Ultrasound sulcus-to-sulcus measurement enhances sizing for implantable lens

Current FDA-approved white-to-white measurement incompatible with sulcus-to-sulcus method.

BOSTON — Ultrasound sulcus-to-sulcus measurement is more precise than white-to-white measurement in sizing a posterior chamber phakic IOL, a speaker said here.

“My opinion is that it should become the standard of care,” Paul J. Dougherty, MD, said at the American Society of Cataract and Refractive Surgery meeting. “I do not think you should be putting in a posterior chamber lens unless you have a sulcus-to-sulcus measurement with an ultrasound.”

Dr. Dougherty presented results of a study using the Sonomed ultrasound biomicroscopy device for sulcus-to-sulcus measurement before implantation of the Visian implantable Collamer lens (ICL, STAAR Surgical).

White-to-white measurement is the U.S. Food and Drug Administration-approved method for ICL sizing, Dr. Dougherty said. However, the method has been shown to be incompatible with sulcus-to-sulcus measurement.

“The assumption was that white-to-white would closely follow sulcus-to-sulcus,” he said. “That’s a very poor assumption.”

The FDA study using white-to-white sizing had a 17% rate of poor sizing, with either over- or under-vaulting.

“This can lead to a lot of problems with exchange,” Dr. Dougherty said. “For instance, the biggest risk factor for developing cataract with a posterior chamber lens is a lens exchange. So, you’d really like to try to avoid that.”

Risks of low or excessive vault

Lenses that are too long can result in angle closure, Dr. Dougherty said.

“If the lens is too long, you can run into problems with angle closure, which is a nightmare,” he said.

If the lens is too short, shallow vault increases the risk of the implant touching the crystalline lens, as well as the chance of cataract formation.

Dr. Dougherty cited a previous study comparing ultrasound biomicroscopy sulcus-to-sulcus and white-to-white measurements. Results showed that 100% of the ultrasound biomicroscopy patients had ideal vault of between 200 µm and 800 µm. Conversely, 53% of patients in the white-to-white measurement group had ideal vault.

“Now, why should we use [ultrasound biomicroscopy] for phakic IOL sizing? [It’s] all about getting great outcomes and minimizing risk to the patient,” Dr. Dougherty said. “Clearly, white-to-white leaves something to be desired.”

Ideal vault is about 500 µm, or one corneal thickness. Inadequate vault is less than 90 µm. Excessive vault is more than 1,000 µm, which increases the risk of angle closure, Dr. Dougherty said.

“I find that 200 µm to 800 µm is great,” he said. “Good vault range is 90 µm to 1,000 µm.”

Significant boost in accuracy

The prospective multicenter trial included 61 eyes of 61 patients aged 21 to 45 years with average myopia of about –7.6 D. Sonomed’s VuMax 2 was used to make all sulcus-to-sulcus measurements.

“I’m routinely doing low myopes with ICL as well as high myopes,” Dr. Dougherty said. “Quite frankly, in my practice, my average level of myopia is probably –5 D to –6 D with ICL.”

Results showed weak correlations between angle-to-angle and sulcus-to-sulcus, and white-to-white and sulcus-to-sulcus measurements. No patients had unacceptable vault based on sulcus-to-sulcus measurement. Conversely, white-to-white measurement resulted in a 15% to 20% rate of unacceptable vault.

Average vault was about 344 µm, ranging from 93 µm to 952 µm.

If the FDA sizing method were used, 65% of patients would have required a different lens; 34% of patients would have required a different lens if STAAR’s optimized white-to-white measurement method were used, Dr. Dougherty said. – by Matt Hasson

• Paul J. Dougherty, MD, can be reached at Dougherty Laser Vision, 321 N. Larchmont Blvd., Suite 1020, Los Angeles, CA 90004, U.S.A.; +1-323-466-7337; e-mail: info@doughertylaservision.com; website: www.doughertylaservision.com.