Editor,—We read Tanner et al's paper on the predictive value of vitreous pigment (Schaffer's sign) for retinal breaks in posterior vitreous detachment1 with great interest. Based on their figures, patients who have a negative Schaffer's sign had a 1% chance of having a retinal tear or hole and a 0.5% chance of having a lesion where prophylaxis was thought to be appropriate. Thus, Schaffer's sign has a negative predictive value of 99% in their series. They go on to recommend that if vitreous pigment is present then the patient should be referred for urgent vitreoretinal opinion while those with no pigment should be referred on a less urgent basis.

We would like to put these findings in perspective. The incidence of retinal breaks in …