An optician recommended she see an eye doctor because of poor vision in the right eye that could not be corrected, so she first visited us. As for the cataracts, nuclear hardness was not even grade 1–2, and there was cortical opacity, but on slit-lamp examination there seemed to be no marked difference between the eyes that would explain the difference in vision.
We therefore suspected reduced vision from a disease other than cataract; the retina and macula were normal, and there was mild thinning of the retinal nerve fiber layer, worse in the right eye, so we also investigated neurological conditions such as glaucoma and optic neuritis, but all were normal. On slit-lamp examination both eyes had cataracts, but we found no difference between the eyes certain enough to explain the difference in vision, so we hesitated to recommend surgery on the assumption that cataract was the cause. We therefore decided to evaluate the difference in cataract between the eyes objectively with Nidek's OPD-Scan III, a wavefront analyzer we have had since opening.
The OPD-Scan III is an instrument that can assess aberrations, simply put, minute differences in refractive power, by location; we perform it free of charge, especially for people wishing for multifocal lenses, to judge candidacy by assessing irregular corneal astigmatism and so on. It is a very useful instrument and, I think, essential for surgery requiring the precision of multifocal lenses, but unfortunately insurance currently covers it only for people with intraocular lens decentration.
The figures below are her preoperative OPD-Scan III results with dilated pupils. Please compare the contents of the left eye's ☐ and the right eye's ☐.
Left eye: preoperative OPD
Right eye: preoperative OPD
These show how a black dot entering the eye spreads and blurs at each part of the eye. First, the middle column shows the blur at the cornea: in both eyes the black dot inside the ☐☐ is not very blurred. Spherical aberration (☐) is also small, so at this point we can assess that she is likely a candidate for multifocal lenses, and that little vision loss occurs at the corneal surface. Next, the rightmost column shows blur arising internally ("Internal"), that is, blur mainly from the crystalline lens = the cataract. At the lens, the black dot in the right eye's ☐ is very blurred compared with the left eye's ☐. In other words, light entering the eye is scattered mainly by the lens = cataract, which is very likely causing the reduced vision. The leftmost column shows the blur of the whole eye, combining cornea (middle column) and lens (right column), so it simulates how she sees. Here too the black dot in the left eye's ☐ is clean and almost unblurred, whereas the right eye's ☐ is very blurred, and the cause of vision loss from that blur was predicted to be mainly the lens = cataract in the rightmost column. The internal higher-order aberration values at far left, 0.094 in the left eye versus 0.646 in the right, an order of magnitude larger, also suggest reduced vision in the right eye due to cataract; and since corneal higher-order aberrations were small in both eyes, she was considered a candidate for multifocal lenses if she wished.
We showed her these results and explained that although slit-lamp examination showed no obvious difference in cataract between the eyes, the cause of the reduced vision in her right eye was probably increased internal aberrations = cataract, so if she wanted her vision improved, though it was not urgent, surgery was the only option.
After discussion she wished for cataract surgery with multifocal lenses; she does office work, usually wears multifocal contact lenses, and wished to live without glasses, so we recommended TECNIS Synergy, which emphasizes near vision.
TECNIS Synergy is a continuous-focus multifocal lens that sees from about 35 cm near to distance, but photic phenomena such as halos and glare are somewhat strong, and it is somewhat sensitive to astigmatism, so its multifocal function is said to work best when the lens is chosen to keep postoperative astigmatism within 0.75 D. The right eye had about 0.72–0.78 of corneal astigmatism, depending on the measurement method, a borderline amount, but the axis was somewhat oblique (25–30 degrees), and oblique astigmatism readily causes poor vision, so for a better result the surgery was done with toric Synergy.
Surgery with a toric lens is like fitting the lens's flatter meridian to the cornea's steeper one, so the angle at which the lens is placed is very important. The target angle can be calculated online by entering the corneal measurements and the lens power to be used, as shown below.
The corneal contour of course also changes with the surgical incision, and that change is built into the calculation. For her, the results showed that with the non-toric Synergy ☐DFR00V, +1.02 D of astigmatism would remain; with the 1.5 D toric Synergy ☐DFW150, +0.07 D, almost zero; and with the toric Synergy ☐DFW225, +0.41 D of new astigmatism would arise in the reversed direction. Naturally we operated with ☐DFW150, inserted at an angle of ☐25 degrees, and the postoperative result is the OPD-Scan III below.
Right eye: postoperative OPD
Look first at the top figure in the rightmost column: the ochre dashed line C is the corneal astigmatic axis, and the light-blue dashed line I is the internal, that is, the lens's, astigmatic axis. As the astigmatism data in the ☐ at lower right show, the cornea at 118 degrees and the lens at 28 degrees are exactly perpendicular, 90 degrees apart, so the corneal astigmatism of −0.79 D is canceled by the intraocular lens's astigmatism of −0.73 D, giving a total ocular refraction of 0.00 D with zero astigmatism.
With surgery as described above, vision of right 0.09 (0.4) and left 0.1 (1.0) at distance and right 0.3 (0.4) and left 1.0 (1.2) at near before surgery became a very good 1.2–1.5 uncorrected at both distance and near in both eyes after surgery. She had been myopic at about −3.0 D before surgery (near focal distance about 30 cm), so I worried that her near vision might end up worse than before, but she said office work became easier after surgery and driving was no problem, and she was very satisfied with life without glasses.
TECNIS Synergy is distinctive as a lens that sees near at 30 cm; Johnson & Johnson is due to release TECNIS Eyhance, a new non-diffractive low-add lens with an add of about +0.5 D, as a monofocal lens. Alcon also seems set to release AcrySof IQ Vivity, a non-diffractive EDOF (extended depth of focus) lens using aberrations, with an add of about +1.5 D. Both have weak near adds, but photic phenomena such as halos and glare are expected to be as few as with monofocal lenses.
So in future lenses may polarize into two types, those with halos and glare but good near vision, and low-add ones weak at near but with few halos and glare like monofocals; we will keep updating information so that we can recommend lenses suited to each patient's wishes.
2021.06.12