She first visited us with a referral letter from her previous doctor for consultation about cataract surgery, and wished to have surgery with PanOptix or TECNIS Synergy if she was a candidate. She was highly myopic, but her vision loss was caused not by nuclear cataract but by cortical opacity extending into the pupillary area, and corrected visual acuity had fallen to about 0.6 in both eyes, so we felt she could have surgery whenever she wished.
She also had constant dry eye symptoms and was using eye drops such as hyaluronic acid preparations, so we were concerned about corneal higher-order aberrations. In corneal topography such as the OPD-Scan III results above, corneal astigmatism was very strong, but the Fourier analysis by component shown below indicated that it consisted mainly of regular astigmatism, which can be corrected with a toric lens, and higher-order aberrations were low, so we diagnosed her as a candidate for multifocal lenses if she wished.
She wore soft contact lenses and was used to wearing reading glasses over them, so she wished for a monofocal lens set for distance if she chose monofocal. However, her corrected near visual acuity had also fallen to 0.6, so we told her that even with multifocal lenses there would be almost nothing worse than before surgery, and gave her time to consider.
After discussion, since she has no occasions to drive and, being highly myopic from the start, her near working distance was relatively short, she agreed to surgery with the toric TECNIS Synergy, whose near focal distance is close. The left eye, with the more advanced cataract, was scheduled first, and because of her work the right eye was scheduled one month later. A long interval between the two surgeries means anisometropia in the meantime, making it hard to fit glasses and difficult to get by; contact lens wearers like her, however, can usually live without problems by wearing a contact lens in the other eye.
There was also mild corneal opacity and visibility during surgery was somewhat poor, but left eye surgery was completed without problems. Although she was highly myopic, her axial length was only about 25 mm; her high myopia was due to corneal power exceeding 45 D (normally about 43 D). Eyes with such unfavorable proportions are prone to refractive error, so here too we determined the lens power using the ORA system, an intraoperative wavefront aberrometer. For TECNIS Synergy, the manufacturer recommends using the lens power whose predicted refraction is closest in absolute value to 0.00 D. In her case, trusting the preoperative test results, the recommended power from the preoperative calculation on the left of the figure below would have been a 12.5 D lens targeting +0.11 D. The intraoperative measurement, however, recommended the 13.5 D lens targeting −0.55 D, which we had prepared in advance as a backup. Measurement results cannot be trusted completely, and eyes with high corneal power usually tend to shift toward near, so choosing a lens targeting −0.55 D was a difficult decision; but considering our experience and the tendencies of the ORA system, we finally used the 13.5 D lens.
We used to simply implant the lens decided before surgery, but since we began intraoperative measurement, there are more things to select and decide in real time during surgery, so surgery inevitably takes longer. We believe, however, that performing more precise surgery matters more. Especially with toric lenses, not only the lens power but also the cylinder power and axis, fine adjustment of the axis after lens insertion, and remeasurement for confirmation are needed, so in some cases the time spent measuring is almost the same as the time spent actually operating. Because we perform intraoperative wavefront aberrometry in every case, we limit the number of surgeries per day; we apologize that, as of March 15, 2023, there is a waiting period of about three months until surgery.
After left eye surgery, neither the refractive error nor the astigmatic axis shift we had feared occurred, and she was delighted with good uncorrected vision of about 1.2 at both distance and near. Had we trusted only the preoperative test results, the eye would probably have become quite hyperopic, so in this case too the ORA system helped us. For the month until right eye surgery she lived, as planned, with a contact lens, and we planned to adjust for any dissatisfaction with the left eye at the time of right eye surgery.
At the preoperative visit for the right eye, she wished for a target the same as the left eye or slightly toward distance. Artificial lenses are usually made only in 0.5 D steps, so the two eyes cannot be matched down to the decimal places. Even if the same power is requested, a difference of less than 0.5 D between the eyes will always remain. It is quite hard, and probably difficult, for patients to hear intraoperative measurement results under the special circumstances of surgery and immediately make an appropriate decision, so at our clinic we ask patients to decide in advance whether they would choose a lens leaning toward distance or toward near depending on the intraoperative results.
For the right eye, as for the left, we used the ORA system to determine lens power and cylinder power, set the axis, fine-tuned it and remeasured for confirmation, and the surgery was completed without problems.
After surgery, as she wished, measured refraction was 0.25 D more toward distance than the left eye, and as expected she achieved uncorrected vision of 1.2 at both distance and near. She was very satisfied that she could see well without glasses, with no problems at all, for her hobbies of singing and going to the theater and at the distances needed for cooking at work.
Presenting cases like this may give the mistaken impression that the ORA system is all-powerful, but it is a tool to be used as a reference after thoroughly analyzing preoperative test results and understanding the tendencies, or characteristics, of its measurements; I feel its results still cannot be trusted completely. As the manufacturer's naming suggests, it is a device for "VERIFY" only. The ORA system uses AI to calculate the recommended lens power from preoperative axial length, corneal power, intraoperative total ocular aberration, and the SF (surgeon factor: a constant specific to the lens and surgeon). It depends on the patient, but among these, the least stable, i.e., least reproducible, item seems to be corneal power. Values differ even for the same eye from day to day, depending on the tear film and so on, but I think the biggest problem is that the measurement zone differs from device to device. Current prediction formulas, including Barrett Universal II, use the value for the central 2.5 mm of the cornea, whereas Verion, used with the ORA system, measures 2.4 mm, and ARGOS an even narrower 2.2 mm. As a result, Verion and ARGOS tend to measure stronger corneal power than the central 2.5 mm value used in prediction formulas. Adjusting the SF may ultimately cancel out the difference, but for consistent optimization I would like measuring devices and zones to be standardized, or optimization to be done for each device.
That turned into a bit of a complaint, but at our clinic, multiple regression analysis of factors affecting the size of refractive error with the ORA system has shown that, besides axial length, the larger the difference between corneal power at the central 2.5 mm and 2.4 mm, the larger the refractive error with the ORA system. Since then, we have used a regression formula that takes this difference into account to determine the optimal lens power, in an effort to reduce refractive error even slightly.
Some patients think they must decide the lens type and target refraction at the first visit, but that is not the case at all. Especially for surgery on both eyes, any shortcomings after the first eye can be made up for in the fellow eye. With a multifocal lens, I think it is fine to start by aiming for emmetropia (0 D), where the lens's specifications are most likely to be realized. With a monofocal lens, I recommend first choosing a power that reliably covers the distance you most want to see without glasses, then choosing the fellow eye's power by comparing it with the vision in the operated eye. Individual conditions such as corneal astigmatism and pupil size, which are said to affect pseudo-accommodation, differ from patient to patient, so results may be better or worse than the lens specifications or postoperative refraction would suggest. Our clinic takes measures and makes preparations so that we can respond flexibly to patients' wishes right up to the day of surgery, so please feel free to consult us.
2023.03.15