How do you approach IOL calculations and selection in patients with keratoconus based on disease severity?

Lens selection assuming stable KCN and no plan for a transplant:

1. Symmetrical astigmatism and they don't want to wear CL after surgery? Can consider a toric lens.
2. Symmetrical astigmatism and they are okay with continuing RGP/sclerals? Monofocal aberration-free lens.
3. Asymmetrical astigmatism and wanting some glasses independence? Pinhole IOL (for non-dominant eye, aim -0.75)

I generally prefer putting in an aberration-free lens and aiming slightly minus.

Formulas: I like using the Barrett True-K formula.

Lenses: I do not recommend multifocals or extended depth of focus. The keratoconus already induces optic aberrations, so placing those lenses might add to it.

If they are getting PK, I like to wait for the PK first, and we can do the cataract later. The K values might change a lot after the transplant.

If they are not getting a PK, the RGP is the key.

If they don't want to use RGP and have regular astigmatism in the center 2.5mm, I would consider using a toric IOL. I consider the measures from the optical biometer to calculate the IOL.

If they consider using RGP or have irregular astigmatism, I will use a simple monofocal IOL. The tear meniscus under the RGP will correct corneal astigmatism...

I usually do these with the consultation of our cornea and contact lens colleagues.

Key question. What is the likelihood of PK? If no PK, are they planning to wear CL post op?

If they are likely getting PK after CE, then I get a reasonable K value post-transplant from our cornea service, or have them perform CE surgery at the same time as PK.

If there are no plans for PK and the patient will be wearing a CL post-op, then I usually leave the patient about -2 to ease CL fabrication and fit.

Not a great answer, I suppose, but that’s my approach.

If I have historical refractive information on the patient and refraction is stable, I would consider a toric lens. If in need of a PK, that first. Wait 5-6 months before cataract extraction. Otherwise monofical spherical lens.