Effect Of Upper And Lower Lids On Translation Of Rigid Bifocal Lenses.

Segmented or alternating vision bifocal contact lenses require lens translation. This vertical movement can be obtained mainly by a combination of movements of the globe and resulting lid positions. The initial accepted theory involved the lower lid pushing the contact lens upward upon downward gaze (reading position) thus placing the nearpoint portion of the lens in the line of sight. The latest theory was proposed by Irvin M. Borish, O.D., in· l 985. Borish investigated and concluded that the lower lid theory, which essentially assumes no change in lower lid position with downward gaze, is erroneous. Borish concluded, based on a number of photographs with a variety of lenses with bifocal designs, except in cases of very high
lower lid positioning on the cornea, that contact lenses are appropriately positioned in the reading position more often by upper lid grasp of the lens than by interposition of the lower lid margin against the bottom of the lens. In this study, I have investigated vertical movement of two types of rigid contact lenses upon downward gaze: prism ballasted and minus
carrier lenticular lenses, in order to prove or disprove that vertical translation of a contact lens is produced via upper lid action. Theoretically, the prism ballasted lens should, in effect, be moved by the lower lid upon which it rests and the minus carrier lenticular would be grasped and moved about by the upper lid.