Table 2.

Research Questions.

RQ No	Questions	Motivation
RQ1	What clinical features of retinal image are required for DR detection and classification, and which deep learning methods are mostly used to classify DR problems?	To answer this question, an overview of the current trends in deep learning in DR classification has been reviewed. The answer to this research question will help researchers in selecting the best deep learning technique to use as a baseline in their research.
RQ2	Which DR dataset have been acquired, managed, and classified to identify several stages of DR?	Identify available dataset to help researchers to use dataset as a benchmark and can compare the performance with their work.
RQ3	What are the open issues and challenges of using deep learning methods to detect DR?	This question will allow researchers to recognize open research challenges and future directions in order to detect DR by using more advanced deep learning techniques.