The macula is the part of the retina where light falls when we look directly at an object - it's therefore very important for reading, watching TV, looking at people's faces etc.. Sometimes diabetic retinopathy can affect the blood vessels in the macula, making them leaky. This can lead to swelling within the macula which, if severe enough, damages the photoreceptors, making vision blurred. Screening aims to detect maculopathy at a very early stage, before vision is affected, when treatment is most effective.
Following a referral for maculopathy, someone will usually be given an OCT scan. Depending on the results, the person may be returned to screening (if the maculopathy has cleared up by itself), returned to digital surveillance by the screening programme (if the maculopathy is very mild), monitored within the hospital eye service (if the maculopathy is borderline) or offered treatment (if the maculopathy is considered to be significant).
This page gives more detailed information about the condition and treatment, including lifestyle changes which can help reduce the risk of progression:-
http://www.diabeticretinopathy.org.uk/diabetic_maculopathy.html