Keep BP <150/85 and all the major diabetic retinopathies are less common.1Diabetes can be bloody and blinding the leading cause of blindness in those aged 20-65 (UK). Almost any part of the eye can be affected: cataract and retinopathy are the chief pathologies.
30% of adults have ocular problems when diabetes presents. At presentation, the lens may have a higher refractive index (possibly due to dehydration) producing relative myopia. On treatment, the refractive index reduces, and vision is more hypermetropic so do not correct refractive errors until diabetes is controlled.
30% of adults have ocular problems when diabetes presents. At presentation, the lens may have a higher refractive index (possibly due to dehydration) producing relative myopia. On treatment, the refractive index reduces, and vision is more hypermetropic so do not correct refractive errors until diabetes is controlled.
Structural changes
Diabetes accelerates formation and progress of age-related cataract. Typically this is premature senile cataract, but young diabetics can also be affected at presentation; here the lens has taken up a lot of glucose which is converted by the aldolase reductase to sorbitol. Rarely, diabetes affects the iris, with new blood vessel forming on it (rubeosis), and, if these block the drainage of aqueous fluid, glaucoma may result.
Retinopathy
Pathogenesis
Microangiopathy in capillaries, precapillary arterioles and venules causes occlusion leakage.
Vascular occlusion
causes ischaemia which leads to new vessels in the retina, optic disc, and iris, ie proliferative retinopathy. New vessels can bleed (vitreous haemorrhage). As new vessels carry along with them fibrous tissue, retraction of this tissue increases risk of retinal detachment. Occlusion also causes cotton wool spots, (ischaemic nerve fibres).
Vascular leakage
As pericytes are lost, capillaries bulge (microaneurysms) and there is oedema & hard exudates (made up of lipoprotein & lipid filled macrophages). Rupture of microaneurysms, at the nerve fibre level causes flame shaped haemorrhages; when deep in the retina, blot haemorrhages form.
Pre-symptomatic screening enables laser photocoagulation. Screen by regular eye exam or retinal photography. In rural areas, mobile screening has a role. [n=2186] Lesions are mostly at the posterior pole and can be easily seen by ophthalmoscope. Background retinopathy comprises microaneurysms (seen as dots), haemorrhages (flame shaped or blots) and hard exudates (yellow patches). Vision is normal. Background retinopathy can progress to sight-threatening maculopathy proliferative retinopathy.
Maculopathy
Leakage from the vessels close to the macula cause oedema & maculopathy.
Proliferative retinopathy
Fine new vessels appear on the retina. Engorged tortuous veins, cotton wool spots, large blot haemorrhages & vitreous haemorrhage.
Refer those with maculopathy or proliferative retinopathy urgently to an ophthalmologist for treatment (eg photocoagulation) to protect vision.
Treatment
Good control of diabetes can prevent new vessel formation. Concurrent diseases may accelerate retinopathy (eg hypertension, renal disease, pregnancy, and anaemia). Treat these (as appropriate), and hyperlipidaemia. Photocoagulation by laser is used to treat both maculopathy and proliferative retinopathy. Definite indications for photocoagulation are new vessels on the optic disc and vitreous haemorrhage. If vitreous haemorrhage is massive and does not clear, vitrectomy may be needed.
CNS effects
Ocular palsies may occur, typically nerves III and VI. In diabetic third nerve palsy the pupil may be spared as fibres to the pupil run peripherally in the nerve, receiving blood supply from the pial vessels. Argyll Robertson pupils and Horner's syndrome may also occur .
Proliferative diabetic retinopathy may be treated with panretinal (scatter) laser photocoagulation (PRP). This type involves treating the peripheral retina which is not receiving adequate blood flow. By treating these areas it is thought that the stimulus driving the neovascular process may be halted. As this treatment involves many laser applications (eg >1000) it may be divided into 2 sessions. NB: panretinal photocoagulation does not improve vision. It is intended to help prevent blindness. It may cause some loss of peripheral, colour, and night vision. Some patients get generalized blurring of vision which is usually transient but may persist indefinitely.
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| Retinopathy after the laser |
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| Retinopathy before the laser |
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