How do you determine whether to proceed with topography-guided PRK, lamellar keratoplasty, or a full-thickness transplant in patients with irregular astigmatism and corneal scarring?  

Start with a rigid gas permeable refraction. If the vision can be improved to a satisfactory level, then something like topography guided PRK could be considered, or simply fit the patient in a RGP/Scleral lens. If the vision is still not adequate a lamellar keratoplasty can be considered. Although ...