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D.B. Denham, A. Rosen, F. Manns, J. Margolesky, J. Parel, A. Ho; Measurement of Excised Primate Lens Power in Aqueous Solutions Using Simply Modified Lensometers . Invest. Ophthalmol. Vis. Sci. 2003;44(13):244.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To non-invasively and atraumatically assess the optical power of ex-vivo human and monkey lenses in aqueous. Methods: A Humphrey Model 360 Lens Analyzer and a Nikon OL-5 lensometer and a -20D plano-concave lens forming a 9.2mm deep concavity filled with distilled water or DMEM were used. The sample immersed in the cell is covered with a thin cover slip providing an optical flat upper surface, eliminating fluid/air interface meniscus. The fluid filled lens is held in various adapter rings that securely locate it over the lensometers optical centers. Seven glass plano-convex lenses immersed in distilled water were used for calibration. Their optical power in water was calculated using known radii of curvature and indices of refraction. In a pilot study 3 human and 8 cynomolgus crystalline lenses were measured. Lensometer readings of the sample were adjusted for the –7.0D produced by the fluid filled cell. Results: The calculated power in water for the seven test lenses used ranged from +7.92D to +28.1D. The measured power correlated well with the calculated power when a linear curve fit passing through the origin was derived. The Nikon slope was 0.9999 with an R2 = 0.9999 and the Humphrey slope was 1.0145 with R2 = 0.9978. Neither instruments worked well with human cadaver lenses due to the cloudiness of the cateractous material. Both instruments could be used on small 7mm monkey lenses (range 28.6 to 32.9D). The Nikon is limited to an absolute maximum reading of +32D (+25D plus +7D) and the Humphrey to +57D (+50D plus +7D) in water, but the linear calibration range of the Humphrey only extends to +27D. Tests with a more powerful negative lens (-40D) in the test cell proved unsuccessful. Conclusions: Non-human primate crystalline lens power can be estimated using easily modified conventional instruments fitted with a special fluid filled cell. The Nikon OL-5 has the theoretical advantage of being used on smaller equatorial diameter monkey lenses, since only a single test beam passes through the center of the lens. Used in the standard spectacle mode the Humphrey instrument projects four test beams through the lenses at a 5mm diameter . Measurements on human tissue will require clear lenses from younger subjects.
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