We first try to understand the problem we will be dealing with. The below image (credit: https://www.eyeops.com/) tells us the 5 very common symptoms of DR(diabetic retinopathy).

The Kaggle competition that introduced the dataset wrote:

You are provided with a large set of retina images taken using fundus photography under a variety of imaging conditions. A clinician has rated each image for the severity of diabetic retinopathy on a scale of 0 to 4:

0 - No DR

1 - Mild

2 - Moderate

3 - Severe

4 - Proliferative DR

Like any real-world data set, you will encounter noise in both the images and labels. Images may contain artifacts, be out of focus, underexposed, or overexposed. The images were gathered from multiple clinics using a variety of cameras over an extended period of time, which will introduce further variation.