EXTENDED REPORT

A method of drusen measurement based on reconstruction of fundus background reflectance

R T Smith, J K Chan, T Nagasaki, J R Sparrow and I Barbazetto

Department of Ophthalmology, Columbia University, New York, NY, USA

Correspondence to:
Correspondence to:
Dr R T Smith
Harkness Eye Institute Columbia University College of Pysicians and Surgeons, New York, NY10032, USA; rts1{at}columbia.edu

Background: The hallmarks of age related macular degeneration (AMD) are the subretinal deposits known as drusen. Current manual methods of drusen segmentation and quantification are laborious and subjective. The authors introduced a digital method and tested it for accuracy and reliability.

Methods: Fourteen eyes with drusen were selected. The authors digitally reconstructed the macular background using normal background areas ("dots") fitted to quadratic polynomials in two zones. The model was used to level the reflectance for the purpose of segmenting drusen by a global threshold. Measurements of drusen areas were compared with those of a semi-automated background levelling technique and manual drawings from stereo pairs.

Results: Intraobserver reproducibility had standard deviations from 0.1% to 4.1%. Interobserver reproducibility yielded 95% limits of agreement of –2.7% to 6.3%. The dots method compared with manual drawings and with the semi-automated method had 95% limits of agreement of –8.3% to 2.8% and –7.1% to 4.8%, respectively.

Conclusions: The dots method was reproducible and accurate with respect to validated methods. It provided less total operating time and greater precision than that of standard fundus photo grading. With implementation of commercial software, this technique for macular image analysis has potential for use in clinical research.

Abbreviations: AMD, age related macular degeneration; CMGS, Columbia Macular Genetics Study

Keywords: age related macular degeneration; digital imaging; drusen; macula; quantification

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• Smith, R. T., Chan, J. K., Busuoic, M., Sivagnanavel, V., Bird, A. C., Chong, N. V. (2006). Autofluorescence Characteristics of Early, Atrophic, and High-Risk Fellow Eyes in Age-Related Macular Degeneration. IOVS 47: 5495-5504 [Abstract] [Full Text]  
• Smith, R. T., Chan, J. K., Nagasaki, T., Ahmad, U. F., Barbazetto, I., Sparrow, J., Figueroa, M., Merriam, J. (2005). Automated Detection of Macular Drusen Using Geometric Background Leveling and Threshold Selection. Arch Ophthalmol 123: 200-206 [Abstract] [Full Text]