Which fundus lens has an approximate magnification of 1x when used with Slit Lamp?

Which fundus lens has an approximate magnification of 1x when used with Slit Lamp?

• A. 60D
• B. 78D
• C. 90D
• D. 100D

Answer: (A)

In slit-lamp fundus viewing, magnification depends on the lens power and how the eye-to-lens setup is arranged. The 60D lens has the longest focal length among the commonly used slit-lamp condensing lenses, so at the standard working distance it produces a retinal image that appears about the same size as the actual retina—roughly 1x magnification. The higher-power lenses (78D, 90D, 100D) have shorter focal lengths and, in the same setup, yield a retinal image that is smaller in angular size (magnification less than 1x) even though they can give a brighter or more magnified view of a smaller area. So, for an approximate 1x magnification, the 60D is the best choice.

In slit-lamp fundus viewing, magnification depends on the lens power and how the eye-to-lens setup is arranged. The 60D lens has the longest focal length among the commonly used slit-lamp condensing lenses, so at the standard working distance it produces a retinal image that appears about the same size as the actual retina—roughly 1x magnification. The higher-power lenses (78D, 90D, 100D) have shorter focal lengths and, in the same setup, yield a retinal image that is smaller in angular size (magnification less than 1x) even though they can give a brighter or more magnified view of a smaller area. So, for an approximate 1x magnification, the 60D is the best choice.