Despite this short-coming, excellent longitudinal studies are being conducted and are slowly emerging in the literature. In the June issue, Shirayama-Suzuki and colleagues1 examined keratoconus progression in the fellow eye in unilateral keratoconus patients over the course of 6 years. The fellow eyes were included if they had no slit-lamp signs of keratoconus or deterioration of spectacle-corrected visual acuity. The authors found that just over 20% of the fellow eyes progressed to clinical keratoconus with evidence of increased asymmetry, spherical equivalent and higher-order irregularities, which they documented with topographic indices and Fourier analysis. As they note, keratoconus is a slowly progressing disease, and therefore it is likely that a longer follow-up would result in more of their cohort progressing to clinical keratoconus.