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Intraoperative wavefront aberrometer improves refractive outcomes of cataract surgery
A specialist offers pearls for new users of the device.
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Cataract surgery is one of the safest procedures in all of medicine, and with new technology such as femtosecond lasers and multifocal lenses, it may surpass refractive surgery as a vision-enhancing procedure. With the growing prevalence of post-refractive cataract patients and the additional need for precise measurements with multifocal lenses, the use of an intraoperative aberrometer allows the best refractive measurements possible.
With all of my cataract patients, I take thorough measurements before surgery and use the IOLMaster (Carl Zeiss Meditec) to calculate IOL power. However, approximately 35% of the time I end up choosing a different lens after using the ORA System (WaveTec Vision) intraoperative wavefront aberrometer. Initially, intraoperative readings that differ from preop biometry can be alarming. However, following the intraoperative measurements has resulted in better refractive and visual acuity outcomes for my patients.
There is a learning curve with any new device, and that is true with using an intraoperative aberrometer and trusting the measurements it provides. Following are tips on how to get the best use of an intraoperative wavefront aberrometer.
Surgical techniques
My surgical cataract process is fairly standard. I make an incision, complete the capsulorrhexis, emulsify the cataract, and remove the cortex with the irrigation and aspiration device. I then fill the anterior chamber and prepare the eye for biometry measurements. I tend to use balanced salt solution. Some surgeons feel that they get a more consistent pressure with viscoelastic, but either can be used. Once the eye is aphakic, I repressurize it with balanced salt solution, ask the patient to fixate on the reading device, and take the measurements. There are a number of steps that I take to ensure an accurate and consistent reading.
The key to a good intraoperative measurement is consistent pressure within the eye. A baseline pressure reading should usually be between 20 mm Hg and 25 mm Hg. This starts with a good incision. A less optimal incision allows for leakage of fluid, which prevents stable pressure within the eye.
The second element to consistent and precise readings is to make sure that the anterior chamber is homogenous. Either balanced salt solution or viscoelastic can be used to inflate the anterior chamber, but there should not be a mixture of both.
It is important to ensure that the lid speculum is not putting any undue pressure on the globe and creating an inaccurate reading. I find it helpful to position the patient’s head so that there is an equal amount of sclera showing both superiorly and inferiorly before I start the reading.
I irrigate the surface of the cornea so there are no dry spots. The homogenous surface aids in obtaining an accurate reading.
When taking a measurement, there is a small red light that I ask the patient to find before beginning the reading. Once I know they can see the light and are fixating on it, I begin.
Last, I make sure that I have good focus on the z axis before I initiate measurements. This ensures that the readings are captured more rapidly.
After I take the initial readings, I evaluate if it is necessary to take a second or third reading before making a final decision on which lens to implant. At this point I fill the chamber with viscoelastic to insert the IOL. If the measurements demonstrate a fair amount of astigmatism, I will typically make a limbal relaxing incision as soon as the IOL is in. Once the implant has been placed and positioned, I remove the viscoelastic, leaving just the balanced salt solution. With the eye in the pseudophakic state, I will take another reading to see if I need to augment the limbal relaxing incision.
Similarly, if I am using a toric implant, I take readings of the aphakic eye. This tells me spherical power, cylindrical power and the axis. Once the lens is placed, I remove the viscoelastic and take a reading in the pseudophakic state. At that point, I can evaluate whether the implant is positioned correctly or is off by 5° or 10°. If necessary, I can go back in at this stage and gently nudge the implant in the direction suggested and then take another reading. I may do this once or twice, whatever is necessary to get the implant exactly where it needs to be with no rotation.
Using the intraoperative aberrometer to make a final IOL selection and aid in placement has resulted in an improvement in my outcomes. Previously our enhancement rate was approximately 10% of our cataract surgeries. Since incorporating intraoperative biometry measurements, it has decreased to about 5%. The intraoperative aberrometer is useful in the majority of patients, but I find it really shines with toric implants and post-refractive cataract patients. In these situations, I really insist on using ORA to assist me.
Trusting the technology
Initially it is disconcerting to receive intraoperative aberrometer readings that are different from your preoperative measurements, and it is understandable that we trust that with which we have more experience. When I first started using the intraoperative aberrometer, if the readings were very different, I would trust my preoperative measurements. This was particularly true in cases in which the intraoperative measurements recommended a lower diopter implant power than my preop biometry. As patients tend to be more bothered by slight hyperopia than myopia, I am more hesitant to put in a lower diopter implant vs. a higher diopter implant.
If you take an intraoperative reading and it is vastly different from your preoperative measurement, I recommend taking a second reading. If you get two intraoperative readings that are very similar, you will have greater confidence in them. If the second reading is different from the first, check your variables (eg, eye pressure, speculum) and take a third to see what the trend is. Overall, the readings are very consistent and reproducible, and the time to take a reading is between 15 and 20 seconds. Taking multiple readings and ensuring that you have selected the right lens and placed it correctly will have very little impact on your overall surgical time.
Marketing the technique
There is obviously a cost involved with offering this kind of precision to patients, so we created three different options for cataract patients in our practice. The first is the basic package. This procedure includes just the services typically covered by insurance companies and is used with patients who are not really interested in what their refractive outcome will be.
The second package we have labeled a custom cataract procedure, and it is for the patient who wants the best possible monofocal vision. This patient does not mind wearing glasses for near visual acuity, but they want good distance vision. This patient may need a limbal relaxing incision if they have a lower level astigmatism, or they may require a toric lens if they have a higher level of astigmatism. Our custom cataract procedure includes use of a femtosecond laser as well as the intraoperative aberrometer to help guide us with the selection and placement of the IOL.
The top tier package we offer is laser-assisted cataract surgery with the femtosecond laser and the intraoperative aberrometer. This option is distinguished by inclusion of a premium multifocal lens, which provides the patient with excellent vision at all distances.
These packages provide options for all of our cataract patients while allowing us to compensate for the cost of new technology.
An intraoperative GPS
We have an increasing number of patients who come to us because they want a choice, and they are willing to pay additional fees to receive optimal outcomes. I always go into the operating room with two or more IOLs. The IOLMaster gives me a good initial starting point with lens selection, and the ORA System acts as a GPS to guide me to the final choice. With an intraoperative aberrometer I have greater confidence in my ability to provide predictable results for my patients.