Đây là những đầu tiên tổn thương lâm sàng phát hiện bệnh võng mạc tiểu đường (hình 16,1). Họ xuất hiện nhỏ, tròn, dấu chấm màu đỏ và có thể được tìm thấy trong bất kỳ một phần của võng mạc, mặc dù họ chiếm ưu thế ở cực sau của mắt. Họ không phải là liên kết với bất kỳ mạch máu | 140 SECTION III DIABETIC RETINOPATHY AND ASSOCIATED OPHTHALMIC DISORDERS Microaneurysms These are the very earliest clinically detectable lesions of diabetic retinopathy Fig. . They appear as small round red dots and may be found in any part of the retina although they predominate in the posterior pole of the eye. They are not associated with any visible blood vessels and represent localized dilatations of retinal capillaries. The number of microaneurysms increases with increasing severity of retinopathy. A microaneurysm indicates a localized area in the microvascular circulation where the blood-retinal barrier is deficient and may therefore be associated with abnormal vascular leakage. The pathogenesis of microaneurysms is unclear but they may represent outpouchings of capillaries at areas of relative weakness where there is pericyte loss. Pericytes are cells which partly enclose retinal capillaries and may be considered the smooth muscle equivalent of the microvasculature pericyte numbers diminish early in the development of diabetic retinopathy. Microaneurysms may also represent a localized response to surrounding hypoxia a limited proliferative process as they tend to predominate in areas where there is closure of surrounding capillary beds. Haemorrhages Haemorrhages co-exist with microaneurysms but are more variable in their appearance Fig. . At their smallest they may be difficult to differentiate from microaneurysms. A haemorrhage unlike a microaneurysm is not nec- Fig. Moderate background diabetic retinopathy with microaneurysms haemorrhages and exudates. CHAPTER 16 CLASSIFICATION AND DIAGNOSIS 141 essarily round and may take on a variety of outlines the phrase dot and blot is an apt description. Haemorrhages can occur within the retina where they remain confined by the retina or they can occur on the retinal surface flameshaped haemorrhage where they spread out over the superficial nerve fibre layer taking on a characteristic flame .
