Dear Editor:

I read with interest the article by Knauer and Pfeiffer in Graefe’s Archive for Clinical and Experimental Ophthalmology (2008) 246:477-482 entitled “The value of vision.” The authors use, as the basis for their commentary, work that has been done to evaluate how much patients with ophthalmic diseases are concerned about their visual loss. One method of estimating this is to use the technique discussed by the authors, “the time trade-off method,” in which patients decide how many years of their life they would give up to achieve the desired outcome [6]. Knauer and Pfeiffer comment correctly that some of the studies that have been done on ophthalmic disease indicate that vision is of great importance to patients [1–3].They compare the values obtained for other conditions such as AIDS and stroke, and conclude that the relative value of the patient’s vision is truly extraordinarily great [4, 5].

The authors, however, do not consider an extremely important issue, which may well invalidate their conclusion. Time trade-off studies related to the value of vision ask the question, “What is the maximum number of years—if any—you would be willing to give up if you could have a normal vision in both of your eyes for the remainder of your life?” Note, the question has to do with recovering vision. But in contrast, in the standard time trade-off methodology patients are asked, “What is the maximum number of years—if any—you would be willing to give up if you could have perfect health for the remainder of your life?” “Vision” and “health” are not the same thing. Presumably, vision influences a person’s health. It may be that some individuals consider vision the most important aspect of their health. It may also be that some individuals consider vision an unimportant aspect of their health. But it is not proper to compare the results of those studies done by the Browns, in which they are asking patients about recovering vision, with those of the great majority of time trade-off studies, in which subjects are asked about recovering health.

As an ophthalmologist, I would love to believe that the Browns, and Knauer and Pfeiffer are correct in commenting that patients value vision ahead of being hospitalized with tuberculosis for 3 months, or having a stroke that results in a level of disability causing the person to be unable to walk and unable to wash himself or herself; however, that this is the case is speculation, and cannot be supported by comparing two different methodologies, one studying vision, and the other studying health.