Drusen deposit extracellular yellow material between retinal pigment epithelium (RPE) and Bruch's membrane, consisting of lipids and fatty proteins, mainly oxidized and apolipoproteins. Also, zinc may play a role in blocking complement cascade factor H.
Drusen can be classified by size as hard drusen (small with defined edges), and when they enlarge in size or coalesce, forming soft drusen has blurred edges.
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| Fundus image showing hard drusen |
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| Fundus image showing soft drusen |
Drusen can be different in content as there are homogenous drusen and heterogeneous. The latter indicates transforming (regressing) drusen, a prognostic factor of developing atrophic (Advanced) ARMD.
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| Fundus image showing regressing drusen |
Drusen can come in different shapes, such as reticular pseudodrusen, implying developing advanced or wet ARMD, and drusenoid RPE detachment. It takes years to induce choroidal neovascularization membrane (CNVm) or advanced ARMD.
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| Fundus image showing drusnoid RPE detachment |
Drusen can be different in the location where it can be located in the optic disc forming optic disc drusen, macula, or periphery.
In clinical practice, hard drusen is a sign of early non-neovascular ARMD when combined with intermediate drusen and can be benign without disturbing the ellipsoid zone or causing pigment migration. However, on OCT, hyperreflectivity can be found next to hard drusen as altered Henle fiber layer (HFL). When hard drusen coalesce and enlarge in size can form soft drusen, which becomes more homogenous. Indeed, it can cause disturbed ellipsoid zone and pigment migration, which can be found as hyperreflectivity in OCT's outer retinal tissues.
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| OCT cross-section showing drusen |
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| OCT cross-section showing soft drusen |
Soft drusen are the hallmark of intermediate non-neovascular ARMD, which can come with reduced vision and risk of developing advanced or wet ARMD. Therefore, a close follow-up should be done along with systemic supplements if the other eye suffered from wet/advanced ARMD.
Other types of drusen, such as transforming (Regressing) drusen that features heterogeneous martial on OCT, can be a prognostic factor for atrophy or CNVm formation, the same as for reticular drusen. However, drusenoid RPE detachment needs years to lead to CNVm or an advanced stage of degeneration.
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| OCT cross-section shows regressing drusen |
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| OCT cross-section shows drusnoid RPE detachment |
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