Retinal photography

A non-mydriatic Canon CR-2 fundus camera (Hospithera, Belgium) with a field of view of 45° was used to obtain high-resolution, optic disc centred images of the fundus of the right eye of each patient at start and end of pulmonary rehabilitation. Patients had to abstain from exercise in the hour prior to the measurement. A trained grader masked to patient characteristics, analyzed the retinal images using semi-automated vessel analysis software developed at VITO (Belgium; http:\\mona.health).

The six largest arterioles and venules coursing through a zone between 0.5 and 1 disc diameter from the optic disc margin were measured and summarized as CRAE and CRVE, representing the average diameter of arterioles and venules of the eye^15,74. Images were not synchronized on the cardiac cycle, but instead retinal vessel diameters of two images were averaged to minimize random variation in retinal vessel diameter due to different stages of the cardiac cycle⁷⁵.

In addition, all images were screened by two ophthalmologist for the following changes: retinal vascular changes (i.e. increased vessel tortuosity, increased venous diameter, retinal hemorrhage, pathological arterio-venous crossings), optic disc changes (i.e. glaucomatous changes/suspect of glaucoma, peripapillary atrophy, peripapillary bleeding, congenital anatomical optic nerve variation, tilted disc, pale optic disc), vitreoretinal or choroidal structural changes (i.e. macular glistening/epiretinal membrane, foveal/perifoveal pigmentary changes, hard exudates, drusen, choroidal nevi). Slightly blurry media was defined as (suspicious of) cataract.