As a truck driver who drove eight hours a day transporting goods between Hong Kong and the mainland, Larry Ho, 46, was used to long hours on the road. One day while driving, however, Ho (whose name has been changed for patient confidentiality reasons) noticed something strange floating to the right side of his visual field. The image started to blur and within an hour he could no longer see with his right eye. Terrified, he pulled over, flagged down a taxi and headed straight for a mainland clinic. As his family's sole breadwinner, his sight was more than his window on the world - it was his means of providing for his wife and four-year-old son. While his right eye looked normal on the outside, peering in, the doctor saw that he was bleeding inside his eyeball, behind the lens. The bleeding was so severe that the vitreous humour (the normally clear, gel-like substance that fills the cavity of the eyeball) was badly clouded with blood. The doctor examined Ho's left eye, and saw abnormalities that might be caused by diabetic changes. However, the patient was in no immediate danger of losing the sight in his left eye. Ho, a Hong Kong resident, decided to seek treatment back home. He consulted Dr Chan Wai-man, a specialist in ophthalmology at the Hong Kong Sanatorium and Hospital. Chan's investigations confirmed that the vitreous humour in Ho's right eye was completely occluded by blood. He found that the surface of Ho's left retina was covered with tiny dots of clotted blood. These tiny blood clots - or dot-blot haemorrhage - indicated that abnormal, brittle blood vessels had started to grow. The left eye also showed signs of macular edema, or retina swelling. Chan strongly suspected that there was a proliferation of abnormal blood vessels in Ho's right eye, and that one or more of those blood vessels had ruptured. The profuse growth of abnormal blood vessels in the eye is often caused by diabetes. Because abnormally high blood sugar levels can affect microcirculation, organs with a profusion of tiny blood vessels such as the eyes and kidneys are more susceptible to damage. As the tiny blood vessels become damaged from sluggish blood circulation, the organ suffers from ischaemia - a deprivation of blood and oxygen. To compensate, the body releases growth factors to spur the growth of new blood vessels to carry more oxygen to the organ. However, these new blood vessels are fragile and can cause complications, including the vitreal haemorrhage that Ho experienced. A blood test confirmed that Ho, indeed, did have diabetes. Healthy fasting blood sugar levels should be less than 6.1 mmol/L (millimoles per litre) and anything higher than 7 mmol/L is indicative of diabetes. Ho's readings were 10.2 mmol/L. The findings surprised Ho, who had always considered himself to be in good health despite being obese and lacking exercise. In hindsight, he realised that he had been more thirsty than normal in the past few months, and had needed to urinate more frequently. But he missed these early signs of diabetes because he shrugged off the symptoms and was too busy to have a health check. Chan starting treating Ho with a vitrectomy of the right eye. He made a tiny hole in the eyeball and painstakingly removed the blood clot one piece at a time. Once the occluded vitreous humour was removed, Chan saw that Ho's retina was covered in abnormal blood vessels, which he then trimmed and cauterised with a laser, effectively sealing them off and preventing future haemorrhaging. However, the procedure, called photocoagulation by laser, also leads to some vision loss, as it damages the retinal receptors. Chan says Ho's circulation was so poor that it could not support all the receptors on the retina. Hence, peripheral vision receptors had to be sacrificed so that central vision could be maintained. The two-hour-long procedure enabled Ho to retain 20/20 central vision in his right eye but he lost 50 per cent of his peripheral vision. After Ho's right eye stabilised, Chan began treating the left eye. Because its diabetic changes, namely macular edema, were at an earlier stage, and thanks to medical advancements, a more benign treatment could be used. Until five or six years ago, the only was to treat this stage of the condition was laser photocoagulation. However, a new outpatient treatment now enables antibodies to be injected into the eye to neutralise the growth factors that stimulate abnormal blood vessel growth (so Ho's left eye vision was able to be preserved). Less than a month after the injection, Ho's retinal thickness returned to normal. Separately, he also sought treatment for his diabetes and learned how to eat and live more healthily. In less than two months, Ho was back on the road. According to Chan, diabetes is the leading cause of blindness for middle-aged people. Many cases of macular edema and retinal angiopathy (disease of the blood vessels in the eye) go unnoticed in the early stages. Untreated, the scarring left by the ruptured blood vessels can pull on the retina, which lines the inside of the eye cavity, resulting in retinal detachment. If things progress to this stage, blindness will be permanent. Although the events leading to the discovery of Ho's conditions were dramatic and terrifying, the experience was a blessing in disguise as it alerted him to his health condition early enough for a successful intervention.