PurposeTo evaluate whether the length of the inner segment ellipsoid (ISe) band can be used as a prognostic factor for disease course in retinitis pigmentosa (RP) patients with EYS mutations by observation over a period of 5 years.MethodsTwelve RP patients with EYS mutations were studied. The horizontal and vertical ISe length of the right eye was manually measured at five time points annually, using spectral domain optical coherence tomography. A regression line through the five points from baseline to the final measurement was drawn and the ratio of the length (%) at each point to the baseline length was calculated; the slope was defined as the rate of ISe shortening (%/year). The correlation between the rate of ISe shortening and age, visual acuity, and mean deviation (MD) value were evaluated. The intraclass correlation coefficient (ICC) for the measurements was calculated.ResultsThe mean rate of ISe shortening was -4.65±2.89% per year and the decline was statistically significant. The rate of shortening was significantly negatively correlated with the baseline length (P=0.046, r=0.58), but not with the baseline age, visual acuity, and MD value. The ICC (2, 1) was 0.999.ConclusionsISe of all RP patients with EYS mutations shortened during the 5 years of annual observation. The measurement of the length of ISe is a simple and convenient method with high repeatability, and the length is a sensitive prognostic factor for the rate of ISe shortening in RP patients with EYS mutations.