増殖型糖尿病性網膜症の網膜硝子体界面病変とbursa premacularis

Implication of bursa premacularis in proliferative diabetic retinopathy

　我々は，先にその存在を証明したbursa　premacularisが，増殖型糖尿病性網膜症（PDR）の病型形成にどのように関与しているか検索した。対象は，網膜前出血から牽引性網膜剥離を含むPDR 384眼である。PDRは，硝子体の緩慢な収縮に伴って進行する。有形硝子体が収縮すると，硝子体は眼底から剥離する。しかし，後極部では眼底の前方にポケット状の液化腔（bursa）が存在するため，硝子体ゲルの牽引が後部硝子体膜に伝わらず，後部硝子体膜の剥離が起きない。こうして，すりばち状の不完全硝子体剥離が形成される。新生血管増殖膜は，硝子体膜の立上がりに沿って成長し，輪状の網膜硝子体癒着が形成される。従って，PDRの増殖病変はbursaの形態を模倣すると言える。硝子体の収縮が更に進行すると，後部硝子体膜を介した牽引が黄斑部に及び，牽引雛や浮腫を生ずる。網膜前出血の解釈には，bursa内出血という可能性の追加が必要である。

We defined, in an earlier anatomical study, the bursa premacularis as a pocket-like lacuna of the vitreous located just anterior to the posterior fun-dus. We evaluated the state of the vitreous in 384 eyes with proliferative diabetic retinopathy (PDR). The series widely ranged in severity, including eyes with preretinal hemorrhage alone to tractional retinal detachment.

We could confirm that the presence of the bursa played crucial roles in clinical manifestations of PDR. During the stage of gradual contraction of the vitreous, an incomplete posterior vitreous detach-ment (PVD) is formed. The fundus area facing the bursa is spared from the tractional force of PVD, asthe posterior hyaloid membrane (PHM) is separat-ed from the vitreous gel proper by the presence of the bursa. The tractional force by the PVD is excerted to the area surroundng the bursa instead.

After this incomplete PVD is established, fi-brovascular formation is the usual event along the outer border of the bursa, forming firm vitreo-retinal adhesion. Further tractional force would be transmitted to the macular area through the PHM and would result in tractional retinal fold and macular edema.

We also identified cases in which apparent pre-retinal hemorrhages actually proved to be hemor-rhages in the bursa itself.