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Peripheral light focusing as a potential mechanism for phakic dysphotopsia and lens phototoxicity
Author(s) -
Kwok L. Stephen,
Daszynski Damian C.,
Kuznetsov Valerian A.,
Pham Therese,
Ho Arthur,
Coroneo Minas T.
Publication year - 2004
Publication title -
ophthalmic and physiological optics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.147
H-Index - 66
eISSN - 1475-1313
pISSN - 0275-5408
DOI - 10.1111/j.1475-1313.2004.00181.x
Subject(s) - optics , lens (geology) , cornea , intensity (physics) , phototoxicity , curvature , materials science , light intensity , physics , chemistry , mathematics , geometry , in vitro , biochemistry
Our aim was to examine secondary image formation in the anterior segment caused by peripheral light focusing (PLF) in the human cornea, and in particular the crystalline lens. Non‐sequential ray‐tracing (OptiCAD) was applied to an anatomically based human eye model, which incorporates a gradient index crystalline lens. For analysis of the limbal effect, we varied the incident angle from 100 to 122°, while for the crystalline lens effect, the incident angle was varied from 60 to 90°. The corneal shapes studied included central radii from 7.4 to 8.2 mm with a range of shape factors. In each case, we computed the peak and average intensities, and the area of exposure at the limbus or lens periphery. The computation was repeated with a previous model eye for comparison. For the limbal effect, a peak intensity gain of ×22.5 was found at an incident angle of 104° which compares well with previous results. The average intensity gain at this angle was ×7.5 over an area of 0.23 mm 2 . Steeper corneal curvature produced a greater PLF effect. For the crystalline lens effect, maximum UVA (365 nm) intensity gain peaked at ×8.6 at 84° with average intensity gain of ×2.3. The area of UVA exposure peaked at 4.7 mm 2 at 70°. A relatively wide range (30°) of incident angles produced peak PLF gains of ×3 or more in the lens. Significant focusing of light is directed to the nasal limbus, and to a lesser extent to the crystalline lens over a broad range of incident angles. PLF in the nasal cornea is reduced by an order of magnitude when a UV‐blocking soft contact lens is used. The concentration levels and intraocular sites of PLF action on UV and visible light suggest a new mechanism of phakic dysphotopsia and lens phototoxicity.