Undilated versus dilated monoscopic smartphone-based fundus photography for optic nerve head evaluation
Smartphone-based fundus photography (SBFP) allows for a cheap and mobile fundus examination with the potential to revolutionize eye care especially in low income settings. The purpose of this study was to assess the impact of pupil dilation on image quality in optic nerve head (ONH) imaging and vertical cup-to-disc ratio (vCDR) evaluation with SBFP. Eyes with glaucoma or suspected to have glaucoma were imaged with conventional digital fundus photography (CFP) and SBFP undilated and following dilation, all monoscopically. SBFP was possible in 74% of eyes without dilation and in 98% following dilation. Better image quality on SBFP was achieved with dilation and complete visualization of the optic disc rim was possible in 46% of images without dilation and on 94% of images with dilation. VCDR measurements on images obtained following dilation highly correlated with measurements on CFP (coefficient of correlation r = 0.91, p < 0.001), whereas vCDR on images obtained without dilation correlated less well with CFP (r = 0.70, p < 0.001). SBFP for ONH evaluation is promising, however dilation appears mandatory to achieve results comparable to optic disc evaluation on CFP. ONH imaging with smartphones without dilation might bear the risk of underestimating the CDR and hence overlooking patients at risk for glaucoma.
Smartphone-based fundus photography (SBFP) allows for a cheap and mobile fundus examination and documentation with the potential to revolutionize eye care especially in low income countries1,2,3,4. With the advent of SBFP multiple applications in ophthalmology have been accomplished including smartphone-based diabetic retinopathy screening5,6,7,8,9,10. Although optic nerve head (ONH) evaluation would be another natural application of SBFP, there is a dearth of literature on the application of SBFP for glaucoma screening to date11,12. As the vertical cup-to-disc ratio (vCDR) has proved to be a simple, relatively robust index of glaucomatous loss of the neuroretinal rim13,14, ONH evaluation using SBFP may be applicable in glaucoma screening. If the camera’s light beam and the illumination source are adequately coaxial, SBFP can even be performed without pupil dilation, which further simplifies its application15,16.
In the study by Russo et al. undilated SBFP with a D-Eye adapter and an iPhone 5 s was compared to undilated clinical 90D lens biomicroscopy for vCDR evaluation11. Agreement between the two modalities was good (kappa = 0.63) and SBFP was possible in 97% of the eyes (104 out of 107). However only undilated SBFP has been performed. Bastawrous and coworkers compared dilated SBFP with a Peek Retina adapter and a Samsung S3 to dilated conventional digital fundus photography for vCDR evaluation12. Also this study revealed good agreement (kappa = 0.69) and SBFP was possible in 80% of the eyes (2322 out of 2920).
With glaucoma being a major cause for irreversible blindness more studies on the applicability of SBFP for glaucoma screening and the evaluation of glaucomatous optic discs are warranted. The comparison of dilated to undilated SBFP with the latter being more feasible in a low income setting is of particular interest. So far, image quality and agreement in vCDR evaluation have not been compared between undilated and dilated SBFP. Thus we performed this study.
MethodsSubject recruitment
Patients were consecutively recruited from the glaucoma outpatient clinic at the Department of Ophthalmology of the University of Bonn, Germany. Ethical approval was obtained from the ethics committee of the University of Bonn and informed consent was obtained from all study participants prior to study inclusion. The Declaration of Helsinki was followed. Exclusion criteria were any retinal diseases and severe media opacities.
Image acquisition
Eyes were imaged with a Galaxy S4 (Samsung Electronics, Seoul, South Korea) using the D-Eye adapter (Fig. 1, version from 2016, D-EYE S.r.l., Padova, Italy) monoscopically first undilated and then dilated. The D-Eye adapter’s optics consist of a negative lens, a beam splitter, a mirror and polarized filters and allow for smartphone-based direct ophthalmoscopy15. Additionally eyes were imaged with conventional monoscopic fundus photography (CFP) (Visucam 500, Carl Zeiss Meditec, Jena, Germany), also dilated. The Galaxy S4 backside camera is equipped with a 12.8 megapixel CMOS (“complementary metal-oxide-semiconductor”) sensor and the Visucam 500 with a 5.0 megapixel CCD (“charge-coupled device”) sensor. The working distance for image acquisition was 10–30 mm for the Galaxy S4 with the D-Eye adapter and 40 mm for the Visucam 500. SBFP was performed by the same examiner, experienced in direct and indirect SBFP, in all patients (MWMW) in a darkened room. After 5 minutes of unsuccessful imaging attempts examination was aborted.
Image analysis
For analysis only the central circular part of the image was cropped using Image J17 in order to mask for the status of dilation. All images were pseudonymized and analyzed by two masked graders (MWMW and CKB). Image quality was graded using a six-step-scale with exemplary images based on vessel visibility (Fig. 2). Optic disc rim visualization and degree of optic disc pallor were evaluated using a respective three-step-scale with exemplary images (Figs 3 and 4). VCDR was evaluated by measuring the total ONH height and the height of the superior and inferior neuroretinal rim with Image J, entering the results in an Excel table and vCDR was automatically calculated. Statistical analyses were performed with R (R: A Language and Environment for Statistical Computing, R Core Team, R Foundation for Statistical Computing, Vienna, Austria, 2016). Photographic vCDR assessment on CFP was compared with assessment from the medical records based on stereoscopic slit lamp biomicroscopy. Weighted kappa (for image quality, optic disc pallor and degree of optic disc rim visualization) and intraclass correlation (for vCDR) were calculated to assess inter-observer reliability.
Data availability
The datasets generated during and analyzed during the current study are available from the corresponding author on reasonable request.
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