People with diabetes are at high risk of diabetic eye disease such as diabetic retinopathy (DR) which is the most common cause of vision loss. It is caused by damage to the small blood vessels in the retina. If untreated, it may result in varying degrees of vision loss and even blindness. Since DR may cause no symptoms or only mild problems in its early stages, a diabetic person must have regular annual eye exams. During eye exams, doctors often image the retina using fundus cameras for diagnosis. However, fundus cameras are too large and heavy to be transported easily and too costly to be purchased by every health clinic. Therefore, there is a growing demand for small, portable, and inexpensive retinal imaging systems to perform fast DR screening. Recent technological developments have enabled the use of smartphones as biomedical imaging devices. The smartphonebased portable retinal imaging systems available on the market are used only to capture and save retinal images; they do not analyze them using any image processing techniques. In this paper, we investigated the smartphone-based portable ophthalmoscope systems available on the market and compared their field of view to determine if they are suitable for DR screening during a general health screening. Based on the results, iNview retinal imaging system has the largest field of view and better image quality compared with iExaminer, D-Eye, Peek Retina retinal imaging systems.