low vacuum and flow essentially to aspirate the nucleus,” he said “For a very dense cataract, higher phaco power, vacuum, and bottle height may be utilized together with more extensive chopping maneuvers to minimize utilized ultrasonic energy.

“Also, a femtosecond laser feedback loop can be created where the imaging software selects the optimal laser treatment algorithm for lens fragmentation,” Dr. Uy added. “In the future, the imaging, lens fragmentation and phaco machine software will be merged together to create seamless, customized treatment algorithms for femtosecond laser-guided cataract surgery.”

Power of high-resolution images

Dr. Uy presented Scheimpflug images showing eyes where a prechop procedure could and could not be used based on visibility of the cortical space. In addition, he showed the Scheimpflug image from an eye with a moderately dense nuclear cataract and a posterior polar cataract that was not identified on the slit-lamp image.

“Detection of the posterior polar cataract allowed us to achieve successful surgery by adjusting our technique, including lowering the machine settings and avoiding hydrodissection,” he said.

Harvey Uy, MD

E: harveyuy@yahoo.com

Dr. Uy is a consultant to LensAR and Alcon Surgical. This article is adapted from Dr. Uy’s presentation during Refractive Surgery 2012 at the annual meeting of the American Academy of Ophthalmology.