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Pors LJ, Haasjes C, van Vught L, Hoes NP, Luyten GPM, van Rijn GA, Vu THK, Rasch CRN, Horeweg N, Beenakker JWM. Correction Method for Optical Scaling of Fundoscopy Images: Development, Validation, and First Implementation. Invest Ophthalmol Vis Sci 2024; 65:43. [PMID: 38271188 PMCID: PMC10829800 DOI: 10.1167/iovs.65.1.43] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Accepted: 12/28/2023] [Indexed: 01/27/2024] Open
Abstract
Purpose Although fundus photography is extensively used in ophthalmology, refraction prevents accurate distance measurement on fundus images, as the resulting scaling differs between subjects due to varying ocular anatomy. We propose a PARaxial Optical fundus Scaling (PAROS) method to correct for this variation using commonly available clinical data. Methods The complete optics of the eye and fundus camera were modeled using ray transfer matrix formalism to obtain fundus image magnification. The subject's ocular geometry was personalized using biometry, spherical equivalent of refraction (RSE), keratometry, and/or corneal topography data. The PAROS method was validated using 41 different eye phantoms and subsequently evaluated in 44 healthy phakic subjects (of whom 11 had phakic intraocular lenses [pIOLs]), 29 pseudophakic subjects, and 21 patients with uveal melanoma. Results Validation of the PAROS method showed small differences between model and actual image magnification (maximum 3.3%). Relative to the average eye, large differences in fundus magnification were observed, ranging from 0.79 to 1.48. Magnification was strongly inversely related to RSE (R2 = 0.67). In phakic subjects, magnification was directly proportional to axial length (R2 = 0.34). The inverse relation was seen in pIOL (R2 = 0.79) and pseudophakic (R2 = 0.12) subjects. RSE was a strong contributor to magnification differences (1%-83%). As this effect is not considered in the commonly used Bennett-Littmann method, statistically significant differences up to 40% (mean absolute 9%) were observed compared to the PAROS method (P < 0.001). Conclusions The significant differences in fundus image scaling observed among subjects can be accurately accounted for with the PAROS method, enabling more accurate quantitative assessment of fundus photography.
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Affiliation(s)
- Lennart J. Pors
- Department of Radiation Oncology, Leiden University Medical Center, Leiden, the Netherlands
- Department of Ophthalmology, Leiden University Medical Center, Leiden, the Netherlands
| | - Corné Haasjes
- Department of Radiation Oncology, Leiden University Medical Center, Leiden, the Netherlands
- Department of Ophthalmology, Leiden University Medical Center, Leiden, the Netherlands
- Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands
| | - Luc van Vught
- Department of Ophthalmology, Leiden University Medical Center, Leiden, the Netherlands
- Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands
| | - Noor P. Hoes
- Department of Ophthalmology, Leiden University Medical Center, Leiden, the Netherlands
| | | | - Gwyneth A. van Rijn
- Department of Ophthalmology, Amsterdam University Medical Center, Amsterdam, the Netherlands
- Department of Ophthalmology, Northwest Clinics, Alkmaar, the Netherlands
| | - T. H. Khanh Vu
- Department of Ophthalmology, Leiden University Medical Center, Leiden, the Netherlands
| | - Coen R. N. Rasch
- Department of Radiation Oncology, Leiden University Medical Center, Leiden, the Netherlands
| | - Nanda Horeweg
- Department of Radiation Oncology, Leiden University Medical Center, Leiden, the Netherlands
- Department of Ophthalmology, Leiden University Medical Center, Leiden, the Netherlands
| | - Jan-Willem M. Beenakker
- Department of Radiation Oncology, Leiden University Medical Center, Leiden, the Netherlands
- Department of Ophthalmology, Leiden University Medical Center, Leiden, the Netherlands
- Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands
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