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G.A. Zikos, Y. Han, A. Selenow,, K.J. Ciuffreda, S. Ali; AN OBJECTIVE TECHNIQUE TO ASSESS THE FUNCTIONAL ENVELOPE OF VISION IN PALS . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2540.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Progressive addition spectacle lenses (PALs) are complexly–designed ophthalmic lenses that have, non–uniform optical blur present, which reduces the usable lens area. To maintain the line–of–sight within a zone of acceptable clear vision, one is required to execute frequent and precise eye and head movements. We have developed a new, objective technique to assess the precise point on a spectacle lens (i.e., the point–of–regard, or POR) that the line–of–sight intersects during a visual task. The locus of such points operationally defines the functional envelope of clear vision. Methods: Two–dimensional (horiz. and vert.) recordings of POR, eye, and head movements were obtained using our newly reconfigured eye/head movement system (ISCAN, video; POLHEMUS, electromagnetic, respectively). Healthy presbyopic subjects (n=3) were asked to read and maintain clear adult–level reading materials placed in primary position along the midline at a distance of 64 cm. binocularly, simulating PC screen reading. Relatively wide (30o Horiz.), low–contrast (40%), 9 point text (20/32 equivalent) was used to force both eye and head movements during reading. Reading was performed with a single vision lens and two PALs with different intermediate zone widths (PAL I =8.30, PAL II=7.73 mm). The POR–based functional envelope was objectively determined and the horizontal component compared with the optically–predicted usable zone based on the criterion of 0.75D of unwanted astigmatism present. Results: The POR–based functional intermediate zone region was always much larger for SVL versus PALs. The horizontal component of the functional envelope for the SVL was 2.35x larger than for PAL I, and 2.44x larger than for PAL II. The width of the functional envelope of vision for the PALs was 38% smaller in PAL I and 34% smaller in PAL II than predicted by an optically–calculated intermediate zone width based on unwanted astigmatism. Conclusions: We have developed a new way of objectively and quantitatively defining the envelope of functionally clear vision through a spectacle lens based on recordings of POR performed under naturalistic reading conditions. This method can be used to provide valuable information to improve PAL lens design by identifying the functionally important areas of a lens for a range of tasks at all distances. While our findings demonstrate large differences between SVL’s and PAL’s, the differences between PAL’s were small but consistent with their intermediate zone width differences. Thus, the results from our new functional test may be used to redefine optical industry standards.
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