Cataract develops progressively. At an early stage, cataract may only reduce vision a little, but with time a mature cataract can cause marked blindness. Because a cataract forms in the lens of the eye, the eye will not focus properly after cataract surgery without a replacement lens. An intraocular lens is now implanted at the time of surgery for this purpose. Glaucoma A condition where abnormally high pressure of the fluid in the eye causes damage.
Diabetic retinopathy is characterised by the presence of retinal microvascular lesions.
The earliest lesions visible with an ophthalmoscope are termed non-proliferative retinopathy, including microaneurysms, haemorrhages, hard exudates, cotton wool spots, intraretinal microvascular abnormalities and venous beading. The proliferative stage is characterised by growth of new vessels and fibrous tissue and pre-retinal and vitreous haemorrhage. Leak from macular capillaries results in macular oedema, and when present close to the central macula, is termed clinically significant macular oedema. Trachoma Trachoma is a form of conjunctivitis caused by the bacterium, Chlamydia trachomatis . The initial form of the disease, follicular trachoma, is largely a disease of childhood and early adolescence with a peak prevalence in children aged 2 to 3 years.