Screening looks for changes that are suspicious for the early stages of sight-threatening retinopathy. A follow-up appointment is not a diagnosis, it's an indication that further tests are needed. Many people who are referred to ophthalmology for further investigation end up needing no treatment and are returned to screening. If the tests show that treatment is needed, regular screening should have picked up the changes at a stage when treatment is most effective - this is usually before there is any effect on vision.
Sometimes people worry that needing new glasses may be an indication that they have vision loss due to diabetic retinopathy but when diabetic retinopathy does affect eyesight it is not correctable by glasses. If your eyesight is poor during the screening test when wearing glasses, you may be asked to read the eye chart using a pinhole - this should eliminate any problems due to out of date glasses and tests how well the retina is working.
The way to minimize the risk of progression of diabetic retinopathy is to maintain good control of blood glucose, blood pressure and blood lipids and to attend all screening appointments. Eye-lid twitching is not at all related to diabetic retinopathy.