du Toit R, Soong K, Brian G, Ramke J (August 2006). "Quantification of refractive error: comparison of autorefractor and focometer". Optom Vis Sci. 83 (8): 582–8. doi:10.1097/01.opx.0000230270.39804.54. PMID16909083.
du Toit R, Soong K, Brian G, Ramke J (August 2006). "Quantification of refractive error: comparison of autorefractor and focometer". Optom Vis Sci. 83 (8): 582–8. doi:10.1097/01.opx.0000230270.39804.54. PMID16909083.