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K Nusz, N Congdon, B Gramatikov, D Friedman, DL Guyton, C Hylton, DG Hunter; Rapid, Objective Detection of Cataract-induced Blur Using a Bull's Eye Photodetector . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1526.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Cataract impairs the image forming function of the lens. Most strategies to assess the impact of cataract on vision involve subjective assessment of lens opacity or measurement of visual acuity or glare. We have developed a technique to automatically detect when the eye is in focus without specifically measuring refractive error by use of a bull's eye photodetector. The purpose of this study is to determine whether optical aberrations caused by symptomatic cataract can be characterized using this focus detection system. Methods: Instrument Design: To measure a focus signal, each subject was seated adjacent to a lens holder and asked to fixate on an 830 nm laser diode point source at 40 cm for 0.3 s. Reflected light was focused back toward the point source by the optical system of the eye. A beam splitter deflected returning light toward a bull's eye photodetector (consisting of an annulus (A) and center (C) of equal area). The focus detection value C-A was measured. With this arrangement, when the eye is out of focus, returning light is imaged equally onto C and A, and C-A 0. When the eye is in focus, most returning light is imaged onto C, and C-A ≷ 0. Participants: 20 subjects, 15 women and 5 men ranging in age from 50 to 81, scheduled to undergo surgery for symptomatic cataract. Study design: Pre-operative lens photographs were obtained and graded by an ophthalmologist masked to patient identity. Visual acuity, refractive error, and pupil size were measured. To measure focus curves for an eye, C-A was recorded using a series of lenses selected to span the point of best focus. Astigmatism ≷ 1D was corrected with an additional lens. Ten measurements were obtained with each lens, with outlier measurements ≷1.5 SD automatically discarded. The measurements were repeated approximately 6 weeks after standard cataract extraction and intraocular lens insertion. Main Outcome Measures: Total signal strength, peak height, and peak width. Results: 2 subjects were excluded (retinal detachment, cognitive deficits). In the remaining 18 subjects, average visual acuity improved from 20/56 to 20/35 (p=0.01). Average focus detection signal strength increased from 0.003 to 0.012 (p=0.006). Average peak height increased from 0.006 to 0.026 (p=0.006). Peak width decreased from 3.639 D to 1.798 D (p=0.003). Conclusion: The focus curves generated by the focus detection system corresponded with the improved optical performance of the eye after cataract extraction. This approach may someday allow for rapid, objective detection of optical aberrations induced by cataract.
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