Light-intensity distribution in eccentric photorefraction crescents

Kusel, R.; Oechsner, Ulrich; Wesemann, W.; Russlies, Stephan; Irmer, Eva M.; Rassow, B.

doi:10.1364/josaa.15.001500

Cited by 5 publications

(2 citation statements)

References 18 publications

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“…This means the measurement range can be enlarged and 'dead zone' is disappearing. (4). The length of the line source should be reasonable.…”

Section: Relative Light Intensitymentioning

confidence: 99%

“…Many technique improvements and theory analysis have being reported to increase the accuracy of the method. 2,3,4 To date, however, there is no entirely satisfactory optical theory that quantitatively explains the intensity distribution on whole pupil image with any defined light source and camera aperture. According to the working principle, the method assessing the refractive errors is greatly relying on the crescent pattern of the pupil image or on the intensity gradient in the principal meridian across the pupil.…”

Section: Introductionmentioning

confidence: 99%

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Intensity distribution topography on pupil"s image in EPR

et al. 2005

SPIE Proceedings

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Eccentric photorefraction (EPR), which is used to determine the refractive error of eye, is greatly relied on the crescent pattern of the pupil image or on the intensity gradient in the principal meridian across the pupil. The vignetting image of the pupil, which is formed by a camera lens aperture with an eccentric light source, and contains a lot of refractive information of the subject eye, has been studied by many authors expecting to get more accurate measurement. In this paper, we have investigated the formation of the crescent image of the pupil. A mathematical expression that calculates the relative intensity in the whole pupil is derived. The intensity distribution is shown in a topography figure that gives a more clear understanding of the pupil image. Based on the discussion of the point light source, light sources are then further extended to other shapes such as line, circle or rectangular form for more general cases, simply by integrating the point source over the scale of the actual geometric form. The analysis and calculation presented are based on Gaussian optics for simplicity. The investigation results show that line source with 0 eccentricity at its one end is suggested in the EPR, in which the intensity slope is much sensitive to the refractive states.

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“…This means the measurement range can be enlarged and 'dead zone' is disappearing. (4). The length of the line source should be reasonable.…”

Section: Relative Light Intensitymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Intensity distribution topography on pupil"s image in EPR

et al. 2005

SPIE Proceedings

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show abstract

Objective Refraction: Retinoscopy, Autorefraction, and Photorefraction

Campbell¹,

Benjamin²,

Howland³

2006

Borish's Clinical Refraction

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Computer-based Real-Time Analysis in Mobile Ocular Screening

Chen

Lewis

Kerr

et al. 2006

Telemedicine and e-Health

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Mobile ocular telemedicine is potentially an effective method to provide service in medically underserved areas and to screen large populations for abnormalities. Currently, digital images are acquired, stored, and transferred to readers for evaluation, after which the results are provided to the subjects. The transfer of large image files and the timeliness of the subsequent reading of images are significant factors for practical implementation of effective telemedicine screening. This work examines the feasibility of in situ real-time computer analysis of digital images to determine and classify the image results as normal and abnormal. This retrospective study used a photoscreening database of 360 patients ranging in ages from 6 months to 18 years. Computer analysis automatically classified the binocular photorefraction (PR) images, and these PR results were compared to those of the subjective clinical eye examinations provided. With an average processing time of approximately 15 seconds per examinee, the analysis found that the PR results can be categorized as: a positive group that requires referral (186 cases) with a predictive value of 98.9% (2 false-positives); a negative group (144 cases) with a predictive value of 89.6% (15 false-negatives); and an uncertain group (30 cases or 8.3%) that required resolution by readers. The real-time analysis code reduces by approximately 92% the manpower for image grading and electronic transmission at this stage of ocular evaluation. These results indicate the feasibility of this approach.

show abstract

Light-intensity distribution in eccentric photorefraction crescents

Cited by 5 publications

References 18 publications

Intensity distribution topography on pupil"s image in EPR

Intensity distribution topography on pupil"s image in EPR

Objective Refraction: Retinoscopy, Autorefraction, and Photorefraction

Computer-based Real-Time Analysis in Mobile Ocular Screening

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