April 12, 2019 Conference
Special considerations are taken into account when planning for cataract surgery in a patient with keratoconus. In mild keratoconus, one must be aware of the implications previous or future collagen cross linking can have on the cornea. Aiming for mild myopia is preferred in these patients given the hyperopic shift which occurs with corneal flattening after crosslinking. In a patient with stable and mild keratoconus who will not need crosslinking, a toric lens implant can be considered if: 1.) spectacle refraction was stable and satisfactory prior to cataract development; 2.) biometry is reliable and consistent with multiple modes of measurement; 3.) the patient will not wear a rigid contact lens in the future. An extended depth of field or multifocal lens implant is inadvisable in patients with corneal ectasia of any degree.
Moderate keratoconus patients should be aimed for moderate myopia given a more posterior effective lens position than expected based on IOL calculation formulas. In addition, fitting a rigid myopic lens is easier and better tolerated compared to a rigid hyperopic lens. It is ideal, but not always possible, to have the patient suspect rigid lens use several weeks prior to biometry.
In those with severe keratoconus (candidates for PKP or DALK), keratoplasty would ideally be performed prior to phacoemulsification. This will allow for more accurate lens calculations and a better refractive outcome. If the cataract surgery is to be done prior to, or in tandem with, keratoplasty, it is recommended to power the lens implant with an arbritrary K value of roughly 44D rather than using the Ks from the steep, ectatic cornea. This will prevent high hyperopia following keratoplasty. Intraoperatively, the peripheral cornea can be thin and the view can be poor, thus secure wound closure and the use of capsular staining can be helpful.