Intraoperative aberrometer evolves with new standard for accuracy

Take-home message: New, highly accurate aberrometer technology is now available for the intraoperative confirmation of spherical, toric, and multifocal IOL power.

By Warren Hill, MD, Special to Ophthalmology Times

Mesa, AZ‒Refractive outcomes are now the benchmark by which ophthalmic surgeons are judged by both patients and peers. Thanks to ever-improving methods of biometry, along with advanced formulas such as Holladay 2, Olsen, and Barrett, pre-operative surgical planning has improved dramatically, but outcomes are not always consistent. And patient expectations have never been higher.

New technology

HOLOS IntraOp represents the most recent evolution in the technology of intraoperative aberrometry. If Shack-Hartman is like a painting and Talbot-Morié is like a snapshot, at 90 measurements per second, the new, single detector sequential aberrometer from Clarity Medical Systems is more like live, streaming video. With a displayed range of -20.00 D to +20.00 D, a dynamic range from -5.00 D to +16.00 D, and an accuracy of ±0.13 D at the corneal plane, this next generation technology is poised to set a new standard for IOL power confirmation at the time of surgery.

The HOLOS IntraOp aberrometer is based on the principal of a rapidly rotating micro electro-mechanical system (MEMS) mirror that projects a wavefront from the eye through an aperture. The scanned wavefront is focused onto a quad detector that translates the magnitude of the wavefront displacement of a scanned spot into real time refractive data. All of this takes place at incredible speed.

Who benefits?

Experience with the use of intraoperative aberrometry in its current form for normal eyes undergoing cataract surgery shows that the individual surgeon typically moves up to the next tier in terms of refractive outcomes at a ±0.50 D accuracy level; most commonly from the high 70% to the mid-to-high 80% range, with some even higher.

Of course, all patients benefit from improved accuracy, but those who would benefit the most are those who desire a decreased dependence on spectacles. This includes patients receiving standard monofocal, multifocal, and toric IOLs.

For the toric IOL, we now understand the importance of the posterior cornea. But with current technology, a consistently accurate determination of the magnitude and the direction of the posterior corneal power remains elusive.

With an ability to measure differences in refractive power in different meridians, intraoperative aberrometry is uniquely suited for use with the toric IOL. This is because aberrometry is able to arrive at a net solution of the combined power of the anterior cornea, the posterior cornea, and the toricity of the IOL within the capsular bag.

Other clinical situations where intraoperative aberrometry may help lessen the likelihood of a refractive surprise would be unusual eyes where standard IOL power calculations may give less predictable results, such as corneal dystrophies with unusual anterior and posterior corneal power distributions, extreme axial hyperopia where the effective lens position takes on added importance, eyes with unusual anterior segments that fall outside the normal operating areas of even the most advanced theoretical formulas, irregular astigmatism and prior refractive surgery in the form of myopic or hyperopic PRK or LASIK.

For the use of multifocal IOLs, this technology adds a level of confidence that the target spherical equivalent will be achieved.

In the OR

In the operating room, HOLOS IntraOP displays continuous, real-time refractive data. Sphere, cylinder, and axis of cylinder are presented without perceptible delay and require no interaction or adjustments by the surgeon or the operating room staff. There also is instantaneous refractive feedback regarding other influences, such as pressure on the globe by the lid speculum, variations in IOP, and the condition of the ocular surface. No adjustments are required of the room lights, or the illumination of the microscope.

Following IOL implantation, a pseudophakic wavefront is acquired, processed, and automatically displayed. These real-time data then are used for the conformation of the spherical power of the IOL, or optimal toric IOL rotation and cylinder power determination. This also can be used for titrating the reduction of refractive astigmatism by LRIs.

For the unusual case, where the implanted IOL power might result in a large refractive surprise, the IOL power error can be identified and an exchange performed before the patient leaves the operating room.

Planned advances

For 2015, HOLOS IntraOp will be available for pseudophakic IOL power confirmation: standard IOLs, multifocal IOLs and toric IOLs. In 2016, HOLOS IntraOp will add the ability to calculate accurately an IOL power based an aphakic measurement.

Warren E. Hill MD, FACS

E: hill@doctor-hill.com

Dr. Hill is the Medical Director of East Valley Ophthalmology in Mesa AZ. He is a consultant to Clarity Medical Systems, one of several original beta testers of the HOLOS IntraOp aberrometer.