The lacrimal lens as an assessment factor in hard contact lens fitting.
The fitting of hard contact lenses relies primarily on the evaluation of the findings of 'K' readings, the fluorescein pattern of the tear configuration and the interpretation of the lens movement upon blinking and the lens position after blinking. All of these methods have some disadvantages in the evaluation procedure: (a) keratometer readings measure cornical radius in a small and restricted area of the central cornea not in the larger area to eventually be covered by the lens (Bennett and Rabbetts, Clinical Visual Optics. Butterworths, London, UK, pp. 420-421, 1984); (b) the fluorescein pattern is sometimes unreliable especially in the presence of excessive tear flow; (c) lens movement, arguably the most reliable of evaluation methods, nonetheless requires some alternative back-up technique. This presentation outlines the possibility of utilising the lacrimal lens as a useful additional procedure to the above when prescribing a lens curvature of choice. It should be pointed out that the technique discussed refers to spherical or near spherical corneas.
Department of Optometry, University of the North, Sovenga, South Africa.
M
M
Gowans
D003261:Contact Lenses; D003315:Cornea / Q000033:anatomy & histology; D006801:Humans; D008433:Mathematics; D055095:Optics and Photonics; D009907:Optometry / Q000379:methods*; D013666:Tears