Here is your challenge. You’re operating on a patient who is highly hyperopic (wearing +6.50 OD and +7.00 OS for best distance vision for many years) and he desires to achieve a plano outcome. There is very little corneal astigmatism and your primary consideration is the spherical power of the IOL.
While the axial length in his eyes are only mildly short at 22 mm, the patient also has flat corneas with a keratometry of about 41.5 diopters bilaterally. The anterior chamber depth is more than 3 mm bilaterally, so it is relatively average and not at all shallow. The patient is very much right eye dominant and there is a history of mild refractive amblyopia OS > OD with the best-corrected visual acuity from 10 years ago showing 20/25 OD and 20/30 OS.
As you can see, the Barrett, Haigis, Hill RBF, Holladay, and Ladas AI formulas give various powers. So the questions for you are:
- Which eye gets cataract surgery first?
- What IOL power do you implant in that selected eye?
- Do you make any adjustments for the second eye and how?
Here were my decisions:
- Normally I would operate on the eye with the better visual potential first, because then the patient would be so happy that he would want the second eye even if the visual potential was not as good.
- In this case, the amblyopia OS is mild and going from a +7 refraction to plano would be a huge improvement in vision for the patient. Also, if we do cataract surgery on the left eye first, we can see our refractive results and then hone the calcs to get a more accurate result in the dominant right eye
- I did cataract surgery OS first using a +29.0 D IOL as calculated by the Ladas AI and the Hill RBF. In this hyperopic patient I want to avoid getting a myopic surprise because the patient is used to hyperopia. If the patient goes from a refraction of +7.00 and ends up even +1.00, he will be amazed at the improvement.
- After healing this eye achieved a post-op refraction of about +0.25 +0.25 x 90 which is a spherical equivalent of +0.37, which means that +29.5 D IOL would have given just about perfect plano.
- It turns out that in this case the Haigis came the closest, perhaps because of its nature where the three lens constants which help refine the prediction curve up/down (ao) as well as based on the anterior chamber depth (a1) and the axial length (a2). This allows adjustment for variable lens geometry so that a high power IOL (+30) will be adjusted differently than an average IOL power (+20) or myopic IOL power (+10).
- For the right eye, we favored the Haigis calculation and the IOL power used was +29.0 D IOL. The patient achieved an outcome of plano and was very happy.
- These results were helpful in providing more crowd-sourced data for the Ladas Super Formula AI to hone the algorithms. With the machine learning protocol, we anticipate it to become progressively more and more accurate with time.