Dr Loon is the Head of Ophthalmology at Alexandra Hospital. He specialises in performing laser and surgery for glaucoma, as well as complex cataract surgery. He also specialises in the epidemiology of eye diseases, using the research of eye disease in applying the latest technologies whilst ensuring safety and efficacy in treatment.

He received his basic training in Singapore, with specialist degrees conferred from the National University of Singapore and Edinburgh. He underwent further fellowship and training in Sydney University, where he obtained a second Masters of Medicine (Merit) in Clinical Epidemiology.

He is also keen in medical outreach, and has done medical mission work in Bangladesh, China, Indonesia and Nepal with like-minded friends and colleagues. In 2011, he was conferred the Humanity Award by President Nathan for his work in medical mission work.