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He investigated the optical constants of the eye, measured by his invention, the ophthalmometer, the radii of curvature of the crystalline lens for near and far vision, explained the mechanism of accommodation by which the eye can focus within certain limits, discussed the phenomena of colour vision, and gave a luminous account of the movements of the eyeballs so as to secure single vision with two eyes.

Helmholtz in his “Ophthalmometer” has employed Clausen’s principle, but arranges the plates so that both move symmetrically in opposite directions with respect to the telescope axis.

Associated words: optics, optician, ocular, oculary, oculate, oculifonn, ophthalmology, ophthalmologist, ophthalmic, optometry, ophthalmostat, optometrist, chatoyant, chatoyment, cynosure, orbit, strabismus, rheum, ophthalmoscope, ophthalmoscopy, astigmatism, optography, blear, blear-eyed, bleary, ophthalmometer, orbital, orbitary, amaurosis, ocellated. eyebrows, n. pl. supercilium.