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To the Editor.
—I agree with Dr. Burian's suggestion that two wavelengths are useful in separating rod from cone function during dark-adaptation as he and several others have been doing for some time. This is not the point of my paper, however. What I have tried to show was how it is possible to map the local sensitivity of the cone and rod systems independently at different points in the dark-adapted retina. This is another matter from studying how rods and cones change their sensitivity during dark-adaptation. This is why the target size as well as the wavelength of the test stimuli is critical for clinical as well as any other sort of application. Using a larger size (certainly larger than one degree) or a shorter wavelength than I use to test for cones will not give cone function at all but show only the rods everywhere in the retina.
Gunkel RD. TECHNIQUE FOR RETINAL SENSITIVITY TESTING-Reply. Arch Ophthalmol. 1967;78(5):692. doi:10.1001/archopht.1967.00980030694024