王藹侯2006-07-262018-07-122006-07-262018-07-121999http://ntur.lib.ntu.edu.tw//handle/246246/26706Purpose. Conventional photorefractors applying either camera or video have fixed distance between the viewing line and the light source and read the refraction from the size of the crescent. Since the relationship between the crescent size and the refraction is not linear and the resolution at higher refractive error is poor, a hand-held photorefractor was introduced which employed fixed crescent:pupil ratio as endpoint and read the refraction from the varying distance between the eye and the light source. The relationship between the distance and the refraction is linear. Methods. For ‘axial’ myopia and hyperopia, a simple formula holds that do = Ratio‧Pu‧lo‧R where do is the distance between the eye and the light source; Ratio is the non-crescent:pupil ratio; Pu is the pupil diameter; lo is the test distance and R is the refraction relative to the vergence of the test distance. A design of hand-held photorefractor, similar in shape with direct ophthalmoscope and retinoscope, was proposed that by sliding the Ai-Hou Wang light source up and down and looked through a fixed viewing hole for a fixed crescent:pupil ratio, the refraction could be read from a linear scale with good resolution. Oblique astigmatism could be read simply by aligning the instrument with the oblique crescent, no need to rely upon complicated calculation. Results. With random combination of spherical and cylindrical lenses in front of a model eye I read the refraction blindly with a prototype of this hand-held photorefractor. The result was satisfactorily accurate. Conclusions. A practical hand-held photorefractor was designed, with which the refraction could be read on a linear scale with good resolution, and the axis of oblique astigmatism could be determined by simply aligning the instrument with the tilted crescent.application/pdf254776 bytesapplication/pdfzh-TW國立臺灣大學醫學院眼科journal articlehttp://ntur.lib.ntu.edu.tw/bitstream/246246/26706/1/882314B002374.pdf