She had been diagnosed with cataracts ten years earlier and treated with eye drops, but as her vision worsened she decided on surgery, and she first visited us referred for surgery by the ophthalmology department of a nearby general hospital.
She is a former announcer who still works actively as a lecturer, and she wanted to see both her script at hand and the faces of students in the distance, so she wished for surgery with multifocal lenses.
At examination, owing to cataract progression and refractive changes with presbyopia, the right eye was mildly myopic (−0.625 D) and the left eye hyperopic (+2.375 D), with uncorrected distance vision of 0.7 right / 0.2 left. When we talked with her, she said that before the cataracts she had originally seen near with the right eye and distance with the left eye, so she had not used glasses.
Corneal higher-order aberrations were low and her eyes were candidates for multifocal lenses, but in that case she would probably be satisfied simply by being returned to her pre-cataract state, without going to the trouble of expensive multifocal lenses, so we proposed monovision with monofocal lenses, and she agreed. To be safe we measured preoperative uncorrected near vision, which was poor at 0.3 in both eyes, yet she said she still did not use reading glasses even for reading. At that level, all the more, we could expect better distance and near vision than before surgery even with monofocal lenses, and I was confident we could achieve a result that would satisfy her. Another reason for recommending monofocal lenses was a mild epiretinal membrane, more marked in the left eye, although foveal contour was still good.
Preoperative testing showed that the right eye's axial length was 1 mm longer than the left's, so naturally we set the right eye for near and the left eye for distance, and operated first on the left eye, which had become hyperopic, so that the difference between the eyes would not increase after surgery. Both eyes also had small pupils, so we expected greater depth of focus than usual, and to reliably secure distance in the left eye first, we set a target refraction of −0.37 D.
During left eye surgery, we used a wavefront aberrometer (ORA system), not only to reduce postoperative refractive error but also so that we could create an accurate difference between the eyes in right eye surgery, and the surgery was completed without problems.
After surgery, refraction was −0.375 D, almost zero refractive error, and she was satisfied with uncorrected distance vision of 1.2, as expected. Moreover, she said she could see near without glasses better than with her right eye, and when we measured uncorrected near vision, it was 0.7, better than expected for a monofocal lens set for distance (it varies between individuals but is usually about 0.3).
We therefore proposed modest monovision for the right eye. Measuring how much near add the left eye needed to see things at hand comfortably, we found that, partly because her right pupil was even smaller than the left, adding only about +1.0 D gave near vision of 1.0 with ease, so we set the right eye's target refraction at −1.28 D.
If lenses of exactly the same power were used in both eyes, the original difference in refraction due to the difference in axial length would be reproduced. In that case the right eye would be aimed at −3.23, suggesting that her eyes had been literal monovision with a difference of about 3.0 D, and she could probably adapt to that level. However, if she could be satisfied without such a large difference, I wanted to keep it within 2.0 D, avoiding anisometropia problems and staying within the range where glasses can be worn when needed, and set the target accordingly.
For the right eye, too, we used the ORA system and were able to create an accurate, appropriate difference between the eyes; postoperative refraction was −1.375 D, and, just as in the simulation with the left eye, the right eye's postoperative uncorrected near vision was 1.2. Furthermore, perhaps with added pseudo-accommodation from small pupils and residual astigmatism, distance vision was also better than expected at 1.0, and she was delighted that she could live without glasses for both work and daily life.
We are often asked, "How well will I see after surgery?" For people without other eye diseases aiming for exactly 0 D for distance, 1.2 can usually be expected, but uncorrected vision after setting −1.0 D of myopia cannot be predicted (usually about 0.6–0.7). This is because depth of focus differs from person to person depending on conditions such as corneal astigmatism and pupil size. So the most reliable way to find a power that will satisfy a particular person is to simulate it in that person's own eyes.
Not everyone can adapt to monovision, but for people with small pupils like her, choosing the power for each eye with staged implants that take this into account can minimize the difference between the eyes and may achieve satisfying uncorrected distance and near vision without impairing binocular function (depth perception). Refractive cataract surgery is also a chance to turn the disadvantage of a difference between the eyes into an advantage, so if you are troubled by one, please feel free to consult us.
2022.09.24