Six months earlier he had been diagnosed with cataract by his previous doctor because of blurred and reduced vision in the right eye, and had apparently been treated with eye drops, but it was getting worse, so he first visited our clinic.
As shown below, the cataract was about grade 1.5 in nuclear hardness, but there was dense posterior subcapsular opacity in the right eye only; since it was unilateral we also suspected trauma, but he said that although he had been in a traffic accident, he had not suffered a blow to the eye.
His left eye, which would not be operated on, had mild hyperopia of +0.5 D and good uncorrected distance vision of 1.5, so when surgery was first planned we offered a monofocal lens set for distance or LENTIS Comfort as candidates for the right eye. He was still in his early 50s and the left eye retained some accommodation, so since he was having surgery anyway, LENTIS Comfort, likely to give at least slightly better near vision than the left eye, seemed to offer more advantages; but at his own wish, as he valued reliable vision, surgery with a monofocal lens was planned.
However, preoperative blood tests revealed considerably high blood sugar, so unfortunately surgery was postponed and rescheduled after blood sugar control. In other words, although unilateral, it may well have been a diabetic posterior subcapsular cataract.
Diabetes treatment then went smoothly, and the surgery took place more than six months after his first visit; but as a surgeon I still felt reluctant to operate on the right eye with a monofocal lens that leaves zero accommodation, so one week before surgery we newly proposed TECNIS Eyhance, which had become available thanks to the postponement. It combines reliable distance vision with a small near add of +0.5 D, and photic phenomena such as halos and glare are equivalent to a monofocal lens, so it matched his wishes, and he agreed to surgery with it. For various reasons certain powers of TECNIS Eyhance have remained in short supply, but thanks to the manufacturer's efforts the lens was made ready just in time for the day of surgery.
The right eye's target refraction was set at mild myopia of about −0.25 to −0.50 so as not to create anisometropia with the slightly hyperopic left eye. Specifically, it is derived from calculations like those below; his cornea was somewhat flat for his axial length of 24.39 mm, with low corneal power of 41.77 D, so standard formulas were predicted to possibly end up hyperopic (our clinic's correction formula predicted a 0.23 D hyperopic error with SRK/T), and we decided to make the final power decision by intraoperative wavefront aberrometry (ORA™ system).
This time I will describe in a little more detail the method and problems of lens power selection by intraoperative wavefront aberrometry with the ORA™ system.
First, the method. Wavefront aberrometry is performed after the cataract has been removed, just before the intraocular lens is inserted; to keep measurement conditions constant, a special lens is placed on the cornea, and intraoperative eye pressure is measured and adjusted to 21 mmHg. Next, the lights are turned off and the patient looks at a small red dot in the center of the wavefront aberrometer attached to the surgical microscope while it measures, 40 times at once to reduce error. The ORA system checks the measured total ocular aberration, together with the axial length and corneal power measured before surgery, against a global database in real time over the internet and displays the predicted refraction for each lens power; at our clinic, to be safe, we measure twice and choose the lens power from the results. This can sometimes add two to three minutes to the surgery, but we believe an accurate result with little refractive error matters far more than a short operating time.
Below is a video of "intraoperative wavefront aberrometry and intraocular lens power selection with the ORA system" (in Japanese).
For him, as described above, based on our clinic's experience-based prediction that the result would end up slightly hyperopic, we used a 21.5 D lens with a predicted refraction of −0.49 rather than the 21.0 D recommended by the ORA system. After surgery, as expected, he had slight myopia of about −0.375 D, and as a result he was very satisfied with uncorrected vision of 1.2 distance / 0.9 near: distance as good as the unoperated left eye, and near even better.
Thus the ORA system is very useful as a tool for reducing postoperative refractive error, but unfortunately at present it is not yet accurate enough to choose lens powers by trusting its results blindly, and it seems safer to use it as simply one more reference value for lens power selection. From our experience using it, I see the following two problems.
(1) In the optimization process, lenses used in large numbers worldwide inevitably have smaller errors, and the fewer a lens is used, the larger its error (for lenses whose lens constant has not been globally optimized, refractive error is larger than with existing formulas).
(2) Anterior chamber depth and lens thickness are not used as parameters.
Regarding (1), because the ORA system is made by ALCON, there is currently a tendency for ALCON lenses to be more accurate. Facilities that have introduced ORA may therefore tend to choose ALCON lenses to avoid the risk of refractive error, but that in itself may ultimately benefit patients. At our clinic, when using the ORA system, we use the ALCON lens most widely used for optimization as a dummy lens, and decide the power using the difference in constants from the lens actually used, an approach to reduce refractive error even with lenses whose global optimization is not complete.
Regarding (2), anterior chamber depth and lens thickness seem important for predicting the position (depth) of the intraocular lens, so as a surgeon I find it a little disappointing that these two factors are not used as parameters for power selection in the ORA system. Anterior chamber depth in particular differs by ethnicity even within Asia, so in future I hope that, in addition to building a national database for Japan and not just a global one, it will be improved so that at least surgeon/facility optimization is possible for lenses not globally optimized. At our clinic we are examining, by multivariate analysis (multiple regression), the significance of the effects of anterior chamber depth and lens thickness on the refractive error that remains even with the ORA system, but so far the factor with the greatest effect on refractive error has been axial length. As the number of ORA cases grows, and with a shift from statistical methods to AI, the importance of overlooked parameters may become apparent.
Back to TECNIS Eyhance: occasionally people request it under the misunderstanding that it is a lens for both distance and near, but as noted above its add is only +0.5 D, so our clinic almost never recommends Eyhance to people who want to see near as well. For people with such aims and expectations within insurance-covered care, we often recommend LENTIS Comfort with a +1.5 D add, numerically three times Eyhance's near add. Also, since LENTIS Comfort appeared, we have not used TECNIS Symfony, which has almost the same add but stronger halos and glare, at all.
Since we are on the subject of add powers, finally a word about ALCON's Vivity, about which we receive many inquiries. As described previously, it has a structure using aberrations similar to Eyhance and MiniWELL, so halos and glare can be expected to be almost absent, as with monofocal lenses. Its add is reported to be about +1.5 D, so we regard it as a lens whose ease of near vision is almost equivalent to TECNIS Symfony and LENTIS Comfort (about 70 cm), with almost no photic phenomena such as halos and glare. Compared with the same company's trifocal PanOptix, with an add of +3.25 D (40 cm), care is needed not to expect excessive near vision beyond the lens's specifications.
One reason its release in Japan has been delayed seems to be that the lens, originally made and sold in a material called AcrySof, has been renewed in a new material, Clareon; at present it seems unlikely that use in Japan will begin within 2022. Whether it will be covered by the elective treatment system or by insurance is also undecided, so we will update this information in future.
2022.05.25