A New Fundus Camera Technique to Help Calculate Eye-Camera Magnification

Michael G. Quigley
2003 Archives of Ophthalmology  
Objective: To find a simple means for calculating eyecamera magnification to permit estimation of true retinal object size from a retinal photograph. Methods: The position of the focusing knob on 3 different retinal cameras (TRC-50F and TRC-50X; Topcon America Corp, Paramus, NJ; and the CR6-45NM Nonmydriatic Retinal Camera; Canon Inc, Tokyo, Japan) was measured during optic nerve photography and correlated with the refractive error, or spectacle refraction, of the subject (N= 11 for each
more » ... 11 for each camera). Results: A strong correlation was found between focusing knob position and spectacle refraction for each of the 3 cameras tested (r=0.96, r=0.99, and r=0.97, respectively). Conclusions: The focusing knob position reflects the spectacle refraction of the eye being photographed, and spectacle refraction is known to correlate well with eyecamera magnification. Therefore, focusing knob position can be used to help calculate eye-camera magnification and, hence, true retinal object size. Clinical Relevance: The true size of the optic nerve head is important for the diagnosis of glaucoma from a retinal photograph. This technique is a simple means to calculate optic nerve head size, which may be especially useful in mass retinal photographic screening programs.
doi:10.1001/archopht.121.5.707 pmid:12742849 fatcat:ueznqhftxfeedo2srvnuldjudu