a lens with fine parallel lines (almost invisible striations) across its width, used in various vision tests; for example, to test suppression and abnormal retinal correspondence. [B. Bagolini (20th century), Italian ophthalmologist]
Displacement of the crystalline lens from its normal position in the eye. Lens dislocation is almost always caused by an injury that ruptures the fibres connecting the lens to the ciliary body. In Marfan’s syndrome, these fibres are particularly weak and lens dislocation is common.A dislocated lens may produce severe visual distortion or double vision, and sometimes causes a form of glaucoma if drainage of fluid from the front of the eye is affected. If glaucoma is severe, the lens may need to be removed. (See also aphakia.)... lens dislocation
lenses that are specially designed to give clear images, eliminating the coloured fringes that are produced with ordinary lenses (caused by splitting of the light into different wavelengths and hence its component colours). Such lenses are useful in scientific instruments, such as the eyepieces of microscopes.... achromatic lenses