RESPONSE LETTER TO DR. GAYNES

Abstract

To the Editor: We thank Dr. Gaynes for taking interest in our study to understand the role of vision in one's ability to take medications. We agree that taking medications is a complex instrumental activity of daily living (IADL) that likely relies on components of vision. The major, and largely unsubstantiated, premises of Dr. Gaynes' letter, that the Hopkins Medication Schedule (HMS) did not adequately measure ability and that vision was poorly measured, expose fundamental misunderstandings regarding (1) the import of the HMS and its application here and (2) vision assessments and interpretation. Regarding the former, Dr. Gaynes fails to distinguish between ability and adherence, further reinforcing the importance of methods that differentiate these. We refer him to the HMS validation paper1 to understand the import of developing a standard, objective measure of one's ability to understand and implement a medication prescription, independent of other determinants of adherence. Medication-taking ability was assessed using an ecologically valid, standardized instrument that mimics the commonly used medication organizer with a simple medication regimen. The HMS-based measure of ability incorporates correctness and speed of task completion, as do many measures of functional or IADL ability; faster was not assumed to be better. With regard to vision assessments, we are confident in the standardized, validated methods developed by vision experts and employed in the Women's Health and Aging Study (WHAS) II.2-4 Although near acuity was not evaluated, it is well known that distance and near acuities are correlated,5, 6 and the observed association between distance acuity and ability remains an important finding. Nevertheless, we agree that the association with near visual acuity may be informative. We disagree with Dr. Gaynes' statement that a modified Pelli-Robson contrast at closer distance would have been more meaningful. Test distance over the range in question does not affect Pelli-Robson contrast sensitivity.7 The Mars Letter Contrast Sensitivity he recommended was not available at the time of WHAS II, but a recently published validation showed excellent agreement between Mars and Pelli-Robson contrast sensitivities.8 Dr. Gaynes' statements regarding stereopsis were based on a study of young participants (mean ages 29, vs 77 in WHAS II) with normal stereoacuity (mean 17.6 vs 100 seconds of arc);9 those findings should not be generalized to older persons with impaired stereoacuity. In older adults, stereopsis has been associated with activity of daily living disability and function.10, 11 Regarding dexterity and “alertness,” as we described, testers assisted participants opening containers, thus limiting contamination by dexterity problems. Adjusting for hand osteoarthritis did not substantially change our findings. A previous study suggesting that vision might facilitate adaptations to age-related functional and cognitive declines12 was the impetus for including interactions between vision and cognition. In summary, Dr. Gaynes' comments extend our line of inquiry by positing that the significance of near visual acuity to medication taking should be measured. We welcome a formal test of this hypothesis, because this is the means by which scientific advances are made and translated into clinical practice for maintenance of independent function. Financial Disclosures: The research referred to in this article was supported by National Institute on Aging Grant R01 AG11703–01A1 and by National Institutes of Health (NIH)—National Center for Research Resources, Outpatient General Clinical Research Center Grant RR00722. Dr. Griswold and Dr.Windham were supported by the NIH T-32 Training Grant entitled “The Epidemiology and Biostatistics of Aging” when this study was conducted. Author Contributions: Windham: study concept and design, data analysis and interpretation, manuscript preparation, letter to editor draft and revision. Griswold: study design, data analysis and interpretation, manuscript preparation, letter to editor revision. Fried: WHAS II principle investigator, study concept and design, acquisition of subjects, data interpretation, manuscript editing, letter to editor revision. Rubin: study design, data interpretation, manuscript editing, letter to editor revision. Xue: data interpretation, manuscript editing. Carlson: study concept and design, data interpretation, manuscript editing, letter to editor revision. Sponsor's Role: None.