Multicolor Fundus Imaging better to detect cotton wool spots and photocoagulations scars in diabetic retinopathy

Color fundus photography (CFP) became available for clinical practice in the 1950s and provides fundus images identical to the fundoscopic findings. Over the years, there have been many enhancements to this type of camera, such as wide- and ultra-field views, stereoscopic photography, and non-mydriatic options. The scanning laser ophthalmoscope (SLO), on the other side, was introduced in the 1980s, providing an alternative method for acquiring fundus images.

Ophthalmic imaging modalities have an increasingly important role in the screening, diagnosis, and monitoring of retinal diseases. Currently, the gold standard photography method for the detection of DR is the CFP. Regarding, RVO, The EURETINA guidelines do not specify which image method is more appropriate for documentation and follow-up or retinal lesions.

To evaluate the agreement between conventional fundus photography (CFP) and multicolor fundus imaging (MFI) for the detection of lesions of diabetic retinopathy (DR) and retinal vein occlusion (RVO), Castro et al carried out a study. Cross-sectional analysis of eyes with DR or RVO who underwent CFP and MFI. All images were independently analyzed by two observers (O1 and O2), and the evaluated lesions were classified as “present” or “absent”. Then, a paired comparison between both exams of the same eye was performed, to assess which made it easier to detect the lesions.

Considering DR, the agreement was substantial for cotton wool spots and photocoagulation scars for both observers (O1: κ=0.75 and κ=0.67; O2: κ=0.71 and κ=0.64, respectively) and for hard exudates for O1 (κ=0.80). These lesions were detected more frequently on MFI. Regarding RVO, the agreement was considered substantial for venous sheathing by O1 (κ=0.64) and moderate for optociliary shunts by O2 (κ=0.60). Optociliary shunts were detected more frequently in CPF by both observers and venous sheathing on MFI by O1. For microaneurysms, retinal hemorrhages, retinal neovascularization, and proliferative membranes, in DR, and retinal hemorrhages, venous engorgement, and retinal neovascularization in RVO, the agreement was almost perfect (κ>0.82). In the paired analysis, both observers considered that, in DR, microaneurysms and retinal hemorrhages were easier to detect on CFP and that retinal neovascularization, cotton wool spots, and photocoagulation scars were easier to identify on MFI. Regarding RVO, optocilliary shunts were easier to identify on CFP and venous engorgement on MFI.

Both CFP and MFI can be used in daily clinical practice for diagnosis and follow-up of retinal diseases. The agreement between both exams was substantial to almost perfect for most lesions of both DR and RVO, except for optociliary shunts, in which the agreement was only moderate for O2. Considering lesions with only substantial or moderate agreement by at least one of the observers, cotton wool spots, photocoagulation scars, and hard exudates were detected more frequently on MFI and optociliary shunts on CFP by both observers. Additionally, venous sheathing was detected more frequently on MFI by O1.

In the subjective paired comparison both observers found that, in DR, microaneurysms and retinal hemorrhages were easier to detect on CFP and, on the opposite side, retinal neovascularization, cotton wool spots, and photocoagulation scars were easier to identify on MFI.

Microaneurysms and hemorrhages appear as red lesions on both exams, but on MFI they have a darker red color and the observers found that the contrast against the orange-red fundus was lower compared to CFP, which, in some cases, made them harder to identify and more time consuming.

Cotton wool spots, on turn, appear as white-yellowish pale lesions with poorly defined borders on CFP and as yellow-greenish lesions with well-defined borders on MFI, making the identification on MFI more straightforward.

Photocoagulation scars either appear as pale-white or dark pigmented lesions on CFP and are either bright-white or brown/black on MFI. Pale-white lesions are often very subtle on CFP and can easily go unnoticed, while the bright-white aspect on MFI makes them easier to identify.

Regarding retinal neovascularization, some vascular branches were very subtle on CFP but clearly visible on MFI. In RVO, optociliary shunts were considered easier to identify on CFP. Both observers found that, on MFI, branches within the optic disc were either not visible or had less defined boundaries, while on CFP they were perfectly defined. Venous engorgement, on turn, was more evident on MFI. O1 detected venous sheathing more frequently on MFI and O2 also considered it easier to identify on MFI. Once again, venous sheathing appears as a pale-white contour on the vessel wall on CFP and as a bright green contour on MFI, making the identification straightforward in this last exam. Globally, both observers found that vascular changes (except for microaneurysms and optociliary shunts) were easier to detect with MFI.

In conclusion, the agreement of MFI and CFP to detect lesions in DR and RVO was substantial to almost perfect for most lesions, making them both appropriate exams for screening, diagnosis, or monitoring of retinal changes. Despite this, MFI seems more appropriate to detect cotton wool spots, hard exudates, and photocoagulation scars in eyes with DR earlier changes of the disease (microaneurysms and hemorrhages) seem easier to identify in CFP, authors believe it to be a good screening exam, and that it should keep on being used as the screening tool for the general population, as is recommended in current clinical practice. In turn, MFI may be a better option, in a hospital setting, to evaluate more advanced stages of the disease. Hence, in DR and RVO, in the hospital setting, both CFP and MFI should be performed, to increase diagnostic accuracy and provide more reliable follow-up images. If this is not possible, then the exam of choice should be based on the lesions detected in the fundus observation.

Source: Catarina Castro, João Heitor Marques , Nisa Silva; Clinical Ophthalmology 2023:17 2515–2524