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O. Overbury, C. Collin, W. Wittich, L. Ziebell; Nonlinear Relationships Between Letter Acuity and Face Acuity: Implications for Assessment of Visual Function. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5518.
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Face recognition difficulties are a common complaint among visually impaired individuals, yet there exists no widely-recognized standardized instrument for testing face recognition acuity. To fill this gap, we have developed a set of Face Acuity Charts (FACs). The FACs are very similar to ETDRS letter charts, except they contain face images instead of letters. This design makes the task easy to administer and it is familiar to those being tested.
Two sets of 3 FACs (OD, OS, OU) have been designed: One set has pictures of faces that include hair and ears, the other has these features cropped out, leaving only the face itself. All charts are based on a set of 10 arbitrarily selected faces, 5 male and 5 female. These are organized on the FACs in a similar fashion to the 10 letters of the ETDRS charts. To establish some preliminary norms, we tested a sample of 58 university students on the FAC and the ETDRS. All participants had normal colour vision (HRR pseudoisochromatic plates) and acuity of 20/20 or better with correction. To obtain a range of acuity levels, myopic participants were tested both with and without correction.
Our results show that face acuity (F) rises exponentially with letter acuity (L). This is true both for the FACs with hair (F = 6.26e 0.0282L; R2 = 0.61) and the FACs without hair (F = 3.51e 0.0312L; R2 = 0.54). As the charts contains only Caucasian faces, we analyzed the results in terms of the other-race effect, finding that non-Caucasian recent immigrants had poorer performance than others.
These data show that it is not advisable to make a straightforward one-to-one prediction of face recognition capacity from letter chart measures. Consequently, a separate measurement instrument for face acuity is necessary. The data also suggest that relatively minor deficits in letter acuity can be associated with stronger deficits in face acuity. Further research, using a sample more representative of the general population, is planned. This will be aimed at perfecting the design of the charts and, ultimately, at establishing norms for the FAC in order to make it useful as a clinical tool.
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